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Integrating systems of desalination and potable reuse: reduced energy consumption for increased water supply

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Integrating systems of desalination and potable reuse: reduced energy consumption for increased water supply

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Content Copyright 2021 Xin Wei
Integrating Systems of Desalination and Potable Reuse:
Reduced Energy Consumption for Increased Water Supply
by
Xin Wei
A Dissertation Presented to the
Faculty of the USC Graduate School
University of Southern California
In Partial Fulfillment of the
Requirements for the Degree of
Doctor of Philosophy
Engineering
(Environmental Engineering)
August 2021

ii
Acknowledgements
First of all, I would express my deep appreciation to my main advisor, Professor Amy Childress,
for the best mentorship and solid support. I learnt a lot from her high standards on research work, her
expertise and knowledge, and spirit of exploration. It’s my great honor and pleasure to be a part of her
research group for the past four years.
I would also thank my second great advisor, Professor Kelly Sanders. I deeply appreciate her
mentorship and help in the past four years. Her profound knowledge and resourcefulness lead our
research project to its current direction.
I would also like to thank my committee members: Professor Daniel McCurry, Professor Adam
Smith, and Professor Mitul Luhar, for their feedbacks and comments, which significantly improve the
quality of my work. I also want to extent my thanks to my previous and current colleagues, who provides
supports in my study and life: Dr. Christopher Morrow, Dr. Ryan Gustafson, Dr. Allyson McGaughey,
Sophia Plata, Weijian Ding, Sultan Alnajdi, Shounak Joshi, and Bana Dahdah.
Lastly, I would like to thank my parents and family, who always support and love me. Even
though you are thousands of miles away from me, I can still feel your love. I would thank my husband for
his love and understanding during this special journey of my life. Thank you for taking care of me for
every single day.
Support
This work was supported by the Electric Power Research Institute (10007871), the University of
Southern California’s Theodore and Wen-Hui Chen Endowed Fellowship, and the University of Southern
California’s Viterbi/Graduate School Ph.D. Fellowship.

iii
Table of Contents
Acknowledgements ....................................................................................................................................... ii
List of Figures ............................................................................................................................................... vi
List of Tables ................................................................................................................................................ ix
Abstract ......................................................................................................................................................... x
CHAPTER 1. ................................................................................................................................................. 1
1.1 Introduction .................................................................................................................................... 1
1.2 Background ................................................................................................................................... 2
1.2.1 Wastewater potable reuse .................................................................................................... 2
1.2.2 Seawater desalination ........................................................................................................... 3
1.2.3 Similarities between potable reuse and SWRO treatment trains .......................................... 4
1.3 Objectives ...................................................................................................................................... 4
1.4 Dissertation organization ............................................................................................................... 6
2 CHAPTER 2. A Modeling Framework to Evaluate Blending of Seawater and Treated Wastewater
Streams for Synergistic Desalination and Potable Reuse ............................................................................ 7
Abstract...................................................................................................................................................... 7
2.1 Introduction and background ......................................................................................................... 8
2.1.1 Seawater reverse osmosis desalination ............................................................................... 8
2.1.2 Synergistic opportunities in coastal water system ................................................................ 9
2.2 Material and methods .................................................................................................................. 11
2.2.1 System model framework .................................................................................................... 11
2.2.2 Overview of scenarios ......................................................................................................... 11
2.2.3 Process models ................................................................................................................... 14
2.2.3.1 Pre-treatment .............................................................................................................. 15
2.2.3.2 Reverse osmosis ......................................................................................................... 15
2.2.3.3 Second-pass RO for boron removal ............................................................................ 16
2.2.3.4 Post-treatment ............................................................................................................. 16
2.2.4 Estimation of energy consumption ...................................................................................... 17
2.3 Results and discussion ............................................................................................................... 18
2.3.1 RO brine salinity .................................................................................................................. 18
2.3.2 Treated wastewater flowrates in hybrid systems ................................................................ 19
2.3.3 Discharge flowrates in hybrid systems ................................................................................ 21
2.3.4 Boron concentration in RO permeate.................................................................................. 22
2.3.5 Specific energy consumption and specific energy savings in hybrid systems .................... 22
2.3.5.1 Specific energy consumption of RO ............................................................................ 22
2.3.5.2 Energy consumption of pre-treatment and post-treatment ......................................... 23

iv
2.3.5.3 Integration into system-scale model ............................................................................ 24
2.3.5.4 Composition of net SEC .............................................................................................. 25
2.3.5.5 Specific energy comparison for select conditions of four scenarios ........................... 26
2.3.6 Summary for select conditions of four scenarios ................................................................ 27
2.4 Conclusion and implication ......................................................................................................... 28
Acknowledgement ................................................................................................................................... 29
3 CHAPTER 3. Potable Reuse of Reclaimed Wastewater with Increasing Salinity: Water Recovery and
Energy Consumption ................................................................................................................................... 30
Abstract.................................................................................................................................................... 30
3.1 Introduction .................................................................................................................................. 31
3.1.1 Role of desalination in water reuse ..................................................................................... 32
3.1.2 Higher-salinity streams examples ....................................................................................... 33
3.1.3 Energy and water recovery by energy recovery devices and high-recovery RO ................ 34
3.1.4 Previous work and objectives .............................................................................................. 35
3.2 Methodology ................................................................................................................................ 36
3.2.1 Flowrates and salinities of treated wastewater, intruded seawater, and higher-salinity
streams 36
3.2.2 Modeling framework ............................................................................................................ 38
3.2.3 Inorganic scaling potential considering seawater I&I and higher-salinity streams .............. 40
3.3 Results and discussion ............................................................................................................... 41
3.3.1 Effect of seawater I&I and higher-salinity streams on 𝑆𝐸𝐶
𝑁𝑒𝑡 ............................................. 41
3.3.2 𝑆𝐸𝐶
𝑁𝑒𝑡 when using an RO-ERD .......................................................................................... 42
3.3.3 𝑆𝐸𝐶
𝑁𝑒𝑡 when using CCRO ................................................................................................... 44
3.3.4 𝑆𝐸𝐶
𝑁𝑒𝑡 when desalinating higher-salinity streams separately from the treated wastewater
46
3.3.5 𝑆𝐸𝐶
𝑁𝑒𝑡 comparison of three energy saving strategies ........................................................ 49
3.3.6 Inorganic scaling potential considering seawater I&I and higher-salinity streams .............. 50
3.3.7 Permeate and brine water quality ....................................................................................... 51
3.3.8 Implications ......................................................................................................................... 51
Acknowledgement ................................................................................................................................ 52
4 CHAPTER 4. Theoretical and Practical Energy Consumption when Treating Higher-Salinity
Wastewaters for Potable Reuse ................................................................................................................. 54
4.1 Introduction .................................................................................................................................. 54
4.1.1 Increasing salinity at AWPFs – treatment by RO ................................................................ 54
4.1.2 Energy and water recovery by energy recovery devices and high-recovery RO ................ 54
4.2 Objectives .................................................................................................................................... 55
4.3 Material and methods .................................................................................................................. 57
4.3.1 Modeling system ................................................................................................................. 57
4.3.2 Thermodynamic energy efficiency for the RO process ....................................................... 57

v
4.3.3 Minimum specific energy consumption for the RO process ................................................ 58
4.3.4 Practical specific energy consumption of RO calculated by WAVE software and its
comparison between theoretical minimum specific energy consumption of RO ................................. 58
4.4 Results and discussions .............................................................................................................. 59
4.4.1 Thermodynamic energy efficiency comparison between RO alone, RO-ERD, and CCRO 59
4.4.2 RO minimum specific energy consumption between RO alone, RO-ERD, and CCRO ...... 61
4.4.3 Salinity related and non-salinity related non-idealities between 𝑆𝐸𝐶
𝑅𝑂 ,𝑚𝑖𝑛 and 𝑆𝐸𝐶
𝑅𝑂 ,𝑊𝐴𝑉𝐸 63
4.5 Implications ................................................................................................................................. 64
5 CHAPTER 5. Conclusions ................................................................................................................... 66
5.1 Research synopsis ...................................................................................................................... 66
5.2 Major contributions ...................................................................................................................... 66
5.2.1 Summary of modeling framework to evaluate blending of seawater and treated wastewater
streams for synergistic desalination and potable reuse ....................................................................... 66
5.2.2 Summary of potable reuse treatment of reclaimed wastewater with increasing salinity ..... 67
5.2.3 Summary of energy consumptions for seawater augmented advanced water purification
facilities 68
5.3 Impacts and implications ............................................................................................................. 69
6 Appendix A: Supplementary Information ............................................................................................. 70
A.1 Supplementary Information to Chapter 2 .......................................................................................... 70
A.1.1 Scenarios description ................................................................................................................. 70
A.1.2 Energy consumption of pre-treatment ........................................................................................ 72
A.2 Supplementary Information to Chapter 3 .......................................................................................... 74
A.2.1 Selection of RO advanced water purification facilities in California and whether or not an
energy recovery device is used ........................................................................................................... 74
A.2.2 Salinities of secondary effluents serving as influent for selected advanced water purification
facilities ................................................................................................................................................ 75
A.2.3 Rate of 𝑆𝐸𝐶
𝑁𝑒𝑡 change of introducing higher-salinity streams ................................................... 76
A.2.4 Flowrates, energy consumption, and permeate and brine salinities when using high-recovery
RO with water-recovery of 95% ........................................................................................................... 77
A.2.5 RO water-recovery rates for treated wastewater and higher-salinity streams for separate
desalination .......................................................................................................................................... 80
A.2.5 Feed LSI when desalinating treated wastewater and higher-salinity streams together and
separately ............................................................................................................................................ 81
A.2.7 Water quality of treated wastewater, seawater and higher-salinity streams .............................. 82
A.2.8 Summary of permeate and brine salinities ................................................................................. 83
A.3 Supplementary Information to Chapter 4 .......................................................................................... 86
A.3.1 Summary of comparisons between 𝑆𝐸𝐶
𝑅𝑂 ,𝑚𝑖𝑛 , 𝑆𝐸𝐶
𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑖𝑛 , and 𝑆𝐸𝐶
𝐶𝐶𝑅𝑂 ,𝑚𝑖𝑛 ....................... 86
References .................................................................................................................................................. 87

vi
List of Figures
Figure 1-1 Water supply system with desalination and potable water reuse (a) Current water supply
system; (b) Propsed water system in this dissertation. ............................................................... 6
Figure 2-1 Schematic of coastal water system. .......................................................................................... 10
Figure 2-2 Four scenarios to evaluate synergistic use of SWRO brine and treated wastewater streams. 12
Figure 2-3 RO influent flowrate requirements to achieve desired product water flowrate of 1.14 × 10
4
m
3
/d
for seawater:treated wastewater (SW:WW) influent ratios. ...................................................... 16
Figure 2-4 RO brine salinity for seawater:treated wastewater (SW:WW) influent ratios. The horizontal line
indicates the limitation for discharge salinity (40 g/L) set in the current study. Operation at
SW:WW influent ratios of 40:60 or greater require discharge blending to meet the salinity limit;
operation at SW:WW influent ratios of 30:70 or less does not require discharge blending. ..... 18
Figure 2-5 Required treated wastewater flowrates for both influent dilution and discharge dilution for all
seawater:treated wastewater (SW:WW) influent ratios in (a) Scenarios 1 and 2 (the brine
blending scenarios), (b) Scenario 3 – the influent blending scenario, and (c) Scenario 4 – the
influent blending scenario with osmotic dilution. The horizontal line in Scenario 3 (Figure 2-5b)
indicates the available amount of treated wastewater in the current study. ............................. 19
Figure 2-6 Discharge flowrates for seawater:treated wastewater (SW:WW) influent ratios in (a) Scenarios
1 and 2 (b) Scenario 3, (c) Scenario 4. ..................................................................................... 21
Figure 2-7 Boron concentration in RO permeate for seawater:treated wastewater (SW:WW) influent
ratios. ......................................................................................................................................... 22
Figure 2-8 RO specific energy consumption for seawater:treated wastewater (SW:WW) influent ratios... 23
Figure 2-9 Net SEC comparison for seawater:treated wastewater (SW:WW) influent ratios in four
scenarios. .................................................................................................................................. 25
Figure 2-10 Percentage of RO, UF, UV/ H2O2, and forward osmosis (FO) in net SEC for seawater:treated
wastewater (SW:WW) influent ratios in (a) Scenario 1, (b) Scenario 2, (c) Scenario 3, and (d)
Scenario 4. ................................................................................................................................ 26
Figure 2-11 RO, UF, UV/H2O2, and forward osmosis (FO) specific energy consumptions, and pressure-
retarded osmosis (PRO) and ERD specific energy savings for Scenarios 1-4. The net SEC is
calculated by subtracting total SES from total SEC. ................................................................. 27
Figure 2-12 RO, UF, UV/H2O2, and forward osmosis (FO) specific energy consumptions, and pressure-
retarded osmosis (PRO) and ERD specific energy savings for Scenarios 1-4. ........................ 28
Figure 3-1 Diagrams for (a) two-stage RO, (b) two-stage RO with an energy recovery device, and (c)
closed-circuit RO. ...................................................................................................................... 34
Figure 3-2 Schematic of flowrates and salinities for the wastewater, intruded seawater, and higher-salinity
streams entering an advanced water purification facility. X represents the percentage of
seawater I&I; a represents the salinity of the higher-salinity stream; b represents the influent
salinity to the advanced water purification facility (see Table 3-1); c and d represent the
resulting salinities of the RO permeate and brine streams. There are two possible blending
points for the higher-salinity streams (points 1 and 2), selection of which depends on the water
quality of the higher-salinity stream. Because wastewater treatment processes generally do
not decrease salinity, the choice of blending point does not affect salinity values b, c, and d. 38
Figure 3-3 𝑆𝐸 𝐶 𝑁𝑒𝑡 without and with higher-salinity streams for the five seawater I&I scenarios. The first bar
in each group represents the 𝑆𝐸𝐶
𝑁𝑒𝑡 for advanced water purification facilities without adding
higher-salinity streams (the base case). The other four bars in each group represent the
𝑆𝐸𝐶
𝑁𝑒𝑡 for advanced water purification facilities with higher-salinity streams. The red horizontal
lines represent the base case 𝑆𝐸𝐶
𝑁𝑒𝑡 for each group and the black dots represent the influent
salinity. All values are for systems without ERDs or CCRO. .................................................... 42
Figure 3-4 𝑆𝐸𝐶
𝑁𝑒𝑡 without and with higher-salinity streams for the five seawater I&I scenarios. Bars are
paired with the left-hand bar representing 𝑆𝐸𝐶
𝑁𝑒𝑡 for advanced water purification facilities
without an ERD and the right-hand bar representing 𝑆𝐸𝐶
𝑁𝑒𝑡 for facilities with an ERD. The
difference between the left-hand and right-hand bars represents the energy savings from an
ERD. The first pair of bars in each group represents 𝑆𝐸𝐶
𝑁𝑒𝑡 for the base case of each group

vii
and the red horizontal line allows comparison of the base case of each group with the higher-
salinity cases. The black dots represent influent salinity for each pair. .................................... 44
Figure 3-5 𝑆𝐸𝐶
𝑁𝑒𝑡 without and with higher-salinity streams for the five seawater I&I scenarios. Bars are
paired with the left-hand bar representing 𝑆𝐸𝐶
𝑁𝑒𝑡 for advanced water purification facilities
using regular RO and the right-hand bar representing the 𝑆𝐸𝐶
𝑁𝑒𝑡 for advanced water
purification facilities using CCRO. The difference between the left-hand and right-hand bars
represents the energy savings from CCRO. The first pair of bars in each group represents the
𝑆𝐸𝐶
𝑁𝑒𝑡 for the base case of each group and the red horizontal line allows comparison of the
base case of each group with other cases that represent addition of higher-salinity streams.
The black dots represent influent salinity for each pair. ............................................................ 46
Figure 3-6 𝑆𝐸𝐶
𝑁𝑒𝑡 when desalinating treated wastewater and higher-salinity streams together and
separately for the five seawater I&I scenarios. Bars are paired with the left-hand bar
representing the 𝑆𝐸𝐶
𝑁𝑒𝑡 for advanced water purification facilities when desalinating treated
wastewater and higher-salinity streams together and the right-hand bar representing the
𝑆𝐸𝐶
𝑁𝑒𝑡 for advanced water purification facilities when desalinating higher-salinity streams
separately from treated wastewater. There is no right-hand bar for the base case because
there is no stream to desalinate separately. The difference between the left-hand and right-
hand bars represents the energy savings from separate desalination. The first bar in each
group represents the 𝑆𝐸𝐶
𝑁𝑒𝑡 for the base case and the red horizontal line allows comparison of
the base case of each group with other cases that represent addition of higher-salinity
streams. The black dots represent the salinity difference between the higher-salinity stream
and treated wastewater. ............................................................................................................ 48
Figure 3-7 Comparison of 𝑆𝐸𝐶
𝑁𝑒𝑡 of three energy-saving strategies for a) regional brine interceptor, b)
BWRO brine 1, c) BWRO brine 2, and d) BWRO brine 3. The 𝑆𝐸𝐶
𝑁𝑒𝑡 of three energy-saving
strategies, including RO-ERD, CCRO, and desalinating higher-salinity streams separately are
compared with 𝑆𝐸𝐶
𝑁𝑒𝑡 of using RO alone. ................................................................................ 50
Figure 4-1 (a) Theoretical maximum thermodynamic energy efficiency as a function of RO water-recovery
(adapted from Lin et al.(Lin, 2020)) and (b) theoretical maximum thermodynamic energy
efficiency as a function of salinity for scenarios using CCRO, RO-ERD, and RO alone. Figure
4-1 (b) is adapted from Figure 4a with the following assumptions: 85% water recovery for
AWPF RO (with 1.2 g/L as feed salinity), 50% water recovery for SWRO (with 34.4 g/L as feed
salinity) (Wei et al., 2020), and a linear relationship between feed salinity and water recovery.
.................................................................................................................................................. 60
Figure 4-2 Comparison of 𝑆𝐸𝐶
𝑚𝑖𝑛 of three configurations for a) RO alone, b) RO-ERD and c) CCRO with
water-recovery rates ranging from 5 to 95% and salinities ranging from 0 to 40 g/L. The
contour lines indicated all points of which are at the same 𝑆𝐸𝐶
𝑚𝑖𝑛 values. Both the color of the
contour line and the number labeled on the contour line indicated the value of 𝑆𝐸𝐶
𝑚𝑖𝑛
representing a specific line. ....................................................................................................... 62
Figure 4-3 Comparison of 𝑆𝐸𝐶
𝑅𝑂
calculated by WAVE design software with 𝑆𝐸𝐶
𝑅𝑂 ,𝑚𝑖𝑛 enables clear
identification of regions where salinity-related non-idealities and non-salinity related non-
idealities result in modeled SEC being greater than theoretical minimum SEC. Also shown are
two regions below the 𝑆𝐸𝐶
𝑅 𝑂 ,𝑚𝑖𝑛 line that indicate where implementation of an ERD or
transition to high-recovery RO (e.g., CCRO) enables removal of additional salinity with no
additional energy consumption. The horizontal lines representing 0.47 and 3.2 g/L are
measures of energy-free desalination of higher-salinity streams by using ERD-RO or CCRO.
.................................................................................................................................................. 64

Figure A.1.1 Scenario 1 (baseline scenario) – blending treated wastewater with RO brine. ..................... 71
Figure A.1.2 Scenario 2 – blending treated wastewater with RO brine and extracting salinity-gradient
energy. ................................................................................................................................... 71
Figure A.1.3 Scenario 3 – blending treated wastewater with seawater influent. ........................................ 72
Figure A.1.4 Scenario 4 – blending treated wastewater with seawater influent using osmotic dilution...... 72
Figure A.1.5 UF energy consumption for pre-treatment as a function of seawater:treated wastewater
(SW:WW) influent ratios. ........................................................................................................ 73

viii
Figure A.2.1 Rate of 𝑆𝐸𝐶
𝑁𝑒𝑡 change of introducing four types of higher-salinity streams for the five
seawater I&I scenarios. .......................................................................................................... 76
Figure A.2,2 𝑆𝐸𝐶
𝑁𝑒𝑡 with higher-salinity streams for the five seawater I&I scenarios when using CCRO
with water-recovery of 85% and 95%. The first two bars in each group represents the 𝑆𝐸𝐶
𝑁𝑒𝑡
for AWPFs without adding higher-salinity streams. Every two bars are grouped together. The
left bar and right bar represent the 𝑆𝐸𝐶
𝑁𝑒𝑡 for AWPFs with water-recovery rate of 85% and
95%. The other eight bars in each group represent the 𝑆𝐸𝐶
𝑁𝑒𝑡 for AWPFs with higher-salinity
streams. ................................................................................................................................. 78
Figure A.2.3 Permeate (Figure A.2.3a) and brine (Figure A.2.3b) salinity without and with higher-salinity
streams for the five seawater I&I scenarios when using regular RO (with water-recovery of
85%) and high-recovery RO (with water-recovery of 95%). The first two bars in each group
represents the permeate salinity for AWPFs without adding higher-salinity streams. Every
two bars are grouped together. The left bar and right bar represent the permeate salinity for
AWPFs when using regular and high-recovery RO. The other eight bars in each group
represent the permeate salinity for AWPFs with higher-salinity streams. ............................. 78
Figure A.2.4 Schematic of flowrates and salinities for the wastewater, intruded seawater, and higher-
salinity streams entering an advanced water purification facility with high-recovery RO. The
water recovery for high-recovery RO is set to 95%. X represents the percentage of seawater
I&I; a represents the salinity of the higher-salinity stream; b represents the influent salinity to
the advanced water purification facility; c and d represent the resulting salinities of the RO
permeate and brine. There are two possible blending points for the higher-salinity streams
(points 1 and 2), selection of which depends on the water quality of the higher-salinity
stream. Because wastewater treatment processes generally do not decrease salinity, the
choice of blending point does not affect salinity values b, c, and d. ...................................... 79
Figure A.2.5 Permeate (Figure A.2.5a) and brine (Figure A.2.5b) salinity without and with higher-salinity
streams for the five seawater I&I scenarios when using regular RO. .................................... 84

ix
List of Tables

Table 3-1 Salinities of the advanced water purification facility influent for all scenarios considered. The 25
values shown in the table are used as the b value in Figure 3-2. .............................................. 38

Table A.2.1 Summary of RO advanced water purification facilities in California and whether or not an
energy recovery device (ERD) is used .................................................................................... 74
Table A.2.2 Example Water Treatment Facilities Producing Water of Potable Reuse Quality .................. 75
Table A.2.3 RO water-recovery rates for treated wastewater and higher-salinity streams with lowest
𝑆𝐸𝐶
𝑁𝑒𝑡 when desalinating higher-salinity streams separately from treated wastewater. ........ 80
Table A.2.4 Feed LSI when desalinating treated wastewater and higher-salinity streams and desalinating
both streams separately. ......................................................................................................... 81
Table A.2.5 Water quality of treated wastewater, seawater and higher-salinity streams ........................... 82
Table A.2.6 Summary of permeate salinities with and without higher-salinity streams in influent ............. 83
Table A.2.7 Summary of brine salinities with and without higher-salinity streams in influent ..................... 83

Table A.3.1 Summary of comparisons between 𝑆𝐸𝐶
𝑅𝑃 ,𝑚𝑖𝑛 , 𝑆𝐸𝐶
𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑖𝑛 , and 𝑆𝐸𝐶
𝐶𝐶𝑅𝑂 ,𝑚𝑖𝑛 ..................... 86

x
Abstract
Water scarcity, a critical environmental issue globally, has primarily been driven by a
significant increase in surface water and groundwater extractions due to increased global
population, rising standards of living, and climate and societal changes. With the emergence of
new technologies, alternative water sources supplied by wastewater reclamation, seawater
desalination, and brackish water desalination are in rapid development. Wastewater reclamation
and desalination provide independent supplies of water that can be cost-competitive and more
reliable than importing/transferring water from other regions or collecting and treating
stormwater runoff. Reclaimed wastewater and desalinated water undergo separate treatment
and transport and are often not seen as the interconnected water resources that they are.
Particularly in coastal water-scarce regions, where surface water sources have limited
availability and groundwater sources may be fully allocated, wastewater reclamation and
seawater desalination are important components of water supply portfolios. The main objective
of this dissertation is to investigate synergistic systems for desalination and potable reuse and
understand the impact of novel configurations on energy consumption and water recovery.
Firstly, to investigate the synergistic blending opportunities of the waste streams from seawater
reverse osmosis (RO) and wastewater treatment facilities, four scenarios – two discharge
blending and two influent blending – were considered. A modeling framework was developed
based on seawater RO facilities to evaluate required seawater and treated wastewater
flowrates, discharge flowrates and components, boron removal, and system energy
requirements. The best blending scenario to meet seawater RO brine discharge requirements
was determined. Secondly, to critically evaluate the energy that will be consumed in recovery
water from higher-salinity streams for additional influents at advanced water purification
facilities, the benefits of additional influents are weighted against the additional energy
consumption due to increased salinity in the influent. Opportunities to implement or enhance

xi
energy and water recovery using an energy recovery device in conjunction with RO or by using
closed-circuit RO are considered. Also, a scenario of desalinating higher-salinity streams
separately from treated wastewater is considered. Thirdly, to understand the energy
consumption during potable reuse of higher-salinity streams, both theoretical minimum energy
consumption and practical energy consumption are analyzed to compare energy consumption
when using ERDs in conjunction with RO, and using high-recovery RO (e.g., closed-circuit RO)
with a baseline. In addition, the theoretical minimum energy consumption of RO is compared
with the practical energy consumptions to investigate the inefficiencies that can be targeted to
bring the practical energy consumption closer to the theoretical energy consumption of RO.

1
CHAPTER 1.

1.1 Introduction
Water scarcity, a critical environmental issue globally, has primarily been driven by a
significant increase in surface water and groundwater extractions due to increased global
population, rising standards of living, and climate and societal changes (Greve et al., 2018;
Veldkamp et al., 2017). With the emergence of new technologies, alternative water sources
supplied by wastewater reclamation, seawater desalination, and brackish water desalination are
in rapid development (Gude, 2017). Wastewater reclamation and desalination provide
independent supplies of water that can be cost-competitive and more reliable than
importing/transferring water from other regions or collecting and treating stormwater runoff.
Reclaimed wastewater and desalinated water undergo separate treatment and transport and
are often not seen as the interconnected water resources that they are.
Particularly in coastal water-scarce regions, where surface water sources have limited
availability and groundwater sources may be fully allocated, wastewater reclamation and
seawater desalination are important components of water supply portfolios. For example, in
Australia, in response to drought, several desalination facilities were built between 1960 and
1980 (Mekonnen and Hoekstra, 2016; Radcliffe and Page, 2020). The millennium drought from
2000 to 2009 further drives desalination in Australia (Radcliffe and Page, 2020). In 2019,
Western Australia began to explore the recycling approach through groundwater replenishment
and the project is in full operation in Perth (Radcliffe and Page, 2020). In Singapore, an island-
country, there are limited water resources and dense population. Since 2003, Singapore has
implemented five NEWater facilities that reclaim wastewater mostly for high-quality industrial
use but also for indirect potable reuse via reservoir augmentation (International Water
Association, 2020) The five NEWater facilities were commissioned at Bedok (2003), Kranji

2
(2003), Seletar (2004), Ulu Pandan (2007), and Changi (2010) (Chew et al., 2011). Since 2005,
four seawater desalination facilities were built in Singapore and the fifth will be ready in 2021
(Singapore National Water Agency, 2021a). In Israel, high-quality non-potable water reuse for
agriculture started in 1978 (Leusch and Snyder, 2015), and large-scale seawater desalination
plants within the national water supply system was drafted back to 1997 and now continuously
and reliably supply potable water (Tenne et al., 2013). Currently, there are five desalination facilities
are in operation in Israel, locating in Ashkelon, Sorek, Hadera, Palmachim, and Adhdod (Kenigsberg et
al., 2020; Tenne et al., 2013). Although the US is considered to be a water-rich country, uneven
distribution causes some areas of the country, including California, Texas, and Florida, to face severe
water supply issues (Gude, 2017; Jones and van Vliet, 2018). In the US, California is leading with the
highest number of potable reuse projects and more than 50 years’ experience and Arizona, Colorado,
Texas, and Virginia have demonstration or full-scale potable projects (Meridian Institute and Paradigm
Environmental, 2018). The potable reuse projects in the US have been supported by the communities
and they follow the federal and state regulations on potable reuse (Meridian Institute and Paradigm
Environmental, 2018; Rodriguez et al., 2009).

1.2 Background
1.2.1 Wastewater potable reuse
Reclaimed wastewater is used in both indirect potable reuse (IPR) and direct potable
reuse (DPR) scenarios. Except for the DPR project in Big Spring, TX, all existing potable reuse
systems in the US are IPR (Nix et al., 2021). IPR is typically preferred over DPR because
indirect scenarios often utilize an environmental storage buffer (e.g., a groundwater aquifer or a
surface water reservoir) that provides: (1) dilution, (2) storage, (3) response time in case of
treatment failures or upsets, (4) and additional opportunity for removal and attenuation of
microbial and chemical contaminants (WateReuse Project, 2015). For example, in the case of
groundwater recharge, when reclaimed wastewater is injected into or sprayed across the

3
ground surface, in-situ treatment via filtration and adsorption can occur during transport through
the subsurface. In surface water augmentation, when reclaimed wastewater is discharged to a
lake or reservoir, the reclaimed wastewater may undergo some additional treatment from
exposure to sunlight (UV light) but the main benefit is dilution and additional detention/response
time (Soller et al., 2019).
Although there are several advantages to having an environmental storage buffer, there
can also be disadvantages. For example, if the final product water from the treatment facility is
blended with a lower quality surface water or groundwater, then the highly-treated reuse water
may be contaminated (Leverenz et al., 2011). In this situation, or if an environmental storage
buffer is not available, an engineered storage buffer (e.g., a tank or system of tanks) provides
another IPR option. The advantages of an environmental storage buffer over an engineered
storage buffer is that it offers a controlled environment that is not likely to contaminate the reuse
water. Also, evaporation losses are prevented (Leverenz et al., 2011). The disadvantages of an
environmental storage buffer are that there is no in-situ treatment or exposure to sunlight and
the reuse water is not available to recharge a groundwater aquifer.
If there is no availability of a groundwater aquifer or surface water reservoir and there is
no space or budget for an engineered storage buffer, DPR is an option. In DPR, advanced
purified water can be combined with natural raw water supply to a conventional drinking water
treatment facility; this scenario is raw water augmentation. RWA is a more conservative
approach to direct potable reuse than treated water augmentation. Treated water augmentation
refers to the planned placement of recycled water directly into a finished water distribution
system of a public water system. In California, state permitting requirements are currently being
established for RWA and TWA and are expected by the end of 2023 (Pecson et al., 2020).
1.2.2 Seawater desalination
Among all seawater desalination technologies, reverse osmosis (RO) is the most
predominant one (Amy et al., 2017; Greenlee et al., 2009). Although concerns with trace organic

4
compounds and other contaminants of emerging concern are much lower when desalinating
seawater, there are often very stringent environmental regulations that must be met (State
Water Resources Control Board, 2019). For example, in California, the Ocean Plan “requires
new or expanded seawater desalination plants to use the best available site, design,
technology, and mitigation measures feasible to minimize intake and mortality of all forms of
marine life” (State Water Resources Control Board, 2019).
1.2.3 Similarities between potable reuse and SWRO treatment trains
An industry standard IPR treatment train includes: membrane filtration (MF, referring to
microfiltration or ultrafiltration (UF)), RO, and UV/H2O2 (Holloway et al., 2016; Pecson et al.,
2017). For DPR, where dilution, detention/response time, and additional treatment is not
available in the environmental or engineered storage buffer, it is proposed to add Ozone-
Biological Activated Carbon (O3/BAC) prior to MF, RO, and UV/H2O2 (Chuang et al., 2019). BAC
is used to simultaneously adsorbed and biodegrade organic compounds (Jin et al., 2013). O3 is
commonly used as an oxidant prior to BAC in potable reuse trains to target refractory organics,
especially precursors of disinfection by-products (Chuang and Mitch, 2017; Jin et al., 2013).
In comparing the IPR treatment train with a traditional SWRO treatment train (MF/UF-
RO-UV/AOP) (Wei et al., 2020), there are many similarities, including that the most energy-
intensive process for both is RO (Elimelech and Phillip, 2011; Holloway et al., 2016). As
treatment-plant influents have become more saline, desalination by RO in advanced water
purification facilities (AWPFs) has become important. Hence, while the role of RO membranes
in separating pathogens and trace organic compounds is still key, the role of RO membranes in
separating salts in potable reuse is being rediscovered as critical.

1.3 Objectives
The main objective of this dissertation is to investigate synergistic systems for
desalination and potable reuse (Figure 1-1) and understand the impact of the novel

5
configurations on energy consumption and water recovery. Firstly, to investigate the synergistic
blending opportunities of the waste streams from SWRO and wastewater treatment facilities,
four scenarios – two discharge blending and two influent blending – were considered. A
modeling framework was developed based on SWRO facilities to evaluate required seawater
and treated wastewater flowrates, discharge flowrates and components, boron removal, and
system energy requirements. The best blending scenario to meet SWRO brine discharge
requirements was determined. Secondly, to critically evaluate the energy that will be consumed
in recovery water from higher-salinity streams for additional influents at advanced water
purification facilities, the benefits of additional influents are weighted against the additional
energy consumption due to increased salinity in the influent. Opportunities to implement or
enhance energy and water recovery using an energy recovery device (ERD), an interstage
pump between RO stages, and high-recovery RO are considered. Also, a scenario of treating
higher-salinity streams and treated wastewater in separate RO trains is considered. This study
aims to nominate the most suitable design for desalination systems pursuing hi water- and
energy-recovery objectives under different situations. Thirdly, to understand the energy
consumption during potable reuse of higher-salinity streams, three scenarios, 1) using RO
alone, 2) using ERDs in conjunction with RO, and 3) using HRRO instead of RO are considered.
In addition, the theoretical minimum energy consumptions of RO are compared with the
practical energy consumptions to quantify the gap between theoretical minimum energy
consumption and practical energy consumption of RO over a range of salinities and to delineate
what the gaps are attributed to. Furthermore, the inefficiencies that are salinity-related are
distinguished from those that are not salinity-related, which provides insight into how to bring the
practical energy consumption closer to the theoretical energy consumption of RO. This research
also builds on theoretical work that has been published regarding implementation of ERDs and
HRRO and seeks to bridge the gap between these studies and actual desalination systems
pursuing high water and energy recovery objectives.

6

Figure 1-1 Water supply system with desalination and potable water reuse (a) Current water supply system; (b)
Propsed water system in this dissertation.

1.4 Dissertation organization
The dissertation is a compilation of three papers written over the courses of dissertation
research. Chapter 2 is an entire paper manuscript that was published in the Water Research
journal. Chapter 3 has been submitted to Environmental Science & Technology journal and is
under revision. Chapter 4 is a draft manuscript for a paper in the final stages of preparation.

7
2 CHAPTER 2. A Modeling Framework to Evaluate Blending
of Seawater and Treated Wastewater Streams for
Synergistic Desalination and Potable Reuse

Reprinted (adapted) with permission from X. Wei, Z.M. Binger, A. Achilli, K.T. Sanders, and A.E. Childress, “A
modeling framework to evaluate blending of seawater and treated wastewater streams for synergistic
desalination and potable reuse”, Water Research, vol. 170, p. 115282, 2020. Copyright 2019 Elsevier. (Wei et
al., 2020)

Abstract
A modeling framework was developed to evaluate synergistic blending of the waste
streams from seawater reverse osmosis (RO) desalination and wastewater treatment facilities
that are co-located or in close proximity. Four scenarios were considered, two of which involved
blending treated wastewater with the brine resulting from the seawater RO desalination process,
effectively diluting RO brine prior to discharge. One of these scenarios considers the capture of
salinity-gradient energy. The other two scenarios involved blending treated wastewater with the
intake seawater to dilute the influent to the RO process. One of these scenarios incorporates a
low-energy osmotic dilution process to provide high-quality pre-treatment for the wastewater.
The modeling framework evaluates required seawater and treated wastewater flowrates,
discharge flowrates and components, boron removal, and system energy requirements. Using
data from operating facilities, results showed that the two influent blending scenarios (Scenarios
3 and 4) had several advantages over the RO brine blending scenarios (Scenarios 1 and 2),
including: 1) reduced seawater intake and brine discharge flowrates, 2) no need for second-
pass RO targeting boron control, and 3) reduced energy consumption. It should be noted that
the framework was developed for use with co-located seawater desalination and coastal
wastewater reclamation facilities but could be extended for use with desalination and
wastewater reclamation facilities in in-land locations where disposal of RO concentrate is a
serious concern.

8
2.1 Introduction and background
2.1.1 Seawater reverse osmosis desalination
As of 2018, there were 5,328 operational seawater desalination plants with a total global
desalination capacity of approximately 58 million m
3
/day (Jones et al., 2019). Of the seawater
desalination technologies, reverse osmosis (RO) is the most dominant process (Amy et al.,
2017; Greenlee et al., 2009), producing 56% of the global seawater desalination product (Jones
et al., 2019). Although RO is the most widely adopted commercial seawater desalination
technology, seawater RO (SWRO) has several drawbacks, including that it produces a brine
stream, requires seawater intakes, and has high energy requirements.
Global brine production by SWRO in 2018 was approximately 44 million m
3
/day, or 16.0
billion m
3
/year (Jones et al., 2019). The discharge of RO brine into ocean environments can
have ecosystem impacts. Because of its high density, contaminants can be carried to the ocean
floor where benthic organisms may be harmed because there is minimal wave propagation for
mixing and dilution (Tularam and Ilahee, 2007). In some countries (e.g., USA, Australia, Japan,
UAE, and Oman), dilution and/or diffusers are required prior to/during the discharge of RO brine
to the ocean (Jenkins et al. 2012) to reduce and attenuate brine concentration.
Entrainment and impingement of marine organisms by seawater intake systems is also a
major environmental concern (Missimer and Maliva, 2018). Subsurface intakes can be used to
mitigate the effects of intake systems on aquatic communities (Henthome and Boysen, 2015).
Because subsurface intakes also provide some pre-treatment, their use in small systems may
be beneficial; however, for large systems, their installation significantly increases capital costs
and construction time (Missimer et al., 2013). Additionally, the installation of subsurface intakes
depends on the presence of proper geology and sediment characteristics such as sand and
gravel with sufficiently high porosity and transmissivity (Missimer and Maliva, 2018).
In addition to these concerns, there are also concerns with the high energy requirement
of SWRO. Although RO is the most energy efficient commercial seawater desalination

9
technology, it still requires a relatively high amount of energy to achieve the pressures
necessary to overcome the osmotic pressure of seawater (Elimelech and Phillip, 2011; Lin and
Elimelech, 2015). Energy recovery devices (ERDs) with efficiencies greater than 95% are
commonplace and reduce energy consumption by as much as 60% (Penate and Garcia-
Rodriguez, 2011). With ERDs, current state-of-the-art SWRO facilities consume between 3 and
3.5 kWh/m
3
(Ng et al., 2015).
If second-pass RO is required for boron removal, energy consumption increases further.
Typically, boron concentrations in seawater are approximately 4-6 mg/L (Park et al., 2012) and
SWRO only rejects approximately 83-92% (Shultz and Freger, 2018). States such as California
and Florida, and countries such as Israel, Saudi Arabia, and Japan have regulations or
guidelines for maximum boron levels ranging from 0.4 to 1 mg/L. For example, the California
State Notification Level is 1 mg/L. Thus, second-pass RO for all or part of the first-pass product
water may be required (Alnouri and Linke, 2014; Du et al., 2016; Du et al., 2015; Sassi and
Mujtaba, 2013).
2.1.2 Synergistic opportunities in coastal water system
SWRO facilities may be co-located with wastewater treatment facilities that also
discharge a stream to the ocean. Currently, the only synergistic use of these waste streams is to
use the treated wastewater to dilute the SWRO brine stream prior to discharge (Figure 2-1). The
2015 Amendment to California Ocean Plan (California Environmental Protection Agency, 2019)
defines this blending as the preferred technology, with the goal being that the resulting blended
solution is positively buoyant (Voutchkov, 2011). In this way, the supply of treated wastewater
could define the amount of seawater that can be desalinated. However, discharge of treated
wastewater to the ocean could be considered a waste of the water resource within this stream.

10

Figure 2-1 Schematic of coastal water system.
Instead of using treated wastewater to dilute the RO brine, a possible future scenario is
to blend the treated wastewater (after additional advanced treatment processes) with the intake
seawater. By blending the treated wastewater with the intake seawater upstream of the RO, not
only will the SWRO feed be diluted, but the SWRO brine will also be more dilute. This scenario
represents a raw water augmentation approach to direct potable reuse of treated wastewater
(National Water Research Institute, 2018) and has been considered briefly in the literature (Cath
et al., 2005; Hancock et al., 2012; Hancock et al., 2013; Linares et al., 2016; Shaffer et al.,
2012).
The objective of the current study is to evaluate synergistic blending of the waste
streams from SWRO and wastewater treatment facilities. Four scenarios – two discharge
blending and two influent blending – were considered. A modeling framework was developed to
evaluate required seawater and treated wastewater flowrates, discharge flowrates and
components, boron removal, and system energy requirements. The best blending scenario to
meet SWRO brine discharge requirements was determined.

11

2.2 Material and methods
2.2.1 System model framework
All scenarios were modeled based on a medium-size 1.14  10
4
m
3
/d (3 million
gallons/day (MGD)) SWRO facility, the Charles E. Meyer Desalination Plant (Santa Barbara,
CA) and a 3.03  10
4
m
3
/d (8 MGD) secondary wastewater treatment facility, the El Estero
Wastewater Treatment Plant (Santa Barbara, CA), which are 0.2 km apart. Approximately half
of the treated wastewater (1.63  10
4
m
3
/d) is further treated with tertiary processes to provide
non-potable reuse water. The other half of the treated wastewater (1.40  10
4
m
3
/d) is used to
dilute the brine from the SWRO facility. The blended stream is discharged into a pipeline that
extends 2.4 km into the ocean.
Brine discharge regulations that exist around the world range from salinity increments
above ambient (e.g., 1 part per thousand (ppt)) to absolute levels (e.g., 40 g/L) (Jenkins et al.,
2012). These limits typically apply at the boundary of a mixing zone that has dimensions on the
order of 50 to 300 m surrounding the discharge (Jenkins et al., 2012). The 2015 Amendment to
California Ocean Plan (California Environmental Protection Agency, 2019) states that
discharges to the receiving water body shall not exceed a daily maximum of 2 ppt above the
natural background salinity measured no further than 100 m horizontally from the discharge
point. Accordingly, the Claude “Bud” Lewis Carlsbad desalination facility in Carlsbad, CA and a
new facility in late-stage permitting in Huntington Beach, CA have absolute limits of less than 40
ppt at a compliance point of 305 m (1000 ft) from the discharge location. In the current
framework, the limitation for discharge salinity was set at 40 g/L.
2.2.2 Overview of scenarios
This section provides an overview of the four scenarios considered (Figure 2-2). Detailed
discussion and depiction of the scenarios can be found in Supplementary Information (Figs. S.1

12
- S.4). The scenarios included a brine blending scenario (blending treated wastewater with RO
brine) (Figure 2-2a), a scenario with extraction of salinity gradient energy during brine blending
(Figure 2-2b), an influent blending scenario (blending treated wastewater with seawater influent
to RO) (Figure 2-2c), and a scenario with osmotic dilution as a treatment process during influent
blending (Figure 2-2d).

Figure 2-2 Four scenarios to evaluate synergistic use of SWRO brine and treated wastewater streams.
In Scenario 1, the baseline scenario, treated wastewater is blended with SWRO brine
prior to discharge (Figure 2-2a and detailed schematic in Figure A.1.1). The objective of this
scenario is to use treated wastewater to dilute the RO brine stream to maintain a discharge
salinity of 40 g/L. Because the treated wastewater is used only for brine dilution prior to disposal
and not for beneficial reuse purposes, this scenario does not make full use of the value of the
water resource embedded within the treated wastewater.
In Scenario 2 (Figure 2-2b and detailed schematic in Figure A.1.2), the RO brine stream
is used as a draw solution to extract high quality water from the treated wastewater under
isobaric conditions. The result is a diluted RO brine stream and a concentrated wastewater
stream as well as the capture of salinity gradient energy (Achilli and Childress, 2010; Han et al.,
(a)
(d) (c)
(b)

13
2013; She et al., 2012; Straub et al., 2014). In this study, salinity gradient energy capture was
modeled using pressure-retarded osmosis. In pressure-retarded osmosis, a semi-permeable
membrane separates the pressurized, high-salinity draw solution (i.e., the RO brine) from the
low-salinity feed solution (i.e., the treated wastewater). Through osmosis, water permeates from
the feed solution to the draw solution against the pressure gradient, diluting the RO brine (Achilli
et al., 2014; Prante et al., 2014). A portion of the chemical potential between the draw solution
and the low salinity feed solution is transformed into hydraulic pressure as water is transferred;
energy is recovered through depressurization (Plata and Childress, 2019). The concentrated
wastewater stream can then be blended with the diluted RO brine stream that is discharged to
the ocean or it can be sent back to the wastewater treatment facility.
In Scenario 3 (Figure 2-2c and detailed schematic in Figure A.1.3), treated wastewater is
blended with the intake seawater, creating a diluted feed stream for the RO process. This
scenario is considered direct potable reuse since treated wastewater is an influent to the RO
process that ultimately produces water for a potable supply (Linares et al., 2016). This scenario
is expected to be advantageous over Scenarios 1 and 2 because the volume of seawater
influent required is reduced. This reduction in seawater influent flowrate requirement has direct
implications for reduced infrastructure requirements for seawater intake systems. Additionally,
the energy requirements for RO decrease as the salinity of the feed solution decreases.
However, this scenario does require additional processes and monitoring to ensure that the
water quality of the RO permeate meets potable reuse regulations (National Water Research
Institute, 2018).
In Scenario 4 (Figure 2-2d and detailed schematic in Figure A.1.4), the intake seawater
is used as a draw solution to extract high-quality water from the treated wastewater using
osmotic dilution. In osmotic dilution, the driving force for transport across a forward osmosis
membrane is the osmotic pressure difference between the treated wastewater and the seawater
(Cath et al., 2006; Cath et al., 2010). As in Scenario 3, the diluted seawater becomes the

14
influent to the RO process and the concentrated wastewater stream can either be blended with
the brine stream that exits the RO process or it can be sent back to the wastewater treatment
facility. Although this process increases system capital and operating costs, the additional
treatment barrier that it provides may be necessary to achieve regulatory requirements for
pathogen removal. In addition, the forward osmosis process provides a low-energy, high-quality
pre-treatment process for the treated wastewater (Shaffer et al., 2012). In forward osmosis,
membrane fouling layers have been found to be more easily removed than in RO (Kim et al.,
2014; Lee et al., 2010; Xie et al., 2015). Thus, Scenario 4 is expected to require fewer additional
processes than Scenario 3 to ensure that the water quality of the RO permeate meets direct
potable reuse regulations.
2.2.3 Process models
Each process in the treatment train (e.g., pre-treatment, reverse osmosis, post-
treatment, and engineered osmosis) is modeled individually to determine flowrates and energy
consumption. The UF process was modeled using Dow Chemical Company’s DOW™ WAVE
Design Software - version 1.64 (Dow Chemical Company, 2019). The RO process was modeled
using both DOW™ WAVE Design Software and Power Model (Energy Recovery Inc, 2019)
because all scenarios incorporated an RO pressure exchanger to reduce energy consumption.
A PX Q300 pressure exchanger (Energy Recovery Inc., San Leandro, CA) was selected
because of its high efficiency. Forward osmosis and pressure-retarded osmosis were modeled
using the Engineered Osmosis Processes (EOP) solver (Binger and Achilli, 2020), which is a
module-scale solver that considers key aspects of spiral wound membrane modules and directly
estimates mass transfer and pressure losses in forward osmosis and pressure-retarded
osmosis. For both forward osmosis and pressure-retarded osmosis, a wastewater recovery of
90% was assumed.

15
2.2.3.1 Pre-treatment
In the four scenarios, UF was used as pre-treatment for SWRO, and also as pre-
treatment for the treated wastewater prior to RO, forward osmosis, and pressure-retarded
osmosis. A recovery of 90% was assumed for the UF process; 100% of the feed water was
converted to filtrate; however, 10% of the filtrate was used to backwash the UF membranes.
2.2.3.2 Reverse osmosis
In Scenarios 1 and 2 there is no dilution of the RO influent with treated wastewater so
the RO influent consists of 100% seawater. In Scenarios 3 and 4, when the RO influent is
diluted with treated wastewater, the RO influent consists of a blend of seawater and treated
wastewater (hereafter referred to as the SW:WW influent ratio). For example, a 40:60 SW:WW
influent ratio represents a blend of 40% seawater and 60% treated wastewater as the RO
influent.
The RO recovery (𝑅 𝑅𝑂
) for Scenarios 3 and 4 varies according to the SW:WW influent
ratio, and is calculated according to:
𝑹 𝑹𝑶
= 𝑺𝑾 % × 𝑹 𝑹𝑶 −𝒔𝒘
+ 𝑾𝑾 % × 𝑹 𝑹𝑶 −𝒘𝒘
(2.1)
where 𝑆𝑊 % is percentage of seawater in the RO influent; 𝑊𝑊 % is percentage of treated
wastewater in the RO influent; 𝑅 𝑅𝑂 −𝑠𝑤
is seawater RO recovery rate, which is assumed to be
50%; and 𝑅 𝑅𝑂 −𝑤𝑤
is treated wastewater RO recovery rate, which is assumed to be 80%. Based
on the RO recovery rate, the required RO influent flowrate (𝑭 𝑹𝑶 −𝒊𝒏𝒇𝒍𝒖𝒆𝒏𝒕 ) is:
𝑭 𝑹𝑶 −𝒊𝒏𝒇𝒍𝒖𝒆𝒏𝒕 =
𝑭 𝑷𝑾
𝑹 𝑹𝑶
(2.2)
where 𝐹 𝑃𝑊
is RO permeate flowrate. 𝐹 𝑃𝑊
is held constant at 1.14  10
4
m
3
/d for all scenarios. As
the SW:WW influent ratio decreases (i.e., as the percentage of treated wastewater increases),
the RO recovery rate increases according to Equation (2.1) and the RO influent flowrate
requirement decreases according to Equation (2.2). The RO influent flowrates of seawater and
treated wastewater required to achieve the product flowrate of 1.14  10
4
m
3
/d are shown in

16
Figure 2-3. A SW:WW influent ratio of 100:0 represents seawater desalination only (no
wastewater reclamation) and a SW:WW influent ratio of 0:100 represents wastewater
reclamation only (no seawater desalination).

Figure 2-3 RO influent flowrate requirements to achieve desired product water flowrate of 1.14 × 10
4
m
3
/d for
seawater:treated wastewater (SW:WW) influent ratios.
2.2.3.3 Second-pass RO for boron removal
In the current framework, the boron concentration limit is assumed to be 1 mg/L; second-
pass RO is deemed necessary when the boron concentration in the RO permeate exceeds this
value. DOW™ WAVE Design Software was used to calculate the energy consumption of full
second-pass RO and then a linear relationship between energy consumption difference and
influent boron concentration from Du et al. (2015) was used to estimate a value for only partial
second-pass RO.
2.2.3.4 Post-treatment
Advanced oxidation using UV light coupled with hydrogen peroxide (UV/H2O2) is an
industry-standard post-treatment process in potable reuse applications (National Water
Research Institute, 2018; Yin et al., 2018). UV/H2O2 degrades neutral-charged, low-molecular-
weight organics that pass through the RO membrane (Kimura et al., 2003; McCurry et al.,
2017). A UV dose of at least 300 mJ/cm
2
is necessary for 6-log removal of all known pathogens

17
(National Water Research Institute, 2018) and a UV dose of 900 mJ/cm
2
is used to destroy
disinfection by-products such as N-nitroso-dimethylamine (Gerrity et al., 2015). In the current
study, UV/H2O2 is modeled as a post-treatment process for the RO permeate in the influent
blending scenarios (Scenarios 3 and 4) with the dose varying between 300 and 900 mJ/cm
2

depending on the SW:WW influent ratio.
2.2.4 Estimation of energy consumption
For each scenario, specific energy consumption (SEC) and specific energy savings
(SES) were calculated for the individual processes. SEC values for RO (𝑺𝑬𝑪 𝑹𝑶
) and UF
(𝑺𝑬𝑪 𝑼𝑭
) were calculated using DOW™ WAVE Design Software and SEC values for forward
osmosis (𝑺𝑬𝑪 𝑭𝑶
) were calculated using EOP Solver. SEC values for UV/H2O2 (𝑺𝑬𝑪 𝑼𝑽 /𝑨𝑶𝑷 )
were estimated based on the literature (e.g., (Holloway et al., 2016; Tang et al., 2018)), which
shows that 𝑺𝑬𝑪 𝑼𝑽 /𝑨𝑶𝑷 has a linear relationship with the UV dose and ranges from 0.04 to 0.13
kWh/m
3
(detailed in Supplementary Information). SES values were calculated for the PX
(𝑺𝑬𝑺 𝑷𝑿
) by Power Model and for the pressure-retarded osmosis process (𝑺𝑬𝑺 𝑷𝑹𝑶 ) by EOP
Solver.
Net specific energy consumption (𝑺𝑬𝑪 𝑵𝒆𝒕 ) was calculated for each scenario using:
Scenario 1: 𝑺𝑬𝑪 𝑵𝒆𝒕 = 𝑺𝑬𝑪 𝑼𝑭
+ 𝑺𝑬𝑪 𝑹𝑶
− 𝑺𝑬𝑺 𝑷𝑿
(2.3)
Scenario 2: 𝑺𝑬𝑪 𝑵𝒆𝒕 = 𝑺𝑬𝑪 𝑼𝑭
+ 𝑺𝑬𝑪 𝑹𝑶
− 𝑺𝑬𝑺 𝑷𝑿
− 𝑺𝑬𝑺 𝑷𝑹𝑶 (2.4)
Scenario 3: 𝑺𝑬𝑪 𝑵𝒆𝒕 = 𝑺𝑬𝑪 𝑼𝑭
+ 𝑺𝑬𝑪 𝑹𝑶
+ 𝑺𝑬𝑪 𝑼𝑽 /𝑨𝑶𝑷 − 𝑺𝑬𝑺 𝑷𝑿
(2.5)
Scenario 4: 𝑺𝑬𝑪 𝑵𝒆𝒕 = 𝑺𝑬𝑪 𝑼𝑭
+ 𝑺𝑬𝑪 𝑹𝑶
+ 𝑺𝑬𝑪 𝑼𝑽 /𝑨𝑶𝑷 − 𝑺𝑬𝑺 𝑷𝑿
+ 𝑺𝑬𝑪 𝑭𝑶
(2.6)
All SEC and SES values are in units of kWh per cubic meter of product water (PW) (kWh/m
3
-
PW), where product water is RO permeate. The energy consumption of the UF process per
cubic meter of product water (𝑆𝐸𝐶 𝑈𝐹
) is calculated according to:
𝑆𝐸𝐶 𝑈𝐹
=
𝑆𝐸𝐶 𝑈𝐹 −𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒 ×𝐹 𝑈𝐹 −𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒 𝐹 𝑃𝑊
(2.7)

18
where 𝑆𝐸𝐶 𝑈𝐹 −𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒 is the energy consumption of the UF process per cubic meter of UF filtrate
and 𝐹 𝑈𝐹 −𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒 is UF filtrate flowrate.

2.3 Results and discussion
2.3.1 RO brine salinity
The RO brine salinity for each SW:WW influent ratio is shown in Figure 2-4. RO brine
salinity decreases as the SW:WW influent ratio decreases because the salinity of the treated
wastewater (0.6 g/L) is much less than that of seawater (35 g/L). The horizontal line in Figure 2-
4 indicates the limitation for discharge salinity (40 g/L) set in the current study. It can be seen
that to maintain a discharge salinity of 40 g/L without discharge dilution, the SW:WW influent
ratio must be 30:70 or less; at SW:WW influent ratios from 90:10 to 40:60, discharge dilution is
necessary alongside influent dilution.

Figure 2-4 RO brine salinity for seawater:treated wastewater (SW:WW) influent ratios. The horizontal line indicates
the limitation for discharge salinity (40 g/L) set in the current study. Operation at SW:WW influent ratios of 40:60 or
greater require discharge blending to meet the salinity limit; operation at SW:WW influent ratios of 30:70 or less does
not require discharge blending.
Limit of
discharge
salinity

19
2.3.2 Treated wastewater flowrates in hybrid systems
The data in Figure 2-5 shows treated wastewater flowrates required to meet the
limitation for discharge salinity. Because there is no influent dilution in Scenarios 1 and 2, these
scenarios are represented only by the 100:0 SW:WW influent ratio (Figure 2-5a). In Scenarios 1
and 2, to maintain a discharge salinity of 40 g/L, 8.19  10
3
m
3
/d of treated wastewater must be
blended with the RO brine.

Figure 2-5 Required treated wastewater flowrates for both influent dilution and discharge dilution for all
seawater:treated wastewater (SW:WW) influent ratios in (a) Scenarios 1 and 2 (the brine blending scenarios), (b)
Scenario 3 – the influent blending scenario, and (c) Scenario 4 – the influent blending scenario with osmotic dilution.
The horizontal line in Scenario 3 (Figure 2-5b) indicates the available amount of treated wastewater in the current
study.
In Scenario 3 (Figure 2-5b), there is no data point for SW:WW influent ratio 100:0
because the case of no influent dilution is already represented by Scenario 1. As the SW:WW
influent ratio decreases, the treated wastewater flowrate requirement increases. At SW:WW
influent ratios greater than 40:60, some treated wastewater is used for influent dilution and
some for discharge dilution. For example, when the SW:WW influent ratio is 50:50, even when
the seawater influent is diluted by 50% with treated wastewater, the RO brine still requires
dilution to achieve 40 g/L or less. According to Equation (2.1), the RO recovery rate is 65% (not
50%), thus the RO brine salinity prior to effluent dilution is 50 g/L (not 40 g/L) (Figure 2-4).
At influent ratios of 40:60 and less, discharge dilution is no longer needed to maintain a
discharge salinity of 40 g/L. This is important because when treated wastewater is used for
influent dilution, the value of the water resource is fully realized; when treated wastewater is
Available amount of
treated wastewater

20
used for discharge dilution, much of the value in the water resource is lost. At SW:WW influent
ratios of 10:90 and less, achieving the desired product water flowrate of 1.14  10
4
m
3
/d
requires more treated wastewater than is available, thus Scenario 3 is not feasible at SW:WW
influent ratios less than or equal to 10:90.
In Scenario 4 (Figure 2-5c), osmotic dilution is used to achieve influent dilution and pre-
treatment for the RO process. There are no data points for SW:WW influent ratios less than or
equal to 30:70 because the seawater flowrates for these ratios are too low to extract wastewater
through the forward osmosis process. Similar to Scenario 3 (Figure 2-5b), as the SW:WW
influent ratio decreases, the treated wastewater flowrate requirement increases.
Comparing the treated wastewater flowrate requirements for Scenarios 3 and 4 between
SW:WW influent ratios 90:10 and 60:40, the treated wastewater flowrates for Scenarios 3 and 4
are exactly the same even though the forward osmosis process has a recovery rate of 90%.
This is because all forward osmosis concentrate is used for discharge dilution. At the SW:WW
influent ratio of 50:50, Scenario 4 requires 5% more treated wastewater than Scenario 3
because only a portion of the forward osmosis concentrate is needed for discharge dilution (i.e.,
the forward osmosis concentrate flowrate exceeds the flowrate needed for discharge dilution).
At the SW:WW influent ratio of 40:60, Scenario 4 requires 10% more treated wastewater than
Scenario 3, because no treated wastewater is needed for discharge dilution.
If the goal is to operate a SWRO facility that meets a 40 g/L limitation for discharge
salinity and does not waste the water resource in the treated wastewater (i.e., all treated
wastewater is used for influent dilution) then Scenarios 3 and 4 would be operated at SW:WW
influent ratios of 40:60 and 50:50. At these blending ratios, no discharge dilution is needed.
Thus, SW:WW influent ratio of 40:60 in Scenario 3 and SW:WW influent ratio of 50:50 in
Scenario 4 were selected to represent Scenarios 3 and 4 in later discussion.

21
2.3.3 Discharge flowrates in hybrid systems
Discharge flowrates are depicted in Figure 2-6. The total discharge flowrates are similar
in magnitude for each SW:WW influent ratio, regardless of scenario, but the total discharge
flowrates decrease substantially with decreasing SW:WW influent ratio. In Scenarios 1 and 2,
the combined flowrates of UF retentate, treated wastewater, and pressure-retarded osmosis
concentrate (Scenario 2 only) are almost equal to the flowrate of RO brine. In Scenario 3, at
SW:WW influent ratios greater than 40:60, UF retentate alone is not enough to dilute the RO
brine to 40 g/L, thus, treated wastewater is also required. At SW:WW influent ratios less than or
equal to 40:60, UF retentate alone is enough to dilute the RO brine. In Scenario 4, forward
osmosis concentrate is also used for discharge dilution. Similar to Scenario 3, at SW:WW
influent ratios less than or equal to 50:50, UF retentate and forward osmosis concentrate are
enough to dilute the RO brine and no additional treated wastewater is required.

Figure 2-6 Discharge flowrates for seawater:treated wastewater (SW:WW) influent ratios in (a) Scenarios 1 and 2 (b)
Scenario 3, (c) Scenario 4.
In Scenarios 3 and 4, at lower SW:WW influent ratios where discharge dilution is not
necessary, the less UF retentate and less forward osmosis concentrate, the less wasted
discharge. Thus, at these conditions, higher UF and forward osmosis recovery rates are
preferred.
For Scenario 2 only – in
Scenario 1, this discharge is
additional treated wastewater

22
2.3.4 Boron concentration in RO permeate
The concentration of boron in the RO permeate for each SW:WW influent ratio is shown
in Figure 2-7. The horizontal line indicates the California State Notification Level of 1.0 mg/L for
boron. It can be seen that when the SW:WW influent ratio is greater than 60:40, additional
treatment is necessary to reduce the boron concentration to the regulatory limit. In the current
study, partial second-pass RO was modeled to reduce the boron concentration to 1.0 mg/L and
the resulting increase in energy consumption is discussed in the next section.

Figure 2-7 Boron concentration in RO permeate for seawater:treated wastewater (SW:WW) influent ratios.
2.3.5 Specific energy consumption and specific energy savings in hybrid systems
2.3.5.1 Specific energy consumption of RO
The RO SEC values for each SW:WW influent ratio are shown in Figure 2-8. For influent
ratios of 60:40 and less, second-pass RO is not required to maintain boron reduction less than
1.0 g/L. For influent ratios of 70:30 or greater, when partial second-pass RO (Pass 2) is
required, the RO SEC increases by 34% specifically due to the second pass.
California State
Notification Level

23

Figure 2-8 RO specific energy consumption for seawater:treated wastewater (SW:WW) influent ratios.
2.3.5.2 Energy consumption of pre-treatment and post-treatment
UF is used for pre-treating seawater in all scenarios and for pre-treating treated
wastewater in Scenarios 3 and 4. The UF SEC decreases as the SW:WW influent ratio
decreases from 100:0 to 0:100 (Figure A.1.5 in Supplementary Information). This decrease is
not because the UF SEC for pre-treatment of seawater is higher than that of treated
wastewater; in fact, they are the same (both are 0.07 kWh/m
3
). Instead, total UF SEC decreases
because a higher RO recovery rate can be used when the seawater is diluted with treated
wastewater (Figure 2-3) so the influent flowrate to UF is less.
UV/H2O2 is modeled as a post-treatment process for the RO permeate in Scenarios 3
and 4. The UV dose increases linearly from 300 to 900 mJ/cm
2
with decreasing SW:WW influent
ratio (Table A.1.1 in Supplementary Information). In Scenario 3, the UV SEC increases from
0.04 to 0.13 kWh/m
3
. Pertaining to Scenario 4, it has been demonstrated in previous studies
that forward osmosis rejection is greater than 40% for tested organic compounds in bench-scale
experiments and greater than 60% for tested organic compounds in pilot-scale experiments
(Hancock et al., 2011). Based on this, rejection of organic compounds by forward osmosis in
this study is assumed to be 50%. Thus, with the additional barrier provided by osmotic dilution in

24
Scenario 4, the UV dose is set to range from 300 to 450 mJ/cm
2
only (Table A.1.1 in
Supplementary Information); over this range, the UV SEC increases from 0.04 to 0.06 kWh/m
3
.
2.3.5.3 Integration into system-scale model
Net SEC values calculated from Equations (2.3)-(2.6) are shown in Figure 2-9. In
Scenario 1 (the baseline Scenario), the net SEC is 3.5 kWh/m
3
. This overall energy
consumption is approximately two times the theoretical minimum energy of RO (1.8 kWh/m
3

(Elimelech and Phillip, 2011)) due to the need for partial second-pass RO, UF, and UV/H2O2
processes. In Scenario 2, the net SEC is 0.42 kWh/m
3
less than that in Scenario 1 due to
energy recovery by pressure-retarded osmosis. Based on the available flowrates and
concentrations of the RO brine and treated wastewater streams, 0.599 kWh/m
3
of specific
energy is theoretically available for the pressure-retarded osmosis system to recover (Yip and
Elimelech, 2012). The difference between the theoretical thermodynamic potential and the
modeled result (30%, or 0.18 kWh/m
3
) is due to unutilized energy and friction losses (O'Toole et
al., 2016). In Scenario 3, as the SW:WW influent ratio decreases from 90:10 to 0:100, the net
SEC decreases from 3.4 to 0.6 kWh/m
3
. In Scenario 4, the net SEC values are a little higher
than those in Scenario 3 because of the higher UV doses required in Scenario 3. All in all,
decreasing the percentage of seawater has a much greater effect on decreasing net SEC than
the choice of scenario.

25
Figure 2-9 Net SEC comparison for seawater:treated wastewater (SW:WW) influent ratios in four scenarios.
2.3.5.4 Composition of net SEC
The data in Figure 2-10 shows the SEC percentages for each process. In Scenario 1
(Figure 2-10a), the SEC percentage of RO and UF are 95.9, and 4.1%. In Scenario 2, the SEC
percentage of RO decreases to 93.9% because the pressure-retarded osmosis sub-system
reduces the overall SEC by recovering salinity gradient energy from blending the RO brine with
the treated wastewater. In addition, in Scenario 2, the SEC percentage of UF increases to 6.1%
because Scenario 2 replaces the direct blending in Scenario 1 with a pressure-retarded osmosis
process, which requires UF as pre-treatment. In Scenario 3, as the SW:WW influent ratio
decreases from 90:10 to 0:100, the SEC percentage of RO decreases and the SEC
percentages of UF and UV/H2O2 increase. With increasing treated wastewater, RO SEC
decreases, the UV/H2O2 SEC increases slightly, and UF SEC decreases slightly. In Scenario 4,
the SEC percentage of UF is slightly higher than Scenario 3 because Scenario 4 replaces the
direct blending in Scenario 3 with forward osmosis that is operated at 90% recovery. Thus,
compared to Scenario 3, more treated wastewater needs to be pre-treated by UF prior to
forward osmosis in Scenario 4. The SEC percentage of UV/H2O2 in Scenario 4 is 29% lower
than that of Scenario 3 on average, because the additional barrier provided by osmotic dilution
reduces the UV dose requirement. Also, considering that the additional wastewater biofoulants
in the RO influent are being rejected at higher pressure than are typically used in RO for
wastewater reuse, the high-quality pre-treatment offered by forward osmosis in Scenario 4 may
be valuable. In addition, forward osmosis only contributes negligibly (less than 0.5%) to the
SEC.

26

Figure 2-10 Percentage of RO, UF, UV/ H2O2, and forward osmosis (FO) in net SEC for seawater:treated wastewater
(SW:WW) influent ratios in (a) Scenario 1, (b) Scenario 2, (c) Scenario 3, and (d) Scenario 4.
2.3.5.5 Specific energy comparison for select conditions of four scenarios
Energy consumptions in all scenarios are depicted in Figure 2-11. SEC values for all
processes are shown above the x-axis and SES values are shown below the x-axis. Also shown
for each scenario is the net SEC (the sum of SEC values minus the sum of SES values). As
mentioned in Section 3.2, for Scenarios 3 and 4, 40:60 and 50:50 are selected to compare with
Scenarios 1 and 2 because they represent conditions that meet the limitation for discharge
salinity but do not waste the water resources in the treated wastewater (i.e., all treated
wastewater is used for influent dilution). In Scenarios 1 and 2, the RO SEC is greater than in
Scenarios 3 and 4 because with no influent dilution, the RO operates at higher pressure in first-
pass RO and also, second-pass RO is required for boron control. In Scenario 4, forward

27
osmosis provides a highly selective pre-treatment with only 11% increase in SEC when
compared to Scenario 3.

Figure 2-11 RO, UF, UV/H2O2, and forward osmosis (FO) specific energy consumptions, and pressure-retarded
osmosis (PRO) and ERD specific energy savings for Scenarios 1-4. The net SEC is calculated by subtracting total
SES from total SEC.
2.3.6 Summary for select conditions of four scenarios
The data in Figure 2-12 shows the seawater intake flowrates, treated wastewater
flowrates, discharge flowrates, and SECs for the selected SW:WW influent ratio conditions. It is
important to note that the product water flowrate is constant across all scenarios. Compared to
Scenarios 1 and 2 (without influent dilution), seawater influent flowrates, discharge flowrates,
and net SECs in Scenarios 3 and 4 are approximately 66, 63 and 42% lower. The reason is that
when treated wastewater is used for influent dilution, rather than discharge dilution, a larger
fraction of treated wastewater can be recovered as product water. In addition, the treated
wastewater flowrates in Scenarios 3 and 4 are 34% higher than that of Scenarios 1 and 2 (but
not as much as double) mainly because the reduced influent salinity of RO in Scenarios 3 and 4

28
allows higher RO recovery rate. In Scenario 2, the pressure-retarded osmosis subsystem
reduces energy consumption without requiring additional treated wastewater.

Figure 2-12 RO, UF, UV/H2O2, and forward osmosis (FO) specific energy consumptions, and pressure-retarded
osmosis (PRO) and ERD specific energy savings for Scenarios 1-4.

2.4 Conclusion and implication
Given the multiple benefits of the influent blending scenarios (Scenarios 3 and 4),
including that: 1) seawater intake and discharge requirements are reduced, 2) second-pass RO
for boron control is no longer required, 3) energy consumption is reduced, 4) seawater and
treated wastewater constituents in the brine to be disposed are diluted 5) land footprint is saved,
and 6) pumping volumes are saved, the advantage of these scenarios is clear. Even though
salinity gradient energy recovered in Scenario 2 decreases the overall energy consumption, the
saving is not as significant as the RO energy savings that occur at lower seawater percentages
in the influent blending scenarios (Scenarios 3 and 4). Beyond the framework, technical and
societal challenges associated with direct potable reuse must be considered. With consideration
of developing regulatory requirements for potable reuse (National Water Research Institute,

29
2018), the benefits of osmotic dilution over other advanced processes must be considered. If
real-time membrane failure detection comes to fruition for forward osmosis (Desormeaux 2017),
the ability to achieve additional log removal value credits would provide significant value.
Although the framework was developed for use with co-located seawater desalination
and coastal wastewater reclamation facilities, its use can be extended for to co-located, or close
proximity, desalination and wastewater reclamation facilities in in-land locations. At these
facilities, disposal of RO concentrate is perhaps a more serious concern. Considering the large
number of seawater and brackish water RO facilities that are in planning, construction, and
operation in the west and other arid regions of the world, the developed framework could have a
broad reach.

Acknowledgement
This work was supported by the Electric Power Research Institute (10007871), the
University of Southern California’s Theodore and Wen-Hui Chen Endowed Fellowship, the
University of Southern California’s Viterbi School of Engineering Fellowship.

30
3 CHAPTER 3. Potable Reuse of Reclaimed Wastewater with
Increasing Salinity: Water Recovery and Energy
Consumption

This chapter is under revision in Environmental Science & Technology as of May 2021
Abstract
With reverse osmosis (RO) membranes being industry-standard in many potable reuse
facilities, an opportunity exists to desalinate higher-salinity streams (e.g., brine or concentrate
“waste” streams) to augment traditional water and wastewater supplies and address brine
management issue in inland desalination. This analysis was done considering with or without
seawater inflow and intrusion, which raises the salinity of wastewater. This study evaluates the
energy consumed in recovering water from these streams at advanced water purification
facilities. The benefits provided by the pretreated brine streams are weighed against the
additional energy consumption. It was found that the rate of energy consumption change of
desalinating high-salinity streams decreases as wastewater salinity increases and that rate of
energy consumption change is expected to have a decreasing trend in future years. Multiple
energy saving strategies are evaluated, including energy recovery device (ERD), closed-circuit
RO (CCRO), and desalinating higher-salinity streams separately from treated wastewater. The
energy savings from ERD and CCRO increase with influent salinity increase. However, the
energy savings from desalinating higher-salinity streams separately increases with increasing
difference of two streams’ salinities. Addition of higher-salinity streams must also be considered
within the context of enhanced source control, discharge permits, and capital and operating
costs.

31
3.1 Introduction
Potable reuse, or the process of converting wastewater into water that can be reused for
potable purposes, is a well-established practice to provide a local, drought-proof water supply in
water-scarce regions (Tchobanoglous et al., 2015; US Environmental Protection (US EPA),
2020). Conversion of wastewater to potable water may begin at a wastewater treatment or
reclamation facility and continue at an advanced water purification facility (AWPF); alternatively,
a wastewater reclamation facility may be retrofitted with advanced water treatment processes if
space is available.
According to a 2015 Bluefield report, the US leads the world in potable reuse projects
(Bluefield Research, 2015; Meridian Institute and Paradigm Environmental, 2018). Orange
County Water District’s (OCWD’s) Groundwater Replenishment System, which is currently
undergoing expansion from 100 to 130 million gallons/day (MGD) production capacity, is the
world’s largest AWPF for indirect potable reuse via groundwater recharge. According to the
2017 Potable Reuse Compendium (US Environmental Protection (US EPA), 2018), potable
reuse installations are expected to increase in the US and internationally. For example,
Singapore operates five NEWater facilities that reclaim wastewater mostly for high-quality
industrial use but also for indirect potable reuse via reservoir augmentation. The NEWater
facilities are expected to meet up to 55% of Singapore’s water demand by 2060 (Singapore
National Water Agency, 2021b).
As the volume of wastewater being reclaimed for potable reuse has significantly
increased in the past 10-20 years, reverse osmosis (RO) installations have proliferated
(Hamoda et al., 2015; Kurihara and Hanakawa, 2013; Lyu et al., 2016; Tang et al., 2016; Tang
et al., 2014; Wenten and Khoiruddin, 2016). In California, potable reuse regulations require RO
processes at AWPFs when the product water is being directly injected into the groundwater or
being used for reservoir augmentation (California State Water Resources Control Board, 2018).

The RO process separates contaminants such as pathogens, disinfection byproducts (DBPs),

32
and trace organic compounds (Alturki et al., 2010; Lively and Sholl, 2017; Wintgens et al., 2005;
Zeng et al., 2016)

as well as dissolved solids/salinity.
3.1.1 Role of desalination in water reuse
Over the last decades, salinity levels in wastewater have increased, in large part due to
residential water treatment systems (e.g., water softeners and septic systems) (Venkatesan et
al., 2011), industrial uses (Sardari et al., 2018), water conservation measures (Schwabe et al.,
2020), operation of desalination systems at upstream facilities, and also, in coastal regions,
seawater inflow and infiltration (I&I) (King County Department of Natural Resources and Parks,
2011). At coastal wastewater reclamation facilities located at low elevation, leaky gates,
corroded pipes, and aging infrastructure may allow seawater to pass through sewage
conveyance pipes and connections and intrude into wastewater reclamation facilities (Krayer et
al., 2017). As treatment-plant influents have become more saline, desalination by RO in AWPFs
has regained importance. Hence, while the role of RO membranes in separating pathogens and
trace organic compounds is still key, the role of RO membranes in separating salts for potable
reuse applications is being rediscovered as critical.
With RO membranes being industry-standard at most AWPFs (Gerrity et al., 2013;
Warsinger et al., 2018), an opportunity exists to desalinate higher-salinity streams (e.g., brine
“waste” streams), to augment traditional wastewater supplies. If higher-salinity streams are
discharged to a wastewater reclamation facility that supplies an AWPF, the salinity from these
streams is conserved through the wastewater treatment processes and would then be
separated by the RO process at the AWPF. Desalination of the higher-salinity stream along with
treated wastewater would increase the supply of water available for potable reuse while at the
same time, reduce the volume of discharge, which may be useful depending on the ultimate
discharge goal. Recovering water from the higher-salinity stream imparts value to this impaired
water source that is otherwise considered a waste stream.

33
3.1.2 Higher-salinity streams examples
In this paper, “higher-salinity streams” refers to brackish water RO (BWRO) brine
streams and regional brine interceptor/collector streams that have salinities greater than 2 g/L
(i.e., greater than the salinity of typical wastewater) (Al-Obaidi et al., 2020; Lazarova et al.,
2003). BWRO facilities for inland groundwater desalination typically produce brines with
salinities greater than 10 g/L and TOC concentrations less than 15 mg/L (Fard et al., 2016; Ji et
al., 2010; Lee et al., 2016; Pramanik et al., 2017). The cost of brine disposal ranges from 5 to
33% of the total cost of desalination (Panagopoulos et al., 2019). Also, brine discharge
regulations often limit the capacity of BWRO facilities (Walker, 2010). Some BWRO facilities
discharge their brine to a regional brine interceptor that conveys the brine to a wastewater
reclamation facility, where it is treated prior to ocean discharge (Voutchkov, 2018a). A well-
known example of a regional brine interceptor is the Inland Empire Brine Line in Southern
California, USA. The Inland Empire Brine Line conveys combined flows of brines from desalters,
concentrated waste streams, and effluent from the treatment facility of a hazardous waste site.
With a capacity of 30 MGD, the Inland Empire Brine Line currently has an average flowrate of
12 MGD, an average salinity (in 2020) of 5.7 g/L (Santa Ana Watershed Project Authority
(SAWPA), 2021), and a TOC concentration of approximately 7 mg/L (Santa Ana Watershed
Project Authority (SAWPA), 2021; Voutchkov, 2018a). The Inland Empire Brine Line becomes
the Santa Ana Regional Interceptor, which includes local wastewater collected along the
pipeline alignment in Orange County. Due to higher salinity levels and irregular discharges that
may occur in the Inland Empire Brine Line, the Santa Ana Regional Interceptor flow is treated as
a separate flow by the Orange County Sanitation District. Unlike wastewater in the trunk sewer
line, the treated Santa Ana Regional Interceptor flow is discharged to the ocean and is not used
as source water for potable reuse through the Groundwater Replenishment System (Scott-
Roberts, 2016).

34
3.1.3 Energy and water recovery by energy recovery devices and high-recovery RO
Two-stage RO, where the concentrate from the first stage becomes the feed to the
second stage (Figure 3-1a), is often used in AWPF RO and BWRO processes to increase water
recovery (Kim et al., 2020). Two-stage RO reduces the specific energy consumption (𝑆𝐸𝐶 ) of
the desalination process by decreasing the irreversible work (i.e., the energy lost) in the RO
process (Park et al., 2020).

Figure 3-1 Diagrams for (a) two-stage RO, (b) two-stage RO with an energy recovery device, and (c) closed-circuit
RO.
High energy costs in the water sector have led many water and wastewater treatment
facilities to include energy management strategies as part of their daily operation (Zohrabian et
al., 2021). For example, energy recovery devices (ERDs) (Figure 3-1b) are commonly used in
conjunction with high-salinity RO processes (e.g., seawater RO) to provide specific energy
savings (𝑆𝐸𝑆 ) and reduce the 𝑆𝐸𝐶 of the desalination process (Jeon et al., 2017; Li, 2012; Liu et
al., 2016). ERDs reduce energy consumption by transferring the energy left in the RO
concentrate back to the feed stream via centrifugal or positive displacement isobaric devices
(e.g., pressure exchangers and turbochargers) (Kadaj and Bosleman, 2018). ERDs can reduce
the energy consumption at seawater RO desalination facilities by as much as 67%, depending
on operating conditions. In BWRO facilities and AWPFs, the low feed water salinity and
relatively low brine flowrate make the benefits of ERDs ambiguous (Drak and Adato, 2014).
Although ERDs are not commonly used in AWPFs (see Table A.2.1), if higher-salinity streams
are considered for augmenting influent, use of an ERD may become beneficial.

35
High-recovery RO processes (e.g., closed-circuit reverse osmosis (CCRO)) are being
considered at AWPFs to improve water recovery while keeping energy consumption low
(Warsinger et al., 2016). CCRO is a semi-batch process in which the brine is recirculated while
water permeates through the RO membrane (Figure 3-1c). Pressurized feed water is
continuously added to the brine, which is not depressurized, and the mixture is returned to the
membrane module to be separated. Once the desired water recovery is reached, the brine
stream is ejected and replaced by new feed solution (Warsinger et al., 2016). For lower-salinity
and lower-brine-flowrate applications, such as in AWPF RO and BWRO processes, CCRO may
provide greater water and energy benefits than ERDs (Warsinger et al., 2016). Model results
from Warsinger et al. (Warsinger et al., 2016). predict that CCRO can have up to 37% less
energy requirements than a standard BWRO process operating at high water-recovery. Other
than achieving high water-recovery with reduced energy consumption, CCRO may offer better
resistance to fouling and scaling and operate at higher average fluxes due to higher crossflow
velocities (Stover, 2013; 2016).
3.1.4 Previous work and objectives
In our previous study (i.e., Wei et al. (Wei et al., 2020)), a modeling framework was
developed to evaluate synergistic blending of treated wastewater with seawater RO process
streams. It was found that potable reuse blending scenarios, where treated wastewater is
blended with intake seawater had multiple benefits including reduced energy consumption,
reduced seawater intake volume requirements, and reduced discharge volumes compared to
scenarios with seawater only as the influent.
In the current research, we consider an inverse scenario: blending higher-salinity
streams with wastewater upstream of RO desalination at an AWPF. The higher-salinity streams
under consideration include RO brine streams and regional brine interceptor streams in
scenarios without and with seawater I&I, where scenarios with seawater I&I include additional
salinity from I&I processes that are common in coastal regions. In all cases, the higher-salinity

36
streams can provide an additional treatment-plant influent that has likely undergone filtration
(either in the subsurface or at a BWRO facility) and may have lower levels of organic matter and
other foulant material than the wastewater they will be blended with. The objective of the current
study is to evaluate the additional energy consumed in recovering water from higher-salinity
streams blended into AWPF influent and to weight the benefits of increasing the supply of
reclaimed water (by providing additional treatment-plant influent) against the additional energy
consumption due to the increased salinity of the influent. Opportunities to implement or enhance
energy and water recovery using an ERD and high-recovery RO are considered. Recognizing
that blending streams with different salinities generates entropy and raises the thermodynamic
least work to recover the water, an option of desalinating the higher-salinity streams separately
is also considered. This paper also considers inorganic scaling that can result from desalinating
AWPF influent influenced by seawater I&I and higher-salinity streams as well as whether
permeate and brine salinities will meet regulatory requirements on product and discharge
streams.

3.2 Methodology
3.2.1 Flowrates and salinities of treated wastewater, intruded seawater, and higher-salinity
streams
All simulations were based on a large AWPF with 134 MGD (5.1×10
5
m
3
/day) of
secondary-treated wastewater entering the AWPF. 40 MGD (1.5×10
5
m
3
/day) of higher-salinity
streams were added to mimic the additional influent flowrate required for the OCWD
Groundwater Replenishment System to achieve its final expansion capacity. An industry-
standard AWPF treatment train with UF, RO, and UV/H2O2 processes was modeled for treating
the secondary-treated wastewater effluent. Example salinities of secondary-treated wastewater
effluents serving as influent to selected AWPFs are listed in Table A.2.2.

37
For the scenario without seawater I&I, 1.2 g/L was used as the secondary-treated
wastewater effluent (AWPF influent) salinity. For the seawater I&I scenarios, 2.5, 5, 7.5, and
10% were considered, where the 2.5% seawater I&I scenario assumed a volumetric blending of
2.5% seawater with 97.5% secondary-treated wastewater effluent. Assuming the intruded
seawater has a salinity close to that of bulk seawater (Stein et al., 2016), the world-average
salinity of seawater (34.4 g/L (Ocean Health, 2020)) was used as the salinity of intruded
seawater. Calculated salinities for the 2.5, 5.0, 7.5, and 10% seawater I&I scenarios were 2.0,
2.8, 3.6, and 4.4 g/L.
Typical salinities of BWRO brines and a regional brine interceptor were used in the
simulations. For the BWRO brines, because the salinity of source waters to BWRO facilities can
range from 0.5 to 10 g/L with very different ionic compositions (Voutchkov, 2018b) and because
the water recoveries of BWRO facilities also range broadly (Alghoul et al., 2009; Altaee and
Hilal, 2015), three example salinities were selected: 7.5 (Martinetti et al., 2009), 10.9 (Oren et
al., 2010), and 17.5 g/L (Martinetti et al., 2009). The regional brine interceptor stream was
modeled after a portion of the Inland Empire Brine Line. Although the Inland Empire Brine Line
includes industrial wastewater contributions, for the purposes of this research, a brine
interceptor that comprises only brines from desalters and ion exchange facilities was modeled; a
salinity of 5.7 g/L (Santa Ana Watershed Project Authority (SAWPA), 2021) was used.
A schematic showing flowrates and salinities of the wastewater, intruded seawater, and
higher-salinity streams is shown in Figure 3-2. The higher-salinity streams can be blended with
the wastewater at two possible locations; depending on their water quality, the higher-salinity
streams can be blended 1) into the wastewater reclamation facility influent or 2) into the AWPF
influent (bypassing the wastewater reclamation facility). The second combination point has the
benefit of avoiding salinity increases in the biological process at the wastewater reclamation
facility. Salinities of the AWPF influent (i.e., the b values in Figure 3-2) are the salinity of the

38
blended wastewater, intruded seawater, and higher-salinity stream that are summarized in
Table 3-1.

Figure 3-2 Schematic of flowrates and salinities for the wastewater, intruded seawater, and higher-salinity streams
entering an advanced water purification facility. X represents the percentage of seawater I&I; a represents the salinity
of the higher-salinity stream; b represents the influent salinity to the advanced water purification facility (see Table 3-
1); c and d represent the resulting salinities of the RO permeate and brine streams. There are two possible blending
points for the higher-salinity streams (points 1 and 2), selection of which depends on the water quality of the higher-
salinity stream. Because wastewater treatment processes generally do not decrease salinity, the choice of blending
point does not affect salinity values b, c, and d.
Table 3-1 Salinities of the advanced water purification facility influent for all scenarios considered. The 25 values
shown in the table are used as the b value in Figure 3-2.

Seawater
I&I
(%)
Influent salinity
without higher-
salinity streams
(g/L)
Influent salinity
with
brine interceptor (g/L)
Influent salinity
with BWRO
brine 1 (g/L)
Influent salinity
with BWRO
brine 2 (g/L)
Influent
salinity with
BWRO brine 3
(g/L)
0 1.2 2.2 2.6 3.4 4.9
2.5 2.0 2.9 3.3 4.1 5.6
5 2.8 3.5 3.9 4.7 6.2
7.5 3.6 4.1 4.5 5.3 6.8
10 4.4 4.7 5.1 5.9 7.4

3.2.2 Modeling framework
A framework, similar to that developed in our previous study (i.e., Wei et al. (Wei et al.,
2020)) was used. The SEC of the RO process was determined using DOW
TM
WAVE design
software (DuPont Water Solution, 2020). The RO membrane module used in the simulations
was the BW30XFRLE-400/34i module (DuPont Water Solutions, Edina, MN), which is suitable
for both potable water reuse and industrial water demineralization. The RO water-recovery was
set to 85% based on target system recoveries for large-scale AWPFs (Bartels et al., 2005;

39
DUPONT, 2021; Scott-Roberts, 2016). The RO system was simulated with 26 trains, with each
train having a two-stage RO array. In stages 1 and 2, there were 88 and 34 vessels, with each
vessel containing seven membrane elements.
Simulations of the ultrafiltration (UF) pretreatment process and UV/H2O2 advanced
oxidation process were adapted from our previous study (i.e., Wei et al. (Wei et al., 2020)).
Given that the seawater I&I and higher-salinity brine streams have likely undergone filtration
(either in the subsurface or at a BWRO facility), it is assumed that blending the higher-salinity
streams into the UF feed will not significantly affect the energy required by the UF or UV/H2O2
processes. The UF process was simulated with 90% water recovery using WAVE design
software; the 𝑆𝐸𝐶 per cubic meter of UF filtrate (𝑆𝐸𝐶 𝑈𝐹 −𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒 ) was determined to be 0.09
kWh/m
3
. The 𝑆𝐸𝐶 of the UF process per cubic meter of product water (𝑆𝐸𝐶 𝑈𝐹
) was determined
to be 0.11 kWh/m
3
. A UV dose of 900 mJ/cm
2
was simulated for treating the RO permeate. At
this dose, the 𝑆𝐸𝐶 of the UV/H2O2 process per cubic meter of product water (𝑆𝐸𝐶 𝑈𝑉 /𝐻 2
𝑂 2
) is 0.13
kWh/m
3
(Wei et al., 2020).
𝑆𝐸𝐶 values for UF, RO, and UV/H2O2 are summed as 𝑆𝐸𝐶 𝑁𝑒𝑡 . For scenarios not using an
ERD 𝑆𝐸𝐶 𝑁𝑒𝑡 is calculated as:
𝑆𝐸𝐶 𝑁𝑒𝑡 = 𝑆𝐸𝐶 𝑈𝐹
+ 𝑆𝐸𝐶 𝑅𝑂
+ 𝑆𝐸𝐶 𝑈𝑉 /𝐻 2
𝑂 2
(3.1)
In simulations where an ERD is implemented, the specific energy saving (𝑆𝐸𝑆 ) was determined
using:
𝑆𝐸𝑆 =
𝑃 𝑏𝑟𝑖𝑛𝑒 ×𝐹 𝑏𝑟 𝑖𝑛𝑒
𝐹 𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 (3.2)
where 𝑃 𝑏𝑟𝑖𝑛𝑒 is hydraulic pressure of the RO brine, 𝐹 𝑏𝑟𝑖𝑛𝑒 is flowrate of the RO brine, and
𝐹 𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 is RO permeate flowrate. 𝑆𝐸𝐶 𝑁𝑒𝑡 for these simulations was calculated as:
𝑆𝐸𝐶 𝑁𝑒𝑡 = 𝑆𝐸𝐶 𝑈𝐹
+ 𝑆𝐸𝐶 𝑅𝑂
+ 𝑆𝐸𝐶 𝑈𝑉 /𝐻 2
𝑂 2
− 𝑆𝐸𝑆 (3.3)
All 𝑆𝐸𝐶 and 𝑆𝐸𝑆 values are in units of kWh per cubic meter of product water.

40
The CCRO process was modeled using DOW
TM
WAVE design software (DuPont Water
Solution, 2020). The high-recovery RO process was simulated using the FilmTec
TM
SOAR-4000
membrane module (DuPont Water Solutions, Edina, MN) with water-recovery set at 85% for
comparison with two-staged RO. The high-recovery RO system was simulated with 26 trains,
each having a one-stage RO array and 122 vessels, with each vessel containing seven
membrane elements. 𝑆𝐸𝐶 𝑁𝑒𝑡 for high-recovery RO was calculated using Equation (3.1).
If the higher-salinity streams are desalinated in a separate RO train and not in the AWPF
RO train, operation of the two RO processes at different water recoveries may be desired. In
order to achieve an overall 85% recovery (and provide the additional water supply of 40 MGD),
the relationship between the two water recoveries can be formulated as:
𝑊𝑅
𝑤𝑤
× 134 𝑀𝐺𝐷 + 𝑊𝑅
ℎ𝑠𝑠
× 40 𝑀𝐺𝐷 = 85% × 174 𝑀𝐺𝐷 (3.4)
where 𝑊𝑅
𝑤𝑤
is RO water recovery for the treated wastewater, and 𝑊𝑅
ℎ𝑠𝑠
is RO water recovery
for the higher-salinity stream. WAVE design software was then used to separately determine
𝑆𝐸𝐶 𝑁𝑒𝑡 for the treated wastewater (𝑆𝐸𝐶 𝑁𝑒𝑡 _𝑤𝑤
) and 𝑆𝐸𝐶 𝑁𝑒𝑡 for the higher-salinity stream
(𝑆𝐸𝐶 𝑁𝑒𝑡 _ℎ𝑠𝑠
). The combined 𝑆𝐸𝐶 𝑁𝑒𝑡 was then calculated using:
𝑆𝐸𝐶 𝑁𝑒𝑡 =
𝑆𝐸𝐶 𝑁𝑒𝑡 _𝑤𝑤
×𝑊𝑅
𝑤𝑤
×134 𝑀𝐺𝐷 +𝑆𝐸𝐶 𝑁𝑒𝑡 _ℎ𝑠𝑠
×𝑊𝑅
ℎ𝑠𝑠
×40 𝑀𝐺𝐷 85%×174 𝑀𝐺𝐷 (3.5)
3.2.3 Inorganic scaling potential considering seawater I&I and higher-salinity streams
Considering seawater I&I and the blending of higher-salinity streams into the treated
wastewater, inorganic fouling was considered using the Langelier Saturation Index (LSI). LSI is
used to predict the precipitation of calcium carbonate during RO desalination (Langelier, 1936).
LSI was selected because calcium carbonate is a frequently encountered scale on BWRO
membranes (Lee et al., 2020; Mitrouli et al., 2013; Yang et al., 2008) and because LSI is
appropriate for influent salinities less than 10 g/L. An LSI result less than zero means there is
little scaling potential and as LSI increases, scaling potential also increases (Antony et al.,

41
2011). LSI is compared for the cases when higher-salinity streams are blended with the treated
wastewater versus when the higher-salinity streams are desalinated separately.

3.3 Results and discussion
3.3.1 Effect of seawater I&I and higher-salinity streams on 𝑆𝐸𝐶 𝑁𝑒𝑡
Values of 𝑆𝐸𝐶 𝑁𝑒𝑡 without and with higher-salinity streams were calculated and the results
are shown in Figure 3-3. The conditions without higher-salinity streams, given by the first bar of
each group and the red horizontal line, represent the base cases for the five seawater I&I
scenarios. At 0% seawater I&I, the base case 𝑆𝐸𝐶 𝑁𝑒𝑡 is 0.54 kWh/m
3
(the first bar of the first
group). As the higher-salinity streams are considered (the next four bars of the first group),
𝑆𝐸𝐶 𝑁𝑒𝑡 increases with increasing stream salinity. Comparing base case 𝑆𝐸𝐶 𝑁𝑒𝑡 values for the
five scenarios, it can be seen that 𝑆𝐸𝐶 𝑁𝑒𝑡 increases from 0.54 to 0.95 kWh/m
3
as seawater I&I
increase from 0 to 10%. This range is consistent with previous research on energy consumption
in RO-based water reuse (e.g., 0.76 kWh/m
3
from Holloway et al. (2016)). As base case 𝑆𝐸𝐶 𝑁𝑒𝑡
increases with increasing seawater I&I, the percent increase of 𝑆𝐸𝐶 𝑁𝑒𝑡 caused by mixing higher-
salinity streams decreases. In other words, for the 10% seawater I&I base case (the first bar of
the last group), 𝑆𝐸𝐶 𝑁𝑒𝑡 is 0.95 kWh/m
3
and when BWRO brine 3 is added (the last bar of the last
group), 𝑆𝐸𝐶 𝑁𝑒𝑡 is 1.33 kWh/m
3
. This is only a 40% increase compared to the 81% increase in
𝑆 𝐸 𝐶 𝑁𝑒𝑡 for the 0% seawater I&I case. Thus, it can be seen that the rate of 𝑆𝐸𝐶 𝑁𝑒𝑡 change
caused by higher-salinity streams (Δ𝑆𝐸𝐶 𝑁𝑒𝑡 /Δ𝑠𝑎𝑙𝑖𝑛𝑖𝑡𝑦 ) decreases as seawater I&I increases
(Figure A.2.1). Looking to the future, base case salinity is expected to continue increasing
(Befus et al., 2020; Hummel et al., 2018) and as it does, the reduced rate of 𝑆𝐸𝐶 𝑁𝑒𝑡 change will
bring greater value to utilizing the water resource in higher-salinity streams.

42

Figure 3-3 𝑆𝐸𝐶 𝑁𝑒𝑡 without and with higher-salinity streams for the five seawater I&I scenarios. The first bar in each
group represents the 𝑆𝐸𝐶 𝑁𝑒𝑡 for advanced water purification facilities without adding higher-salinity streams (the base
case). The other four bars in each group represent the 𝑆𝐸𝐶 𝑁𝑒𝑡 for advanced water purification facilities with higher-
salinity streams. The red horizontal lines represent the base case 𝑆𝐸𝐶 𝑁𝑒𝑡 for each group and the black dots represent
the influent salinity. All values are for systems without ERDs or CCRO.
3.3.2 𝑆𝐸𝐶 𝑁𝑒𝑡 when using an RO-ERD
To determine whether the 𝑆𝐸𝑆 from an ERD can compensate for the additional RO
energy required from higher-salinity streams, Figure 3-4 shows values of 𝑆𝐸𝐶 𝑁𝑒𝑡 without using
an ERD (the left-hand bar in each pair) alongside values of 𝑆𝐸𝐶 𝑁𝑒𝑡 with using an ERD (the right-
hand bar in each pair); the difference between the left-hand and right-hand bars represent the
𝑆𝐸𝑆 from an ERD. At 0% seawater I&I percentage for the base case (the first pair of the first
group), 𝑆𝐸𝑆 is 0.03 kWh/m
3
. Comparing 𝑆𝐸𝑆 values for the base cases of the five scenarios (the
difference between the left-hand and right-hand bars of the first pair of bars of each group),
shows that 𝑆𝐸𝑆 increases from 0.03 to 0.08 kWh/m
3
as seawater I&I increases from 0 to 10%.
With increasing salinity of the higher-salinity streams, the 𝑆𝐸𝑆 from using an ERD increases as
well. For all scenarios, when the 𝑆𝐸𝐶 𝑁𝑒𝑡 for RO-ERD (the right-hand bar) for each higher-salinity
stream is higher than the red horizontal line, it indicates that the ERD partially compensates for
the additional 𝑆𝐸𝐶 𝑁𝑒𝑡 required to desalinate the higher-salinity feed water. For example, at 0%

43
seawater I&I, the 𝑆𝐸𝑆 from an ERD partially compensates (19-41%) for the additional 𝑆𝐸𝐶 𝑁𝑒𝑡
caused by higher-salinity streams. When the red horizontal line is higher than the 𝑆𝐸𝐶 𝑁𝑒𝑡 for
RO-ERD (the right-hand bar) for each of the higher-salinity streams, the 𝑆𝐸𝑆 from an ERD fully
compensates for the additional energy required to desalinate the higher-salinity feed water. At
10% seawater I&I, when the brine interceptor and BWRO brine 1 are the higher-salinity
streams, the 𝑆𝐸𝑆 from an ERD fully compensates the additional 𝑆𝐸𝐶 𝑁𝑒𝑡 and even leads to lower
𝑆𝐸𝐶 𝑁𝑒𝑡 than the base case. When BWRO brine 2 and BWRO brine 3 are the higher-salinity
streams, the 𝑆𝐸𝑆 from an ERD partially compensates (greater than 70% for BWRO brine 2 and
greater than 30% for BWRO brine 3) for the additional 𝑆𝐸𝐶 𝑁𝑒𝑡 caused by the higher-salinity
stream. Thus, for some scenarios the influent can be augmented (and the brine stream used
beneficially) without additional energy consumption simply by implementing an ERD. In the
future, as higher applied pressures are required to overcome the higher osmotic pressures of
increasing salinity feed streams, greater hydraulic energy can be recovered from the brine
stream and the 𝑆𝐸𝑆 from ERDs will increase. However, achieving energy savings might not be
sufficient to warrant the addition of an ERD to AWPF RO systems; the capital cost of the ERD,
as well as maintenance costs, must be considered in decision-making.

44

Figure 3-4 𝑆𝐸𝐶 𝑁𝑒𝑡 without and with higher-salinity streams for the five seawater I&I scenarios. Bars are paired with
the left-hand bar representing 𝑆𝐸𝐶 𝑁𝑒𝑡 for advanced water purification facilities without an ERD and the right-hand bar
representing 𝑆𝐸𝐶 𝑁𝑒𝑡 for facilities with an ERD. The difference between the left-hand and right-hand bars represents
the energy savings from an ERD. The first pair of bars in each group represents 𝑆𝐸𝐶 𝑁𝑒𝑡 for the base case of each
group and the red horizontal line allows comparison of the base case of each group with the higher-salinity cases.
The black dots represent influent salinity for each pair.
3.3.3 𝑆𝐸𝐶 𝑁𝑒𝑡 when using CCRO
As mentioned earlier, CCRO systems are being considered at AWPFs to improve water
recovery while keeping energy consumption low. In addition, if CCRO is operated at the same
water recovery rates as regular RO, it can also provide 𝑆𝐸𝑆 by decreasing irreversible energy
consumed in RO by operating with time-variant feed pressure. To determine whether the 𝑆𝐸𝑆
from CCRO can compensate for the additional RO energy required from higher-salinity streams,
Figure 3-5 shows values of 𝑆𝐸𝐶 𝑁𝑒𝑡 using regular RO (the left-hand bar in each pair) and values
of 𝑆𝐸𝐶 𝑁𝑒𝑡 using CCRO (the right-hand bar in each pair); the difference between the left-hand
and right-hand bars represent the 𝑆𝐸𝑆 from using CCRO. At 0% seawater I&I percentage for the
base case (the first pair of the first group), 𝑆𝐸𝑆 is 0.03 kWh/m
3
. Comparing 𝑆𝐸𝑆 values for the

45
base cases of the five scenarios (the difference between the left-hand and right-hand bars of the
first pair of bars of each group), shows that 𝑆𝐸𝑆 increases from 0.03 to 0.16 kWh/m
3
as
seawater I&I increases from 0 to 10%. With increasing salinity of the higher-salinity streams, the
𝑆𝐸𝑆 from CCRO increases as well. For all scenarios, when the 𝑆 𝐸𝐶
𝑁𝑒𝑡 for CCRO (the right-hand
bar) for each higher-salinity stream is higher than the red horizontal line, it indicates that the
CCRO partially compensates for the additional 𝑆𝐸𝐶 𝑁𝑒𝑡 required to desalinate the higher-salinity
feed water. For example, at 0% seawater I&I, the 𝑆𝐸𝑆 from CCRO partially compensates (39-
57%) for the additional 𝑆𝐸𝐶 𝑁𝑒𝑡 caused by higher-salinity streams. When the red horizontal line is
higher than the 𝑆𝐸𝐶 𝑁𝑒𝑡 for CCRO (the right-hand bar) for each of the higher-salinity streams, the
𝑆𝐸𝑆 from CCRO fully compensates for the additional energy required to desalinate the higher-
salinity feed water. At 10% seawater I&I, when the brine interceptor, BWRO brine 1, and BWRO
brine 2 are the higher-salinity streams the 𝑆𝐸𝑆 from CCRO fully compensates the additional
𝑆𝐸𝐶 𝑁𝑒𝑡 and even leads to lower 𝑆𝐸𝐶 𝑁𝑒𝑡 than the base case. When BWRO brine 3 is the higher-
salinity stream, the 𝑆𝐸𝑆 from CCRO partially compensates for the additional 𝑆𝐸𝐶 𝑁𝑒𝑡 caused by
the higher-salinity stream (but does compensate for more than 80%). In addition to the energy
savings, the possibility to operate at higher recoveries using CCRO should also be considered.
Even though the 𝑆𝐸𝐶 𝑁𝑒𝑡 , permeate salinity, and brine salinity are higher when operating high-
recovery RO at higher water-recovery (Figure A.2.2 and A.2.3), permeate flowrate increases
and brine discharge flowrate decreases (Figure A.2.4), which would be important in applications
approaching zero liquid discharge.

46

Figure 3-5 𝑆𝐸𝐶 𝑁𝑒𝑡 without and with higher-salinity streams for the five seawater I&I scenarios. Bars are paired with
the left-hand bar representing 𝑆𝐸𝐶 𝑁𝑒𝑡 for advanced water purification facilities using regular RO and the right-hand
bar representing the 𝑆𝐸𝐶 𝑁𝑒𝑡 for advanced water purification facilities using CCRO. The difference between the left-
hand and right-hand bars represents the energy savings from CCRO. The first pair of bars in each group represents
the 𝑆𝐸𝐶 𝑁𝑒𝑡 for the base case of each group and the red horizontal line allows comparison of the base case of each
group with other cases that represent addition of higher-salinity streams. The black dots represent influent salinity for
each pair.

3.3.4 𝑆𝐸𝐶 𝑁𝑒𝑡 when desalinating higher-salinity streams separately from the treated wastewater
To determine whether the 𝑆𝐸𝑆 from desalinating the higher-salinity streams separately
from the treated wastewater could represent a better solution than desalinating the blending
streams, Figure 3-6 shows values of 𝑆𝐸𝐶 𝑁𝑒𝑡 when desalinating higher-salinity streams and
treated wastewater together (indicated by the left-hand bar in each pair) and values of 𝑆𝐸𝐶 𝑁𝑒𝑡
when desalinating higher-salinity streams separately from treated wastewater (indicated by the
righthand bar in each pair); the difference between the left-hand and right-hand bars represent
the 𝑆𝐸𝑆 from separate desalination. There is no right-hand bar for the base case because there
is no stream to desalinate separately. For each seawater I&I percentage, with increasing salinity

47
of the higher-salinity streams, the salinity difference between the treated wastewater and the
higher-salinity streams increases (i.e., the black dot representing salinity difference moves
higher) and the 𝑆𝐸𝑆 increases. For example, at 0% seawater I&I, the 𝑆𝐸𝑆 from separate
desalination increases from an insignificant amount to 0.18 kWh/m
3
. In other words, separate
desalination is substantially more desirable with increasing salinity of the higher-salinity
streams. On the other hand, as seawater I&I increases from 0 to 10%, for a specific higher-
salinity stream, the difference in salinity between the treated wastewater and the higher-salinity
stream decreases (i.e., the black dot moves lower) and the 𝑆𝐸𝑆 decreases. For example, when
BWRO brine 3 is the higher-salinity stream, comparison of 𝑆𝐸𝑆 values for the five seawater I&I
scenarios, shows that 𝑆𝐸𝑆 from separate desalination decreases from 0.18 to 0.08 kWh/m
3
as
seawater I&I increases from 0 to 10%. In other words, separate desalination is substantially
more desirable when the salinity difference is lower. In this analysis, an ERD is not used for the
treated wastewater desalination system or the desalination system for the higher-salinity
stream. Similar to the blended case in Figure 3-4, an ERD could provide additional 𝑆𝐸𝑆 .
Although consideration of separate treatment trains provides a useful basis for comparison and
insight into the effect that salinity difference has on entropy generation, it is noted that agencies
currently discharging brine streams instead of desalinating them on-site do so because they
prefer to pay a discharge fee rather than operate an on-site treatment system.

48

Figure 3-6 𝑆𝐸𝐶 𝑁𝑒𝑡 when desalinating treated wastewater and higher-salinity streams together and separately for the
five seawater I&I scenarios. Bars are paired with the left-hand bar representing the 𝑆𝐸𝐶 𝑁𝑒𝑡 for advanced water
purification facilities when desalinating treated wastewater and higher-salinity streams together and the right-hand bar
representing the 𝑆𝐸𝐶 𝑁𝑒𝑡 for advanced water purification facilities when desalinating higher-salinity streams separately
from treated wastewater. There is no right-hand bar for the base case because there is no stream to desalinate
separately. The difference between the left-hand and right-hand bars represents the energy savings from separate
desalination. The first bar in each group represents the 𝑆𝐸𝐶 𝑁𝑒𝑡 for the base case and the red horizontal line allows
comparison of the base case of each group with other cases that represent addition of higher-salinity streams. The
black dots represent the salinity difference between the higher-salinity stream and treated wastewater.
When desalinating higher-salinity streams and treated wastewater separately, different
RO water recoveries may be desired. In terms of 𝑆𝐸𝐶 𝑁𝑒𝑡 , the most desired RO water-recovery
rates for both treated wastewater and higher-salinity streams are listed in Table A.2.3. At 0%
seawater I&I, there is a greater difference between the desired water-recovery rates for treated
wastewater and the higher-salinity streams due to the greater salinity differences between the
two streams. Mixing of streams with different salinities can increase the levels of entropy leading
to entropy loss (Kim and Hong, 2018). To decrease this entropy loss, higher-salinity streams
should be desalinated separately from treated wastewater when there is a large salinity
difference between two streams. As seawater I&I increases from 0 to 10%, the desired water-

49
recovery rates for both treated wastewater and higher-salinity streams converge on 85%, which
is the overall system water-recovery rate because there is little entropy increase due to mixing
streams.
3.3.5 𝑆𝐸𝐶 𝑁𝑒𝑡 comparison of three energy saving strategies
Comparison of 𝑆𝐸𝐶 𝑁𝑒𝑡 of three energy-saving strategies for a) regional brine interceptor,
b) BWRO brine 1, c) BWRO brine 2, and d) BWRO brine 3 is shown in Figure 3-7. The 𝑆𝐸𝐶 𝑁𝑒𝑡
of three energy-saving strategies, including RO-ERD, CCRO, and desalinating higher-salinity
streams separately are compared with 𝑆𝐸𝐶 𝑁𝑒𝑡 of using RO alone. In most cases, CCRO offers
the greatest energy savings. When using BWRO brine 3 as higher salinity stream, there is
highest salinity difference between higher-salinity stream and treated wastewater, because of
avoiding the highest entropy increase, desalinating separately can compare to CCRO. But when
there is less salinity difference between higher-salinity stream and treated wastewater,
desalinating separately is the least favorable choice, for example, when using regional brine
interceptor, BWRO brine 1, and BWRO brine 2 as higher-salinity streams, RO-ERD is preferred
over desalinating separately. The energy savings from CCRO is at most 2.5 times higher than
the 𝑆𝐸𝑆 from RO-ERD, which happens when using BWRO brine 3 as higher-salinity stream and
at 10% seawater I&I. When using BWRO brine 3 as higher-salinity stream, at 0% seawater I&I,
the order of energy savings from three configurations is: CCRO = desalinating separately > RO-
ERD; at 2.5% and 5% seawater I&I, the order of energy savings from three configurations is:
CCRO > desalinating separately > RO-ERD; at 7.5% and 10% seawater I&I, the order of energy
savings from three configurations is: CCRO > RO-ERD > desalinating separately.

50

Figure 3-7 Comparison of 𝑆𝐸𝐶 𝑁𝑒𝑡 of three energy-saving strategies for a) regional brine interceptor, b) BWRO brine 1,
c) BWRO brine 2, and d) BWRO brine 3. The 𝑆𝐸𝐶 𝑁𝑒𝑡 of three energy-saving strategies, including RO-ERD, CCRO,
and desalinating higher-salinity streams separately are compared with 𝑆𝐸𝐶 𝑁𝑒𝑡 of using RO alone.
3.3.6 Inorganic scaling potential considering seawater I&I and higher-salinity streams
LSI values of RO feed when desalinating the treated wastewater and higher-salinity
streams together and when desalinating higher-salinity streams separately from treated
wastewater are shown in Table A.2.4. The recovery rates were set to 85% for all streams. From
the results, when seawater I&I percentage increases, the LSI of RO feed decreases. By looking
at the ion concentrations in Table A.2.5, this should be caused by the lower concentration of
carbonate ion in seawater than that of treated wastewater. The results also indicated that on the
feed side, BWRO brine 2 have LSI value of zero; BWRO brine 1 has the highest LSI of 1.10;
BWRO brine 3 has the second highest LSI of 0.58; regional brine interceptor has the third
highest LSI of 0.32. According to Table A.2.5, BWRO brine 1 has the highest concentrations for
both calcium and carbonate ions. Even though the salinity of BWRO brine 1 is lower than
BWRO brine 2 and 3, its LSI values indicate that BWRO brine 1 could have highest potential to

51
cause membrane scaling. When desalinating treated wastewater and higher-salinity streams
together lead to LSI values that are lower than that of desalinating higher-salinity streams alone
and higher than that of desalinating treated wastewater streams alone for all cases. In
summary, there are only one cases where the blended streams could result in scaling – when
using BWRO brine 1 as higher-salinity stream. When desalinating treated wastewater and
higher-salinity streams together will lead to LSI values between the two LSI values when
desalinating two streams separately. It shows the benefit of the wastewater diluting the higher-
salinity streams except only a few cases.

3.3.7 Permeate and brine water quality
Permeate salinities for the five seawater I&I scenarios are summarized in Table A.2.6
and Figure A.2.5a. Most permeate salinities are less than the EPA secondary-treated
wastewater effluent standard of 500 mg/L TDS and are expected to be less than most water
quality regulations (e.g., the limit of salinity in recycled water recharged into the OCWD
groundwater basin is 580 mg/L) (Scott-Roberts, 2016). The exceptions occur when BWRO brine
3 is used as higher-salinity stream and seawater I&I percentage is equal or higher than 7.5%,
and the corresponding permeate TDS values are 580 and 660 mg/L, respectively. Brine
salinities for five seawater I&I scenarios are summarized in Table A.2.7 and Figure A.2.5b in
Supplementary Information. Most values are less than typical discharge salinity limits to the
ocean, which are usually set at an increment (e.g., 1 part per thousand) above ambient or at an
absolute level (e.g., 40 g/L) (Jenkins et al., 2012). The only exceptions occur when BWRO brine
3 is used as higher-salinity stream and seawater I&I percentage is equal or greater than 7.5%,
and the corresponding brine TDS values are 42 and 46 g/L, respectively.
3.3.8 Implications
Higher-salinity streams can provide an additional treatment-plant influent that has
undergone pretreatment and likely has lower levels of organics and other constituents than the

52
wastewater they will be blended with. This framework considers how the increased salinity can
be mitigated using ERDs, CCRO, and desalinating high-salinity streams separately; however,
instead of considering the value of ERDs, CCRO, and separate desalination from the standpoint
of energy savings, this analysis considers the additional salinity that can be desalinated, which
may have greater value than energy reduction at AWPFs. Addition of higher-salinity streams
must also be considered within the context of: enhanced source control that ensures known
water quality of the streams, discharge permits that may limit recoveries, and increases in
capital and operating costs that may occur. Further, it must be understood that seawater I&I and
water conservation already result in increased salinity and that both are exacerbated by climate
change. The analysis shows that the rate of 𝑆𝐸𝐶 𝑁𝑒𝑡 change of introducing higher-salinity
streams into potable reuse systems decreases as wastewater salinity increases (e.g., due to
seawater I&I) and that the rate of 𝑆𝐸𝐶 𝑁𝑒𝑡 change is expected to have a decreasing trend in
future years. The results also indicated that with seawater I&I percentages increases, when
introducing higher-salinity streams into the potable reuse systems, the specific energy savings
by using ERD and CCRO increases but the specific energy savings by desalinating higher-
salinity streams separately from treated wastewater decreases. Also, desalinating higher-salinity
stream and treated wastewater separately lead to specific energy saving when the salinity
difference between two streams increases. The framework also provides flexibility whereby
higher-salinity streams may be blended into the AWPF influent instead of the wastewater
treatment facility influent where they can impact biological processes.

Acknowledgement
We acknowledge final support from the University of Southern California’s Theodore and
Wen-Hui Chen Endowed Fellowship, the University of Southern California’s Viterbi/Graduate
School Ph.D. Fellowship to Xin Wei. We thank Jason S. Dadakis from Orange County Water

53
District (OCWD) and Lan C. Wiborg and Mark Kawamoto from Orange County Sanitation
District (OCSD) for useful information about operation details in OCWD and OCSD. We also
thank Jeff Mosher from Santa Ana Watershed Project Authority, Kevin Alexandra from Hazen
and Sawyer, Bob Ohlund from Dudek for providing valuable insight and manuscript feedback.

54
4 CHAPTER 4. Theoretical and Practical Energy
Consumption when Treating Higher-Salinity Wastewaters
for Potable Reuse

4.1 Introduction
Increasing salinity is one of the most important environmental issues of the 21st century.
Rising salinity levels have both environmental and economic costs. Higher salinities can come
from natural processes such as seawater I&I (Werner et al., 2013) and natural weathering
(Srinivasamoorthy et al., 2011), but, like many environmental degradation processes, increasing
salinity is exacerbated by human activities. These include urban runoff, residential water
treatment systems (e.g., water softeners and septic systems), industrial uses (e.g., cooling
towers) (Sardari et al., 2018), agricultural practices (irrigation, fertilizers, and animal wastes),
and water and wastewater treatment systems (e.g., chemicals used in treatment and
concentrated residuals).
4.1.1 Increasing salinity at AWPFs – treatment by RO
As treatment-plant influents have become more saline, desalination by RO in AWPFs
has become more important. Hence, while the role of RO membranes in separating pathogens
and trace organic compounds is still key, the role of RO membranes in separating salts in
potable reuse is being rediscovered as critical.
4.1.2 Energy and water recovery by energy recovery devices and high-recovery RO
High energy costs in the water sector have led many water and wastewater treatment
facilities to include energy management strategies as part of their daily operation (Zohrabian et
al., 2021). For example, energy recovery devices (ERDs) are commonly used in conjunction
with high-salinity RO processes (e.g., SWRO) to reduce the specific energy consumption (𝑆𝐸𝐶 )
of the desalination process (Jeon et al., 2017; Li, 2012; Liu et al., 2016). ERDs reduce energy
consumption by transferring the energy left in RO brine back to the feed stream via centrifugal
55
pumps or positive displacement isobaric devices, such as pressure exchangers and
turbochargers (Kadaj and Bosleman, 2018). ERDs can reduce the energy consumption at
SWRO desalination facilities by as much as 67%, depending on operating conditions. In BWRO
facilities and AWPFs, the low feed water salinity and relatively low brine flowrate make the value
of ERDs ambiguous in terms of cost-effectiveness (Drak and Adato, 2014). Although ERDs are
not commonly used in AWPFs (see Table A.2.1), if higher-salinity streams are considered for
augmenting influent, use of an ERD may provide specific energy savings (𝑆𝐸𝑆 ).
High-recovery RO processes (e.g., closed-circuit reverse osmosis
TM
(CCRO), which is
branded by Desalitech as ReFlex
TM
RO featuring Closed-Circuit Desalination
TM
technology
(Efraty, 2010a; b)) are being considered at AWPFs to improve water recovery while keeping
energy consumption low (Warsinger et al., 2016). CCRO is a semi-batch process in which the
brine is recirculated while water permeates through the RO membrane. Pressurized feed water
is continuously added to the brine, which is not depressurized, and the mixture is returned to the
membrane module to be separated. Once the desired water recovery is reached, the brine
stream is ejected and replaced by new feed solution (Warsinger et al., 2016). For lower-salinity
and lower-brine-flowrate applications, such as BWRO, CCRO can provide greater water and
energy benefits than ERDs (Warsinger et al., 2016). Model results from Warsinger et al. (2016)
predict that CCRO can achieve up to 37% energy savings compared to a standard RO process
for brackish water desalination at high water-recovery. Other than achieving high water-recovery
with reduced energy consumption, CCRO may offer better resistance to fouling and scaling and
operate at higher average fluxes due to higher crossflow velocities (Stover, 2013; 2016).

4.2 Objectives
In Chapter 2, we developed a modeling framework to evaluate synergistic blending of
treated wastewater with SWRO process streams. It was found that potable reuse blending
scenarios, where treated wastewater is blended with intake seawater, lowered energy
56
consumption, seawater intake volume requirements, and discharge volumes compared to
scenarios with seawater only as the influent. In Chapter 3, an inverse scenario – blending
higher-salinity streams with wastewater upstream of RO desalination at an AWPF was
considered. The higher-salinity streams included RO brine streams and regional brine
interceptor/collector streams in both non-I&I and I&I scenarios, where the I&I scenarios include
additional salinity from I&I processes that are common in coastal regions. In this study, the
energy consumed when recovering water if the higher-salinity streams are blended into the
AWPF influent is compared versus the energy consumed in recovering water from the higher-
salinity streams separately and the opportunities to implement or enhance energy and water
recovery using an ERD, an interstage pump between RO stages, and high-recovery RO are
considered.
In the current research, we again consider the scenario of higher-salinity influents to an
AWPF. However, now we quantify the energy consumption of potable reuse of higher-salinity
streams using different energy-recovery strategies. This paper builds on theoretical work that
has been published regarding implementation of ERDs and HRRO and seeks to bridge the gap
between these studies and actual desalination systems pursuing high water and energy
recovery objectives.
The objective of the current study is to quantify the theoretical minimum energy
consumption of RO for three scenarios, 1) using RO alone, 2) using ERDs in conjunction with
RO, and 3) using HRRO instead of RO. Using criteria typical of actual facilities, the existing
theoretical analyses on energy efficiency of RO-ERD and CCRO is extended to evaluate the
best salinity ranges for each technology. In addition, the theoretical minimum energy
consumptions of RO are compared with the practical energy consumptions to quantify the gap
between theoretical minimum energy consumption and practical energy consumption of RO
over a range of salinities and to delineate what the gaps are attributed to. Furthermore, the
inefficiencies that are salinity-related are distinguished from those that are not salinity-related,
57
which provides insight into how to bring the practical energy consumption closer to the
theoretical energy consumption of RO.

4.3 Material and methods
4.3.1 Modeling system
By considering the water portfolio, both treated wastewater and seawater are possible
influent streams. The world-average salinity of seawater (34.4 g/L (Ocean Health, 2020)) is
used as seawater salinity and 1.2 g/L is used is used as the secondary-treated wastewater
effluent (AWPF influent) salinity (section 3.2.1 in Chapter 3). Depending on the possible
availabilities of the two streams, the salinities considered in this research is from 1.2 to 35 g/L.
4.3.2 Thermodynamic energy efficiency for the RO process
Thermodynamic energy efficiency (TEE) is the ratio between Gibbs free energy for
separation (𝛥 𝐺 ) theoretically consumed by the thermodynamically reversible desalination
process and the actual 𝑆𝐸𝐶 of the desalination process (RO in our case) (Sharqawy et al.,
2011). Actual 𝑆𝐸𝐶 is greater than Δ𝐺 due to the losses or irreversibility of components in the
system (Mistry et al., 2011). The maximum TEE (𝑇𝐸𝐸 𝑚𝑎𝑥 ) is achieved when the lowest
allowable pressure is applied to achieve the target water-recovery. 𝑇𝐸𝐸 𝑚𝑎𝑥 is calculated
using:(Lin, 2020)
𝑇𝐸𝐸 𝑚𝑎𝑥 =
𝛥 𝐺 𝑆𝐸𝐶 𝑚𝑖𝑛 (4.1)
For an RO process, the maximum TEE (𝑇𝐸𝐸 𝑅𝑂 ,𝑚𝑎𝑥 ) is calculated using (Lin, 2020):
𝑇𝐸𝐸 𝑅𝑂 ,𝑚𝑎𝑥 = (1 − 𝑊𝑅 )ln (
1
1−𝑊𝑅
) (4.2)
where 𝑊𝑅 is water recovery.
For an RO process using an ERD with 100% efficiency, the maximum TEE (𝑇𝐸𝐸 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑎𝑥 ) is
calculated using (Lin and Elimelech, 2015):
58
𝑇𝐸𝐸 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑎𝑥 =
1−𝑊𝑅
𝑊𝑅
ln (
1
1−𝑊𝑅
) (4.3)
To estimate the energy consumption by CCRO, it was assumed that RO with four or more
stages closely approaches CCRO (Lin and Elimelech, 2015) and a four-stage RO system was
adapted from a 3-stage RO system (Lin, 2020). For the CCRO process, the maximum TEE
(𝑇𝐸𝐸 𝐶𝐶𝑅𝑂 ,𝑚𝑎𝑥 ) is estimated by calculating the TEE for a 4-stage RO using an equation adapted
from Lin (Lin and Elimelech, 2015):
𝑇𝐸𝐸 𝐶𝐶𝑅𝑂 ,𝑚𝑎𝑥 ≈ 𝑇𝐸𝐸 4−𝑠𝑡𝑎𝑔𝑒 𝑅𝑂
= ln (
1
1−𝑊𝑅
)
4
(
4
4−𝑊𝑅
+
2
2−𝑊𝑅
+
4
4−3𝑊𝑅
+
1
1−𝑊𝑅
)
(4.4)
4.3.3 Minimum specific energy consumption for the RO process
Rearranging Equation (4.1), the minimum energy consumption (𝑆𝐸𝐶 𝑚𝑖𝑛 ) for the RO, RO-
ERD, or CCRO process is calculated using:
𝑆𝐸𝐶 𝑚𝑖𝑛 =
𝛥 𝐺 𝑇𝐸𝐸 𝑚𝑎𝑥
(4.5)
𝛥 𝐺 is calculated using (Lin and Elimelech, 2015):
𝛥 𝐺 =
𝜋 0
𝑊𝑅
ln (
1
1−𝑊𝑅
) (4.6)
where 𝜋 0
is feed osmotic pressure, which, for an ideal solution is calculated using the van’t Hoff
equation (Murad and Powles, 1993; Van't Hoff, 1888):
𝜋 0
=
𝑛𝑅𝑇 𝑉 = 𝑚𝑅𝑇 (4.7)
where n is number of moles of solute, V is volume of solution, 𝑚 =
𝑛 𝑉 is molar concentration of
the solute, R is the ideal gas constant (0.0821 𝐿 ∙ 𝑎𝑡𝑚 ∙ 𝑚𝑜𝑙
−1
𝐾 −1
), and T is temperature (298
K).
4.3.4 Practical specific energy consumption of RO calculated by WAVE software and its
comparison between theoretical minimum specific energy consumption of RO
All simulations were based on a large AWPF with capacity of 174 MGD. A framework,
similar to that developed in our previous study (i.e., Wei et al. (2020)) was used. The RO
process was modeled using DOW
TM
WAVE design software (DuPont Water Solution, 2020).
59
The RO membrane module modeled in this research was the BW30XFRLE-400/34i module
(DuPont Water Solutions, Edina, MN), which is suitable for both potable water reuse and
industrial water demineralization. The RO water-recovery was set to 85% based on the system
recoveries for large-scale AWPFs (Bartels et al., 2005; DUPONT, 2021; Scott-Roberts, 2016).
The RO system was modeled to include 20 trains with each train having a two-stage array. In
stages 1 and 2, there are 60 and 20 vessels, respectively; each vessel contains seven
membrane elements. The RO 𝑆𝐸𝐶 modeled by WAVE is labeled as 𝑆𝐸𝐶 𝑚𝑖𝑛 ,𝑊𝐴𝑉𝐸 . Comparing
𝑆𝐸𝐶 𝑅𝑂 ,𝑊𝐴𝑉𝐸 with 𝑆𝐸𝐶 𝑚𝑖𝑛 , 𝑆𝐸𝐶 𝑅𝑂 ,𝑊𝐴𝑉𝐸 also considers, to some extent, the 𝑆𝐸𝐶 caused by non-
idealities in practical usage.

4.4 Results and discussions
4.4.1 Thermodynamic energy efficiency comparison between RO alone, RO-ERD, and CCRO
CCRO is being used, or considered for use, at AWPFs to achieve high water-recovery
with reduced energy consumption. Maximum thermodynamic energy efficiency, 𝑇𝐸𝐸 𝑚𝑎𝑥 , values
for the CCRO (𝑇𝐸𝐸 𝐶𝐶𝑅𝑂 ,𝑚𝑎𝑥 ) process in comparison with the RO (𝑇𝐸𝐸 𝑅𝑂 ,𝑚𝑎𝑥 ) and RO-ERD
(𝑇𝐸𝐸 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑎𝑥 ) processes are shown in Figure 4-1a, which is adapted from Lin et al. (2020).
Also shown are typical water-recovery ranges for SWRO and AWPF RO processes; typical
water-recoveries for SWRO range from 40 to 50% (Kim et al., 2020) and for AWPF RO from 60
to 90% depending on feed salinity (Owens et al., 2014; Pan et al., 2020). From Figure 4-1a, at
an 85% water recovery, which is common at several large-scale AWPF RO systems (Al-Obaidi
et al., 2020; Pan et al., 2020), 𝑇𝐸𝐸 𝐶𝐶𝑅𝑂 ,𝑚𝑎𝑥 , 𝑇𝐸𝐸 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑎𝑥 , and 𝑇𝐸𝐸 𝑅𝑂 , 𝑚𝑎𝑥 are 0.60, 0.33, and
0.28. As expected, CCRO and RO-ERD processes increase energy efficiency. It can generally
be seen that when water recovery is less than 65%, such as in RO systems for seawater
desalination or brine treatment, RO-ERD is preferred and when water recovery is greater than
65%, such as in RO systems for brackish water or wastewater reclamation, CCRO is preferred
60
to improve energy efficiency (Lin, 2020). It can also be seen that the maximum TEE is
approximately 81%; this could suggest that CCRO systems should target a lower recovery than
they currently do (at 85% and higher); however, at AWPFs, higher water-recovery may be more
important than a slight reduction in energy consumption. On the other hand, if high water-
recoveries become limited by brine discharge regulations, operating at a water-recovery rate
closer to 80% may achieve multiple objectives.

Figure 4-1 (a) Theoretical maximum thermodynamic energy efficiency as a function of RO water-recovery (adapted
from Lin et al.(Lin, 2020)) and (b) theoretical maximum thermodynamic energy efficiency as a function of salinity for
scenarios using CCRO, RO-ERD, and RO alone. Figure 4-1 (b) is adapted from Figure 4a with the following
assumptions: 85% water recovery for AWPF RO (with 1.2 g/L as feed salinity), 50% water recovery for SWRO (with
34.4 g/L as feed salinity) (Wei et al., 2020), and a linear relationship between feed salinity and water recovery.
By graphing 𝑇𝐸𝐸 𝑚𝑎𝑥 as a function of salinity (Figure 4-1b), the best salinity ranges for
each technology can be better distinguished for this case study. Values in Figure 4-1b
assume: 85% water recovery for AWPF RO (with 1.2 g/L as feed salinity), 50% water recovery
for SWRO (with 34.4 g/L as feed salinity), and a linear relationship between feed salinity and
water recovery. To depict a linear relationship, blended RO feed streams are considered, with
recovery rates that are weighted averages between SWRO and APWF RO water-recoveries
as given by Wei et al. (2020). Under these assumptions, a feed salinity of approximately 20.2
g/L (a water recovery of 65%) delineates the region where CCRO is preferred (when feed
61
salinity is less than 20.2 g/L) and where RO-ERD is preferred (when feed salinity is greater
than 20.2 g/L). The graph of TEE as a function of salinity is useful for cases such as the
current study where salinities exceed typical AWPF salinities and don’t fall squarely into
traditional recovery categories. In this case study, even with blending higher-salinity streams
into seawater I&I scenarios, all of the AWPF feedwater salinities remain in the “CCRO
preferred” region. However, the cost and complexity of retrofitting an RO system with
implementing high-recovery RO (e.g., CCRO or an alternative configuration such as adding
an additional stage or brine concentrator to a conventional RO system) must be considered in
comparison with the simplicity of implementing an ERD; if this is considered, RO-ERD may be
preferable at salinities less than the 20.2 g/L delineation. And eventually, increased salinity
due to climate change impacts, may result in AWPF feedwater salinities reaching or
exceeding 20.2 g/L. For sure, the delineation may be reached or exceeded for other case
studies where higher salinity streams are considered.
4.4.2 RO minimum specific energy consumption between RO alone, RO-ERD, and CCRO
The two-dimensional contours in Figure 4-2 represent 𝑆𝐸𝐶 𝑚𝑖𝑛 values for different
combinations of water recovery and feed salinity for RO (Figure 4-2a), RO-ERD (Figure 4-2b),
and CCRO (Figure 4-2c). In Figure 4-2a, 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛 reaches the peak value at both low and high
water-recoveries. Regarding the peak value at low water-recovery, this occurs because at low
water-recovery, 𝑄 𝐹𝑒𝑒𝑑 must be high to maintain a constant 𝑄 𝑃𝑒𝑟𝑚𝑒𝑎𝑡𝑒 . According to (Zhu et al.,
2009):
𝑆𝐸𝐶 𝑅𝑂
=
∆𝑃 ×𝑄 𝐹𝑒𝑒𝑑 𝑄 𝑃𝑒𝑟𝑚𝑒𝑎𝑡𝑒 =
∆𝑃 𝑊𝑅
(4.8)
high 𝑄 𝐹𝑒𝑒𝑑 results in high energy-consumption. Regarding the peak value at high water-
recovery, 𝑄 𝐹𝑒𝑒𝑑 is much less than it is at low water-recovery; however, the brine osmotic
pressure (∆π
𝐵𝑟𝑖𝑛𝑒 ) is much greater than it is at low water-recovery. Given that during the RO
process, ∆𝑃 must always be greater than ∆π
𝐵𝑟𝑖𝑛𝑒 :
62
∆𝑃 ≥ ∆π
𝐵𝑟𝑖𝑛𝑒 ∝ 𝑆𝑎𝑙𝑖𝑛𝑖𝑡𝑦 𝐵𝑟𝑖𝑛𝑒 ≈ 𝑆𝑎𝑙𝑖𝑛𝑖𝑡𝑦 𝐹𝑒𝑒𝑑 /(1 − 𝑊𝑅 ) (4.9)
the high ∆𝑃 results in the energy consumption peak value. Also, at high water-recovery, ∆𝑃 is
much greater than the feed osmotic pressure (∆π
𝐹𝑒𝑒𝑑 )(Cordoba et al., 2021) and this “over-
pressure” (∆𝑃 − ∆π
𝐹𝑒𝑒𝑑 ) results in inefficiency that is mitigated by staging (Li, 2010; Werber et
al., 2017) and more recently, by CCRO processes.

Figure 4-2 Comparison of 𝑆𝐸𝐶 𝑚𝑖𝑛 of three configurations for a) RO alone, b) RO-ERD and c) CCRO with water-
recovery rates ranging from 5 to 95% and salinities ranging from 0 to 40 g/L. The contour lines indicated all points of
which are at the same 𝑆𝐸𝐶 𝑚𝑖𝑛 values. Both the color of the contour line and the number labeled on the contour line
indicated the value of 𝑆𝐸𝐶 𝑚𝑖𝑛 representing a specific line.
In Figure 4-2b, all values of 𝑆𝐸𝐶 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑖𝑛 are less than 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛 (Figure 4-2a) by a
factor of WR. RO-ERD energy consumption (assuming 100% ERD efficiency) is calculated
using (Lin, 2020):
𝑆𝐸𝐶 𝑅𝑂 −𝐸𝑅𝐷 = 𝑆𝐸𝐶 𝑅𝑂
× 𝑊𝑅 = ∆𝑃 (4.10)
which results in values that differ from those in Eq 3-2-1 by a factor of WR. Equation (4.10) also
shows that at low water-recovery, there would be no peak in 𝑆𝐸𝐶 𝑅𝑂 −𝐸𝑅𝐷 .
In Figure 4-2c, all values of 𝑆𝐸𝐶 𝐶𝐶𝑅𝑂 ,𝑚𝑖𝑛 are less than those for 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛 (see Table
A.3.1). 𝑆𝐸𝐶 𝐶𝐶𝑅𝑂 ,𝑚𝑖𝑛 has peak values at low water-recovery for the same reason that 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛
peak values at low water-recovery – because of the high 𝑄 𝐹𝑒𝑒𝑑 required; however, 𝑆𝐸𝐶 𝐶𝐶𝑅𝑂 ,𝑚𝑖𝑛
is slightly less than 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛 . For example, at a WR of 5%, the 𝑆𝐸𝐶 𝐶 𝐶 𝑅𝑂 ,𝑚𝑖𝑛 is 2% less than
𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛 . At high water-recovery, the CCRO process significantly reduces the over-pressure so
𝑆𝐸𝐶 𝐶𝐶𝑅𝑂 ,𝑚𝑖𝑛 is much less than 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛 . Also, at high water-recovery rates (e.g., 85%, which is
63
typical for CCRO processes) Figure 4-2c shows that the 𝑆𝐸𝐶 value increases as more permeate
water is produced, representing the energy-water tradeoff. If an AWPF has chosen to use a
CCRO process, it is likely that the facility would prefer production of more product water and/or
less brine and be less concerned with achieving the highest energy efficiency.
4.4.3 Salinity related and non-salinity related non-idealities between 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛 and 𝑆𝐸𝐶 𝑅𝑂 ,𝑊𝐴𝑉𝐸
In Figure 4-3, 𝑆𝐸𝐶 𝑚𝑖𝑛 values for the three systems (𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛 , 𝑆𝐸𝐶 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑖𝑛 ,
𝑆𝐸𝐶 𝐶𝐶𝑅𝑂 ,𝑚𝑖𝑛 ) are shown for a water recovery of 85% along with the 𝑆𝐸𝐶 𝑅𝑂
calculated by WAVE
design software. Data points from WAVE design software are shown along with a best-fit line
(R
2
= 0.996). By comparing 𝑆𝐸𝐶 𝑅𝑂
with 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛 at a salinity of 0 g/L, the SEC associated with
non-salinity related non-idealities is clearly indicated for the first time. Non-salinity related non-
idealities include inefficiencies of pumps, membrane fouling and scaling, and deterioration of
membrane performance with age (Donose et al., 2013; Jiang et al., 2017; Zhu et al., 2009). As
salinity increases, salinity-related non-idealities, such as concentration polarization and non-
ideal thermodynamic effects on observed salt diffusion coefficients (Jang et al., 2019; Kamcev
et al., 2017), increase the gap between 𝑆𝐸𝐶 𝑅𝑂
and 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛 . Also, as salinity increases, the
benefit of using RO-ERD or CCRO increases. For example, at a feed salinity of 2.8 g/L
(representing the 5% seawater I&I scenario), using RO-ERD reduces 𝑆𝐸𝐶 by 15% and using
CCRO reduces 𝑆𝐸𝐶 by 54%. Perhaps more importantly, we can consider the benefit of using
RO-ERD or CCRO from the x-axis standpoint – the additional salinity that can be treated
(instead of the y-axis standpoint of energy savings). At a feed salinity of 2.8 g/L, simply by
implementing an ERD, we could treat an additional 0.47 g/L of salinity with no additional energy
consumption. If we retrofit with a CCRO system, we could treat an additional 3.2 g/L (0.47+2.73
g/L) of salinity with no additional energy consumption. From this perspective, we can consider
the horizontal lines representing 0.47 and 3.2 g/L as measures of energy-free desalination of
higher-salinity streams.
64

Figure 4-3 Comparison of 𝑆𝐸𝐶 𝑅𝑂
calculated by WAVE design software with 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛 enables clear identification of
regions where salinity-related non-idealities and non-salinity related non-idealities result in modeled SEC being
greater than theoretical minimum SEC. Also shown are two regions below the 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛 line that indicate where
implementation of an ERD or transition to high-recovery RO (e.g., CCRO) enables removal of additional salinity with
no additional energy consumption. The horizontal lines representing 0.47 and 3.2 g/L are measures of energy-free
desalination of higher-salinity streams by using ERD-RO or CCRO.

4.5 Implications
This framework considers how the increased salinity can be mitigated using ERDs and
CCRO; however, instead of considering the value of ERDs and CCRO from the standpoint of
energy savings, this analysis considers the additional salinity that can be treated, which may
have greater value than energy reduction at AWPFs. In addition to the framework, this chapter
builds on theoretical work that has been published regarding implementation of ERDs and
CCRO and compares the theoretical minimum energy consumption of RO with the practical
energy consumptions to investigate the inefficiencies that can be targeted to bring the practical
energy consumption closer to the theoretical energy consumption of RO. The results
distinguished that the best salinity ranges to implement RO-ERD and CCRO. A feed salinity of
approximately 20.2 g/L (a water recovery of 65%) delineates the region where CCRO is
preferred (when feed salinity is less than 20.2 g/L) and where RO-ERD is preferred (when feed
salinity is greater than 20.2 g/L). However, the cost and complexity of retrofitting an RO system
with implementing high-recovery RO (e.g., CCRO or an alternative configuration such as adding
65
an additional stage or brine concentrator to a conventional RO system) must be considered in
comparison with the simplicity of implementing an ERD.

66
5 CHAPTER 5. Conclusions

5.1 Research synopsis
This dissertation presents investigations into synergistic systems for desalination and
potable reuse and focus on the novel configurations and energy consumption. These
investigations include: (1) building a modeling framework to evaluate blending of seawater and
treated wastewater streams for synergistic desalination and potable reuse, (2) potable reuse
treatment of reclaimed wastewater with increasing salinity, (3) seawater augmented advanced
water purification facilities.

5.2 Major contributions
5.2.1 Summary of modeling framework to evaluate blending of seawater and treated
wastewater streams for synergistic desalination and potable reuse
This dissertation indicated the benefits that potable reuse brought in seawater
desalination. The synergistic blending of the waste streams from SWRO desalination and the
nearby wastewater treatment facilities was evaluated. Four scenarios were evaluated in the
framework. In the first two scenarios, the treated wastewater is blended with the brine resulting
from SWRO process, which effectively diluting SWRO brine before it’s discharged to the ocean.
One of the scenarios also considers the saving by capturing the salinity-gradient energy. In the
other two scenarios, the treated wastewater is blended with the seawater intake in order to
dilute the influent to SWRO process. One of the scenarios incorporate a low-energy osmotic
dilution process as a pretreatment barrier for the wastewater. The required seawater and
treated wastewater flowrates, discharge flowrates and components, boron removal, and net
energy consumptions are evaluated. Based on the results, the two influent blending scenarios
have multiple advantages over the brine blending scenarios. The benefits include 1) less
67
seawater intake and brine discharge flowrates, 2) no need for second-pass RO targeting boron
control, and 3) less energy consumption (Wei et al., 2020). Even though the evaluation is based
on co-located SWRO facility and its nearby wastewater reclamation facility, the framework could
also be extended for use in in-land facilities where disposal of RO brine is an issue (Wei et al.,
2020).
5.2.2 Summary of potable reuse treatment of reclaimed wastewater with increasing salinity
This dissertation estimated the impacts of seawater inflow & infiltration and higher-
salinity streams on potable reuse. Higher-salinity streams can provide an additional treatment-
plant influent that has undergone pretreatment and likely has lower levels of organics and other
constituents than the wastewater they will be blended with. This framework considers how the
increased salinity can be mitigated using ERDs, CCRO, and treating streams separately;
however, instead of considering the value of ERDs, CCRO, and separate RO trains from the
standpoint of energy savings, this analysis considers the additional salinity that can be treated,
which may have greater value than energy reduction at AWPFs. Addition of higher-salinity
streams must also be considered within the context of: enhanced source control that ensures
known water quality of the streams, discharge permits that may limit recoveries, and increases
in capital and operating costs that may occur. Further, it must be understood that seawater I&I
and water conservation already result in increased salinity and that both are exacerbated by
climate change. The analysis shows that the rate of 𝑆𝐸𝐶 𝑁𝑒𝑡 change of introducing higher-salinity
streams into potable reuse systems decreases as wastewater salinity increases (e.g., due to
seawater I&I) and that the rate of 𝑆𝐸𝐶 𝑁𝑒𝑡 change is expected to have a decreasing trend in
future years. The results also indicated that implementation of energy recovery device or
transition to CCRO enables removal of additional salinity at no additional energy cost and the
scaling potential in higher-salinity streams can also be mitigated by the dilution of treated
wastewater. The framework also provides flexibility whereby higher-salinity streams may be
68
blended into the AWPF influent instead of the wastewater treatment facility influent where they
can impact biological processes.
5.2.3 Summary of energy consumptions for seawater augmented advanced water purification
facilities
This dissertation considers how the increased salinity can be mitigated using ERDs and
CCRO based on both theoretical minimum energy consumption and practical energy
consumptions and distinguished the preferred salinity ranges for both RO-ERD and CCRO. This
paper builds on theoretical work that has been published regarding implementation of ERDs and
CCRO and compares the theoretical minimum energy consumption of RO with the practical
energy consumptions to investigate the inefficiencies that can be targeted to bring the practical
energy consumption closer to the theoretical energy consumption of RO.
By investigating energy efficiency as a function of salinity, the best salinity ranges to
implement RO-ERD and CCRO were distinguished. A feed salinity of approximately 20.2 g/L (a
water recovery of 65%) delineates the region where CCRO is preferred (when feed salinity is
less than 20.2 g/L) and where RO-ERD is preferred (when feed salinity is greater than 20.2 g/L).
In this case study, even with blending higher-salinity streams into seawater I&I scenarios, all of
the AWPF feedwater salinities remain in the “CCRO preferred” region. However, the cost and
complexity of retrofitting an RO system with implementing high-recovery RO (e.g., CCRO or an
alternative configuration such as adding an additional stage or brine concentrator to a
conventional RO system) must be considered in comparison with the simplicity of implementing
an ERD; if this is considered, RO-ERD may be preferable at salinities less than the 20.2 g/L
delineation. And eventually, increased salinity due to climate change impacts, may result in
AWPF feedwater salinities reaching or exceeding 20.2 g/L. For sure, the delineation may be
reached or exceeded for other case studies where higher salinity streams are considered. Also,
at salinity of 0 g/L, there exists non-salinity-related non-idealities, which may include
inefficiencies of pumps, membrane fouling and scaling, and deterioration of membrane
69
performance with age. As salinity increase, there is salinity-related non-idealities, which may
contain concentration polarization and non-ideal thermodynamic effects on observed salt
diffusion coefficients. Also, as salinity increases, the benefit of using RO-ERD or CCRO
increases.

5.3 Impacts and implications
This dissertation built comprehensive framework considering multiple options to utilize
desalination and potable reuse synergistically. Under climate change, less fresh water and more
saline water sources leads to increased energy consumption for water supply. At the same time,
higher energy consumptions accelerate the climate change. The work in this dissertation
explored the integrated systems of desalination and potable reuse with reduced energy
consumption for increased water supply. From the different facilities’ perspectives, this study
critically investigated benefits of combining desalination and potable reuse in terms of energy
consumption, water quality, scaling potential, and environmental impacts. This study also built
on theoretical work published for ERDs and CCRO and bridged gap between previous studies
and actual desalination and potable reuse systems that are pursuing high water- and energy-
recovery objectives. In addition, this dissertation built the cornerstone of framework to evaluate
future blending scenarios for saline and waste waters, including wastewater-augmented
seawater desalination and seawater-augmented potable reuse.

70
6 Appendix A: Supplementary Information
A.1 Supplementary Information to Chapter 2
A.1.1 Scenarios description
Four scenarios were considered in this study. In all scenarios, a pressure exchanger is
incorporated to reduce energy consumption. In Scenarios 1 and 2 (Figs. S.1 and S.2), the intake
seawater is treated using ultrafiltration (UF) and reverse osmosis (RO). Post-treatment consists
of disinfection and remineralization. The RO brine is blended with treated wastewater
(secondary effluent) in order to meet the 40 g/L limitation on discharge salinity that was set in
this study. In Scenario 2 (Fig. S.2), pressure-retarded osmosis is used to recover salinity
gradient energy (SGE) from the blending of the RO brine (70 g/L) and treated wastewater (0.6
g/L). The treated wastewater is treated by UF prior to the pressure-retarded osmosis process. In
Scenarios 3 and 4 (Figs. S.3 and S.4), the treated wastewater is blended with the intake
seawater upstream of the RO process. Because these are potable reuse scenarios, UV/H2O2 is
used as post-treatment to oxidize neutral-charged, low-molecular-weight organics that pass
through the RO membrane. In Scenario 4 (Fig. S.4), osmotic dilution uses the salinity difference
between the seawater (35 g/L) and treated wastewater (< 0.6 g/L) to provide a low-energy pre-
treatment for the treated wastewater.
71

Figure A.1.1 Scenario 1 (baseline scenario) – blending treated wastewater with RO brine.

Figure A.1.2 Scenario 2 – blending treated wastewater with RO brine and extracting salinity-gradient energy.
Scenario 1

Scenario 2

Flowrate of UF filtrate = flowrate of treated
wastewater needed for salinity gradient energy
recovery

72

Figure A.1.3 Scenario 3 – blending treated wastewater with seawater influent.

Figure A.1.4 Scenario 4 – blending treated wastewater with seawater influent using osmotic dilution.

A.1.2 Energy consumption of pre-treatment
UF is used for pre-treating seawater in all scenarios and for pre-treating treated
wastewater in Scenarios 3 and 4. As illustrated in Fig. S.5, when the SW:WW ratio decreases,
the UF SEC for treated wastewater pre-treatment increases and the UF SEC for seawater pre-
Scenario 3

Flowrate of UF filtrate = flowrate of treated
wastewater needed for influent dilution
Scenario 4

73
treatment decreases. The total UF SEC decreases from 0.14 to 0.088 kWh/m
3
of product water
as the SW:WW ratio decreases from 100:0 to 0:100.

Figure A.1.5 UF energy consumption for pre-treatment as a function of seawater:treated wastewater (SW:WW)
influent ratios.

74
A.2 Supplementary Information to Chapter 3
A.2.1 Selection of RO advanced water purification facilities in California and whether or not an
energy recovery device is used
Table A.2.1 Summary of RO advanced water purification facilities in California and whether or not an energy recovery
device (ERD) is used
No
.
Project name Plant status Online date Capacity
(MGD)
Customer type ERDs
installed
Reference
1 Orange County
Water District
Groundwater
Replenishment
System
Online 2015 100 Groundwater
replenishment
Yes (Global Water
Intelligence
(GWI), 2021)
2 Edward C. Little
Water Recycling
Facility
Online 2013 40 Groundwater
replenishment
No (Global Water
Intelligence
(GWI), 2021)
3 Pure Water
Monterey
Online 2019 9.24 Groundwater
replenishment
No (US
Environmenta
l Protection
Agency (US
EPA), 2019)
4 Albert Robles
Center for Water
Recycling &
Environmental
Learning
Online 2019 8.9 Groundwater
replenishment
No (Global Water
Intelligence
(GWI), 2021)
5 Leo J Vander Lans
Advanced Water
Treatment Facility
Expansion
Online 2014(Globa
l Water
Intelligence
(GWI),
2021)
8 Groundwater
replenishment
Yes (Global Water
Intelligence
(GWI), 2021)
6 San Luis Rey
Wastewater
Treatment Plant
Under
constructio
n
2022 6 Groundwater
replenishment
No (Global Water
Intelligence
(GWI), 2021)
7 Silicon Valley
Advanced Water
Treatment Plant
Online 2014 8 Groundwater
replenishment
No (Global Water
Intelligence
(GWI), 2021)
8 Morro Bay Water
Reclamation Facility
Under
constructio
n
2023 1 Groundwater
replenishment
No (Atkinson,
2020)
9 LA Advanced Water
Purification Facility
Online 2019 0.5 Groundwater
replenishment
No (Regional
Recycled
Water
Advanced
Purification
Center, 2021)
10 Advanced Water
Purification Facility
for the City of
Oxnard
Online 2015 6.25 Irrigation and
groundwater
recharge
No (Lozier and
Ortega, 2010)
11 Terminal Island
Water Reclamation
Facility
Online 2002 6 Groundwater
recharge
Yes (Global Water
Intelligence
(GWI), 2021)
12 Carmel Area Water
District
Online 2015 1 Irrigation No (Global Water
Intelligence
(GWI), 2021)
75
13 Westside Recycled
Water Project
Online 2019 2 Irrigation and
lake fill
No (Global Water
Intelligence
(GWI), 2021)
14 Escondido Recycled
Water Treatment
Plant
Under
constructio
n
2021 2 Irrigation No (Global Water
Intelligence
(GWI), 2021)
15 Rainbow Municipal
Water District
Online 2009 7 Irrigation No (Global Water
Intelligence
(GWI), 2021)
16 Beaumont Salt
Mitigation Facility
Online 2020 6 Irrigation No (Global Water
Intelligence
(GWI), 2021)
17 Carlsbad Municipal
Water District Water
Recycling Facility
Online 2008 4 Irrigation No (Carlsbad
Municipal
Water District,
2012)
18 Carlsbad Municipal
Water District WRF -
Phase III
Online 2017 3 Irrigation Yes (Global Water
Intelligence
(GWI), 2021)
19 Carmel Area Water
Authority facility in
Pebble Beach
Online 2008 1.6 Irrigation No (Global Water
Intelligence
(GWI), 2021)
20 Carmel Area
Wastewater Facility
Online 2008 1.2 Irrigation No (Global Water
Intelligence
(GWI), 2021)
21 San Pasqual Water
Recycling Facility
Under
constructio
n
2021 1 Irrigation No (Global Water
Intelligence
(GWI), 2021)
22 EBMUD Richmond
Advanced Recycled
Expansion Water
Project
Online 2010 6 Industry No (Global Water
Intelligence
(GWI), 2021)
23 Demonstration of
the San Diego
Advanced Water
Purification Facility
Online 2011 1 Surface water
augmentation
No (Global Water
Intelligence
(GWI), 2021)

A.2.2 Salinities of secondary effluents serving as influent for selected advanced water
purification facilities
Table A.2.2 Example Water Treatment Facilities Producing Water of Potable Reuse Quality
Facility Capacity
(MGD)
TDS
(mg/L)
Reference
Groundwater Replenishment
System, CA, USA
100 1,167 (Al-Obaidi et al., 2020)
Edward C. Little Water Recycling
Facility, CA, USA
40 900 (Lazarova et al., 2003)

Ulu Pandan NEWater Plant,
Singapore
95 677 (Al-Obaidi et al., 2020)
Sulaibiya Wastewater Treatment
and Reclamation Facility, Kuwait*
82 1,280 (Alhumoud et al., 2010)
*specifications of the reclaimed water produced from this facility exceed World Health Organization standards for
potable water; however, the reclaimed water is currently used for agricultural and industrial applications.
1

76

A.2.3 Rate of 𝑆𝐸𝐶 𝑁𝑒𝑡 change of introducing higher-salinity streams
The rate of 𝑆𝐸𝐶 𝑁𝑒𝑡 is defined as the following equation:
𝑅𝑎𝑡𝑒 𝑜𝑓 𝑆𝐸𝐶 𝑁𝑒𝑡 = ∆𝑆𝐸𝐶 𝑁𝑒𝑡 /∆𝑆𝑎𝑙𝑖𝑛𝑖𝑡𝑦 =
𝑆𝐸𝐶 𝑁𝑒𝑡 𝑤𝑖𝑡 ℎ ℎ𝑖𝑔 ℎ𝑒𝑟 −𝑠𝑎𝑙𝑖𝑛𝑖𝑡𝑦 𝑠𝑡𝑟𝑒𝑎𝑚 − 𝑆𝐸𝐶 𝑁𝑒𝑡 𝑤𝑖𝑡 ℎ𝑜𝑢𝑡 ℎ𝑖𝑔 ℎ𝑒𝑟 −𝑠𝑎𝑙𝑖𝑛𝑖𝑡𝑦 𝑠𝑡𝑟𝑒𝑎𝑚 𝑆𝑎𝑙𝑖𝑛𝑖𝑡𝑦 𝐻𝑖𝑔 ℎ𝑒𝑟 −𝑠𝑎𝑙𝑖𝑛𝑖𝑡𝑦 𝑠𝑡𝑟𝑒𝑎𝑚 − 𝑆𝑎𝑙𝑖𝑛𝑖𝑡𝑦 𝑇𝑟𝑒𝑎𝑡𝑒𝑑 𝑤𝑎𝑠𝑡𝑒𝑤𝑎𝑡𝑒𝑟

Figure A.2.1 Rate of 𝑆𝐸𝐶 𝑁𝑒𝑡 change of introducing four types of higher-salinity streams for the five seawater I&I
scenarios.

77
A.2.4 Flowrates, energy consumption, and permeate and brine salinities when using high-
recovery RO with water-recovery of 95%
The high-recovery RO process was modeled using DOW
TM
WAVE design software
(DuPont Water Solution, 2020). The RO membrane module modeled in this research was the
FilmTec
TM
SOAR-4000 (DuPont Water Solutions, Edina, MN. The high-recovery RO system was
modeled to include 26 trains with each train having a one-stage array. There are 122 vessels in
each stage; each vessel contains seven membrane elements. The high-recovery RO water-
recovery was set to 95% based on the system recoveries for large-scale AWPFs (DuPont Water
Solutions, 2021). The 𝑆 𝐸𝐶
𝑁𝑒𝑡 with water-recovery rate of 95% is shown in Figure A.2.2. The
permeate and brine salinity without and with higher-salinity streams for the five seawater I&I
scenarios when using regular RO (with water-recovery of 85%) and high-recovery RO (with
water-recovery of 95% were should in Figure A.2.3. Because water recovery rate when using
high-recovery RO is increased from 85% to 95%, the reduced flowrates are labeled in Figure
A.2.4.

78
Figure A.2,2 𝑆𝐸𝐶 𝑁𝑒𝑡 with higher-salinity streams for the five seawater I&I scenarios when using CCRO with water-
recovery of 85% and 95%. The first two bars in each group represents the 𝑆𝐸𝐶 𝑁𝑒𝑡 for AWPFs without adding higher-
salinity streams. Every two bars are grouped together. The left bar and right bar represent the 𝑆𝐸𝐶 𝑁𝑒𝑡 for AWPFs with
water-recovery rate of 85% and 95%. The other eight bars in each group represent the 𝑆𝐸𝐶 𝑁𝑒𝑡 for AWPFs with
higher-salinity streams.

Figure A.2.3 Permeate (Figure A.2.3a) and brine (Figure A.2.3b) salinity without and with higher-salinity streams for
the five seawater I&I scenarios when using regular RO (with water-recovery of 85%) and high-recovery RO (with
water-recovery of 95%). The first two bars in each group represents the permeate salinity for AWPFs without adding
higher-salinity streams. Every two bars are grouped together. The left bar and right bar represent the permeate
79
salinity for AWPFs when using regular and high-recovery RO. The other eight bars in each group represent the
permeate salinity for AWPFs with higher-salinity streams.

Figure A.2.4 Schematic of flowrates and salinities for the wastewater, intruded seawater, and higher-salinity streams
entering an advanced water purification facility with high-recovery RO. The water recovery for high-recovery RO is set
to 95%. X represents the percentage of seawater I&I; a represents the salinity of the higher-salinity stream; b
represents the influent salinity to the advanced water purification facility; c and d represent the resulting salinities of
the RO permeate and brine. There are two possible blending points for the higher-salinity streams (points 1 and 2),
selection of which depends on the water quality of the higher-salinity stream. Because wastewater treatment
processes generally do not decrease salinity, the choice of blending point does not affect salinity values b, c, and d.

80
A.2.5 RO water-recovery rates for treated wastewater and higher-salinity streams for separate
desalination
Table A.2.3 RO water-recovery rates for treated wastewater and higher-salinity streams with lowest 𝑆𝐸𝐶 𝑁𝑒𝑡 when
desalinating higher-salinity streams separately from treated wastewater.
Seawater
I&I (%)
Higher-salinity stream type Water-recovery rate for
treated wastewater (%)
Water-recovery rate for
higher-salinity stream (%)
0 Regional brine interceptor 90 68
BWRO brine 1 90 68
BWRO brine 2 91 65
BWRO brine 3 93 58
2.5 Regional brine interceptor 88 75
BWRO brine 1 88 75
BWRO brine 2 89 72
BWRO brine 3 91 65
5 Regional brine interceptor 87 78
BWRO brine 1 87 78
BWRO brine 2 89 72
BWRO brine 3 90 68
7.5 Regional brine interceptor 86 82
BWRO brine 1 86 82
BWRO brine 2 88 75
BWRO brine 3 89 72
10 Regional brine interceptor 86 82
BWRO brine 1 86 82
BWRO brine 2 87 78
BWRO brine 3 89 72

81
A.2.5 Feed LSI when desalinating treated wastewater and higher-salinity streams together and
separately
Table A.2.4 Feed LSI when desalinating treated wastewater and higher-salinity streams and desalinating both
streams separately.
Seawater I&I
(%)
Higher-salinity stream type
LSI for treated
wastewater
LSI for higher-
salinity stream
LSI for blended
influent
0 Regional brine interceptor -0.59 0.32 -0.25
BWRO brine 1 -0.59 1.10 0.17
BWRO brine 2 -0.59 0.00 -0.24
BWRO brine 3 -0.59 0.58 -0.16
2.5 Regional brine interceptor -0.60 0.32 -0.25
BWRO brine 1 -0.60 1.10 0.16
BWRO brine 2 -0.60 0.00 -0.24
BWRO brine 3 -0.60 0.58 -0.15
5 Regional brine interceptor -0.58 0.32 -0.25
BWRO brine 1 -0.58 1.10 0.16
BWRO brine 2 -0.58 0.00 -0.24
BWRO brine 3 -0.58 0.58 -0.15
7.5 Regional brine interceptor -0.56 0.32 -0.24
BWRO brine 1 -0.56 1.10 0.16
BWRO brine 2 -0.56 0.00 -0.23
BWRO brine 3 -0.56 0.58 -0.14
10 Regional brine interceptor -0.54 0.32 -0.23
BWRO brine 1 -0.54 1.10
0.17
BWRO brine 2 -0.54 0.00
-0.23
BWRO brine 3 -0.54 0.58
-0.13

82
A.2.7 Water quality of treated wastewater, seawater and higher-salinity streams
Table A.2.5 Water quality of treated wastewater, seawater and higher-salinity streams
Water type Concentration (mg/L) pH
NH 4
+
K
+
Na
+
Mg
2+
Ca
2+
Sr
+
CO 3
2-
HCO 3
-
NO 3
-
Cl
-
F
-
SO 4
2-
PO 4
3-
SiO 2 B CO 2 TOC TDS
Treated
wastewater
20.1 0.0 213.0 23.0 77.0 0.0 1.2 272.0 4.0 219.0 1.1 254.0 2.1 21.9 0.0 8.1 10.5 1100 6.8
Seawater 0.0 380.0 10556.0 1262.0 400.0 13.0 6.7 132.6 0.0 18980.0 1.0 2649.0 0.0 0.8 4.8 1.7 0.0 34400 8.1
Regional
brine
interceptor
0.0 12.9 1182.3 192.4 528.0 4.2 0.6 170.5 0.0 2478.7 1.0 1022.4 0.0 51.4 0.0 13.2 14.7 5700 0.0
BWRO
brine 1
0.0 0.0 993.0 318.0 1035.1 0.0 1.8 575.8 0.0 2814.7 0.0 1548.4 0.0 115.7 0.0 45.8 14.7 7500 7.0
BWRO
brine 2
0.0 74.0 2140.7 400.9 1014.3 24.3 0.0 0.0 0.0 4554.9 5.7 2420.5 0.0 82.3 0.0 0.0 14.7 10900 7.0
BWRO
brine 3
0.0 0.0 5136.0 386.5 820.0 0.0 1.3 226.6 0.0 8949.5 0.0 1917.8 0.0 71.9 0.0 14.8 14.7 17500 7.0

83
A.2.8 Summary of permeate and brine salinities
Table A.2.6 Summary of permeate salinities with and without higher-salinity streams in influent
Percentage of SW
I&I
Without
higher-
salinity
stream
With
regional
brine
interceptor
as higher-
salinity
stream
With
BWRO
brine 1
as
higher-
salinity
stream
With
BWRO
brine 2
as
higher-
salinity
stream
With
BWRO
brine 3
as
higher-
salinity
stream
0% 4.1E+01 9.7E+01 1.2E+02 1.7E+02 3.6E+02
2.5% 9.2E+01 1.5E+02 1.7E+02 2.4E+02 4.3E+02
5% 1.6E+02 2.1E+02 2.3E+02 3.0E+02 5.0E+02
7.5% 2.4E+02 2.7E+02 3.0E+02 3.7E+02 5.8E+02
10% 3.3E+02 3.4E+02 3.7E+02 4.5E+02 6.6E+02

Table A.2.7 Summary of brine salinities with and without higher-salinity streams in influent
Percentage of SW
I&I
Without
higher-
salinity
stream
With
regional
brine
interceptor
as higher-
salinity
stream
With
BWRO
brine 1
as
higher-
salinity
stream
With
BWRO
brine 2
as
higher-
salinity
stream
With
BWRO
brine 3
as
higher-
salinity
stream
0% 6.9E+03 1.4E+04 1.6E+04 2.1E+04 3.0E+04
2.5% 1.2E+04 1.8E+04 2.0E+04 2.5E+04 3.4E+04
5% 1.7E+04 2.2E+04 2.4E+04 2.9E+04 3.8E+04
7.5% 2.2E+04 2.6E+04 2.8E+04 3.3E+04 4.2E+04
10% 2.8E+04 2.9E+04 3.2E+04 3.7E+04 4.6E+04

84

Figure A.2.5 Permeate (Figure A.2.5a) and brine (Figure A.2.5b) salinity without and with higher-salinity streams for
the five seawater I&I scenarios when using regular RO.

A.2.9 Model summary - Parameters and assumptions for WAVE software
The RO process was modeled using DOW
TM
WAVE design software.(DuPont Water
Solution, 2020) The RO membrane module modeled in this research was the BW30XFRLE-
400/34i module (DuPont Water Solutions, Edina, MN), which is suitable for both potable water
reuse and industrial water demineralization. The RO water-recovery was set to 85% based on
target system recoveries for large-scale AWPFs.(Bartels et al., 2005; DUPONT, 2021; Scott-
Roberts, 2016) The RO system was modeled to include 26 trains with each train having a two-
stage array. In stages 1 and 2, there are 88 and 34 vessels, respectively; each vessel contains
seven membrane elements.
The high-recovery RO process was modeled using DOW
TM
WAVE design
software.(DuPont Water Solution, 2020) The RO membrane module modeled in this research
was the FilmTec
TM
SOAR-4000 (DuPont Water Solutions, Edina, MN. The high-recovery RO
water-recovery was set to 85% based on the system recoveries for large-scale AWPFs.(Bartels
et al., 2005; DUPONT, 2021; Scott-Roberts, 2016) The high-recovery RO system was modeled
to include 26 trains with each train having a one-stage array. There are 122 vessels in each
stage; each vessel contains seven membrane elements.

85
The Water quality of treated wastewater, seawater and higher-salinity streams were
summarized in Table A.2.5. The pump efficiency (for both high pressure pump and interstage
booster pump) and motor efficiency were set to 0.84 and 0.95, and the total efficiency is 0.798.
The flow factor (accounting for flow loss due to fouling) was 0.85 and the temperature is 25
o
C in
this study.

86
A.3 Supplementary Information to Chapter 4
A.3.1 Summary of comparisons between 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛
, 𝑆𝐸𝐶 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑖𝑛 , and 𝑆𝐸𝐶 𝐻𝑅𝑅𝑂 ,𝑚𝑖𝑛
According to Equation (4.2) and (4.5) (Wenten and Khoiruddin, 2016),
𝑆𝐸𝐶 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑖𝑛 : 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛
= 𝑇𝐸𝐸 𝑅𝑂 ,𝑚𝑎𝑥 : 𝑇𝐸𝐸 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑎𝑥 = (1 − 𝑊𝑅 )ln (
1
1−𝑊𝑅
) ∶
1−𝑊𝑅
𝑊𝑅
ln (
1
1−𝑊𝑅
) = 𝑊𝑅
𝑆𝐸𝐶 𝐶𝐶𝑅𝑂 ,𝑚𝑖𝑛 : 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛
= 𝑇𝐸𝐸 𝑅𝑂 ,𝑚𝑎𝑥 : 𝑇𝐸𝐸 𝐶𝐶𝑅𝑂 ,𝑚𝑎𝑥 = (1 − 𝑊𝑅 )ln (
1
1−𝑊𝑅
) ∶ ln (
1
1−𝑊𝑅
)
4
(
4
4−𝑊𝑅
+
2
2−𝑊𝑅
+
4
4−3𝑊𝑅
+
1
1−𝑊𝑅
)
.
In Table A.3.1, values for 𝑆𝐸𝐶 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑖𝑛 : 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛
, and 𝑆𝐸𝐶 𝐶𝐶𝑅𝑂 ,𝑚𝑖𝑛 : 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛
according to 𝑊𝑅 are shown.
Table A.3.1 Summary of comparisons between 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛
, 𝑆𝐸𝐶 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑖𝑛 , and 𝑆𝐸𝐶 𝐶𝐶𝑅𝑂 ,𝑚𝑖𝑛
𝑊𝑅 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95%
𝑆𝐸𝐶 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑖𝑛 : 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛
5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95%
𝑆𝐸𝐶 𝐶𝐶𝑅𝑂 ,𝑚𝑖𝑛 : 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛
98% 96% 94% 92% 90% 87% 85% 82% 79% 76% 73% 69% 65% 61% 57% 52% 47% 40% 33%
1 − 𝑆𝐸𝐶 𝑅𝑂 −𝐸𝑅𝐷 ,𝑚𝑖𝑛 : 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛
95% 90% 85% 80% 75% 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5%
1 − 𝑆𝐸𝐶 𝐶𝐶𝑅𝑂 ,𝑚𝑖𝑛 : 𝑆𝐸𝐶 𝑅𝑂 ,𝑚𝑖𝑛
2% 4% 6% 8% 10% 13% 15% 18% 21% 24% 27% 31% 35% 39% 43% 48% 53% 60% 67%

87
References
Achilli, A. and Childress, A.E. 2010. Pressure retarded osmosis: From the vision of Sidney Loeb to the
first prototype installation - Review. Desalination 261(3), 205-211.
Achilli, A., Prante, J.L., Hancock, N.T., Maxwell, E.B. and Childress, A.E. 2014. Experimental Results
from RO-PRO: A Next Generation System for Low-Energy Desalination. Environmental Science
& Technology 48(11), 6437-6443.
Al-Obaidi, M., Kara-Zaitri, C. and Mujtaba, I.M. 2020. Wastewater Treatment by Reverse Osmosis
Process: State of the Art & Process Modelling. CRC Press.
Alghoul, M.A., Poovanaesvaran, P., Sopian, K. and Sulaiman, M.Y. 2009. Review of brackish water
reverse osmosis (BWRO) system designs. Renewable & Sustainable Energy Reviews 13(9),
2661-2667.
Alhumoud, J.M., Alhumaidi, H.M., Al-Ghusain, I.N. and Alhumoud, A.M. 2010. Cost/Benefit Evaluation
Of Sulaibiya Wastewater Treatment Plant In Kuwait. International Business & Economics
Research Journal (IBER) 9(2).
Alnouri, S.Y. and Linke, P. 2014. Optimal seawater reverse osmosis network design considering product
Water boron specifications. Desalination 345, 112-127.
Altaee, A. and Hilal, N. 2015. High recovery rate NF-FO-RO hybrid system for inland brackish water
treatment. Desalination 363, 19-25.
Alturki, A.A., Tadkaew, N., McDonald, J.A., Khan, S.J., Price, W.E. and Nghiem, L.D. 2010. Combining
MBR and NF/RO membrane filtration for the removal of trace organics in indirect potable water
reuse applications. Journal of Membrane Science 365(1-2), 206-215.
Amy, G., Ghaffour, N., Li, Z.Y., Francis, L., Linares, R.V., Missimer, T. and Lattemann, S. 2017.
Membrane-based seawater desalination: Present and future prospects. Desalination 401, 16-21.
Antony, A., Low, J.H., Gray, S., Childress, A.E., Le-Clech, P. and Leslie, G. 2011. Scale formation and
control in high pressure membrane water treatment systems: A review. Journal of Membrane
Science 383(1-2), 1-16.
Atkinson, S. 2020. Wastewater treatment facilities in the USA and Europe employ SUEZ's MBR, UF and
RO technologies. Membrane Technology 2020(1), 5-7.
Bartels, C.R., Wilf, M., Andes, K. and Iong, J. 2005. Design considerations for wastewater treatment by
reverse osmosis. Water Science and Technology 51(6-7), 473-482.
Befus, K.M., Barnard, P.L., Hoover, D.J., Hart, J.A.F. and Voss, C.I. 2020. Increasing threat of coastal
groundwater hazards from sea-level rise in California. Nature Climate Change 10(10), 946-+.
Binger, Z.M. and Achilli, A. 2020. Forward osmosis and pressure retarded osmosis process modeling for
integration with seawater reverse osmosis desalination. Desalination 491.
Bluefield Research 2015. U.S. Municipal Wastewater & Reuse: Market Trends, Opportunities and
Forecasts, 2015-2025. Insight Reports Water Reuse.
California Environmental Protection Agency 2019. Amendment to California ocean plan.
Available: https://www.waterboards.ca.gov/water_issues/programs/ocean/docs/oceanplan2019.p
df
California State Water Resources Control Board 2018. Title 22 code of regulations.
Available: https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/documents/lawbo
ok/rwregulations_20181001a.pdf. Regulations Related to Recycled Water.
Carlsbad Municipal Water District 2012. Phase III recycled water project feasibility study. Available:
http://www.bidnet.com/bneattachments?/341804554.pdf.
Cath, T.Y., Childress, A.E. and Elimelech, M. 2006. Forward osmosis: Principles, applications, and
recent developments. Journal of Membrane Science 281(1-2), 70-87.
Cath, T.Y., Gormly, S., Beaudry, E.G., Flynn, M.T., Adams, V.D. and Childress, A.E. 2005. Membrane
contactor processes for wastewater reclamation in space Part I. Direct osmotic concentration as
pretreatment for reverse osmosis. Journal of Membrane Science 257(1-2), 85-98.
Cath, T.Y., Hancock, N.T., Lundin, C.D., Hoppe-Jones, C. and Drewes, J.E. 2010. A multi-barrier
osmotic dilution process for simultaneous desalination and purification of impaired water. Journal
of Membrane Science 362(1-2), 417-426.

88
Chew, M.Y.C., Watanabe, C. and Tou, Y. 2011. The challenges in Singapore NEWater development:
Co-evolutionary development for innovation and industry evolution. Technology in Society 33(3-
4), 200-211.
Chuang, Y.H. and Mitch, W.A. 2017. Effect of Ozonation and Biological Activated Carbon Treatment of
Wastewater Effluents on Formation of N-nitrosamines and Halogenated Disinfection Byproducts.
Environmental Science & Technology 51(4), 2329-2338.
Chuang, Y.H., Szczuka, A., Shabani, F., Munoz, J., Aflaki, R., Hammond, S.D. and Mitch, W.A. 2019.
Pilot-scale comparison of microfiltration/reverse osmosis and ozone/biological activated carbon
with UV/hydrogen peroxide or UV/free chlorine AOP treatment for controlling disinfection
byproducts during wastewater reuse. Water Research 152, 215-225.
Cordoba, S., Das, A., Leon, J., Garcia, J.M. and Warsinger, D.M. 2021. Double-acting batch reverse
osmosis configuration for best-in-class efficiency and low downtime. Desalination 506, 114959.
Donose, B.C., Sukumar, S., Pidou, M., Poussade, Y., Keller, J. and Gernjak, W. 2013. Effect of pH on
the ageing of reverse osmosis membranes upon exposure to hypochlorite. Desalination 309, 97-
105.
Dow Chemical Company 2019. Dow chemical Company’s DOW™ WAVE design software - version 1.6.
Available: https://www.dupont.com/water/design-software.html
Drak, A. and Adato, M. 2014. Energy recovery consideration in brackish water desalination. Desalination
339, 34-39.
Du, Y.W., Liu, Y., Zhang, S.F. and Xu, Y.J. 2016. Optimization of Seawater Reverse Osmosis
Desalination Networks with Permeate Split Design Considering Boron Removal. Industrial &
Engineering Chemistry Research 55(50), 12860-12879.
Du, Y.W., Xie, L.X., Liu, Y., Zhang, S.F. and Xu, Y.J. 2015. Optimization of reverse osmosis networks
with split partial second pass design. Desalination 365, 365-380.
DUPONT 2021. FILMTEC Membranes Reclaim Waste Water at 86% Recovery in Singapore.
Available: https://www.dupont.com/content/dam/dupont/amer/us/en/water-
solutions/public/documents/en/45-D01522-en.pdf. Customer Success Story.
DuPont Water Solution 2020. DOW
TM
WAVE design software. Available:
https://www.dupont.com/water/resources/design-software.html.
DuPont Water Solutions 2021. Desalitech Closed Circuit Reverse Osmosis.
Available: https://www.dupont.com/brands/desalitech.html.
Efraty, A. 2010a. US Patent No 7,628,921.
Efraty, A. 2010b. US Patent No 7,695,614.
Elimelech, M. and Phillip, W.A. 2011. The Future of Seawater Desalination: Energy, Technology, and
the Environment. Science 333(6043), 712-717.
Energy Recovery Inc 2019. Energy recovery’s power model.
Available: http://www.energyrecovery.com/resource/power-model/
Fard, A.K., Rhadfi, T., Khraisheh, M., Atieh, M.A. and Hilal, N. 2016. Reducing flux decline and fouling of
direct contact membrane distillation by utilizing thermal brine from MSF desalination plant.
Desalination 379, 172-181.
Gerrity, D., Pecson, B., Trussell, R.S. and Trussell, R.R. 2013. Potable reuse treatment trains
throughout the world. Journal of Water Supply Research and Technology-Aqua 62(6), 321-338.
Gerrity, D., Pisarenko, A.N., Marti, E., Trenholm, R.A., Gerringer, F., Reungoat, J. and Dickenson, E.
2015. Nitrosamines in pilot-scale and full-scale wastewater treatment plants with ozonation.
Water Research 72, 251-261.
Global Water Intelligence (GWI) 2021. DesalData database. Available: https://www.desaldata.com/.
Greenlee, L.F., Lawler, D.F., Freeman, B.D., Marrot, B. and Moulin, P. 2009. Reverse osmosis
desalination: Water sources, technology, and today's challenges. Water Research 43(9), 2317-
2348.
Greve, P., Kahil, T., Mochizuki, J., Schinko, T., Satoh, Y., Burek, P., Fischer, G., Tramberend, S.,
Burtscher, R., Langan, S. and Wada, Y. 2018. Global assessment of water challenges under
uncertainty in water scarcity projections. Nature Sustainability 1(9), 486-494.
Gude, V.G. 2017. Desalination and water reuse to address global water scarcity. Reviews in
Environmental Science and Bio-Technology 16(4), 591-609.

89
Hamoda, M.F., Attia, N.F. and Al-Ghusain, I.A. 2015. Performance evaluation of a wastewater
reclamation plant using ultrafiltration and reverse osmosis. Desalination and Water Treatment
54(11), 2928-2938.
Han, G., Zhang, S., Li, X. and Chung, T.S. 2013. High performance thin film composite pressure
retarded osmosis (PRO) membranes for renewable salinity-gradient energy generation. Journal
of Membrane Science 440, 108-121.
Hancock, N.T., Black, N.D. and Cath, T.Y. 2012. A comparative life cycle assessment of hybrid osmotic
dilution desalination and established seawater desalination and wastewater reclamation
processes. Water Research 46(4), 1145-1154.
Hancock, N.T., Xu, P., Heil, D.M., Bellona, C. and Cath, T.Y. 2011. Comprehensive Bench- and Pilot-
Scale Investigation of Trace Organic Compounds Rejection by Forward Osmosis. Environmental
Science & Technology 45(19), 8483-8490.
Hancock, N.T., Xu, P., Roby, M.J., Gomez, J.D. and Cath, T.Y. 2013. Towards direct potable reuse with
forward osmosis: Technical assessment of long-term process performance at the pilot scale.
Journal of Membrane Science 445, 34-46.
Henthome, L. and Boysen, B. 2015. State-of-the-art of reverse osmosis desalination pretreatment.
Desalination 356, 129-139.
Holloway, R.W., Miller-Robbie, L., Patel, M., Stokes, J.R., Munakata-Marr, J., Dadakis, J. and Cath, T.Y.
2016. Life-cycle assessment of two potable water reuse technologies: MF/RO/UV-AOP treatment
and hybrid osmotic membrane bioreactors. Journal of Membrane Science 507, 165-178.
Hummel, M.A., Berry, M.S. and Stacey, M.T. 2018. Sea Level Rise Impacts on Wastewater Treatment
Systems Along the US Coasts. Earths Future 6(4), 622-633.
International Water Association 2020. City water stories: Singapore. Available: https://iwa-
network.org/city/singapore/.
Jang, E.S., Mickols, W., Sujanani, R., Helenic, A., Dilenschneider, T.J., Kamcev, J., Paul, D.R. and
Freeman, B.D. 2019. Influence of concentration polarization and thermodynamic non-ideality on
salt transport in reverse osmosis membranes. Journal of Membrane Science 572, 668-675.
Jenkins, S., Paduan, J., Roberts, P.J.W., Schlenk, D. and Weis, J. 2012. Management of Brine
Discharges to Coastal Waters Recommendations of a Science Advisory Panel. Southern
California coastal water research project. Costa Mesa, CA.
Jeon, J., Kwak, K., Kim, N., Jung, J., Son, D.M. and Kim, S. 2017. Study on the Necessity of Energy
Recovery Device in Small Scale Reverse Osmosis Desalination Plant. Korean Chemical
Engineering Research 55(6), 762-766.
Ji, X., Curcio, E., Al Obaidani, S., Di Profio, G., Fontananova, E. and Drioli, E. 2010. Membrane
distillation-crystallization of seawater reverse osmosis brines. Separation and Purification
Technology 71(1), 76-82.
Jiang, S.X., Li, Y.N. and Ladewig, B.P. 2017. A review of reverse osmosis membrane fouling and control
strategies. Science of the Total Environment 595, 567-583.
Jin, P., Jin, X., Wang, X., Feng, Y. and Wang, X.C. 2013. Biological activated carbon treatment process
for advanced water and wastewater treatment. Biomass Now-Cultivation and Utilization, 153-192.
Jones, E., Qadir, M., van Vliet, M.T.H., Smakhtin, V. and Kang, S.M. 2019. The state of desalination and
brine production: A global outlook. Science of the Total Environment 657, 1343-1356.
Jones, E. and van Vliet, M.T.H. 2018. Drought impacts on river salinity in the southern US: Implications
for water scarcity. Science of the Total Environment 644, 844-853.
Kadaj, E. and Bosleman, R. 2018. Energy recovery devices in membrane desalination processes.
Renewable Energy Powered Desalination Handbook, 415-444.
Kamcev, J., Paul, D.R., Manning, G.S. and Freeman, B.D. 2017. Accounting for frame of reference and
thermodynamic non-idealities when calculating salt diffusion coefficients in ion exchange
membranes. Journal of Membrane Science 537, 396-406.
Kenigsberg, C., Abramovich, S. and Hyams-Kaphzan, O. 2020. The effect of long-term brine discharge
from desalination plants on benthic foraminifera. Plos One 15(1).
Kim, J. and Hong, S. 2018. A novel single-pass reverse osmosis configuration for high-purity water
production and low energy consumption in seawater desalination. Desalination 429, 142-154.
Kim, J., Park, K. and Hong, S. 2020. Optimization of two-stage seawater reverse osmosis membrane
processes with practical design aspects for improving energy efficiency. Journal of Membrane
Science 601, 11.

90
Kim, Y., Elimelech, M., Shon, H.K. and Hong, S. 2014. Combined organic and colloidal fouling in forward
osmosis: Fouling reversibility and the role of applied pressure. Journal of Membrane Science 460,
206-212.
Kimura, K., Amy, G., Drewes, J.E., Heberer, T., Kim, T.U. and Watanabe, Y. 2003. Rejection of organic
micropollutants (disinfection by-products, endocrine disrupting compounds, and pharmaceutically
active compounds) by NF/RO membranes. Journal of Membrane Science 227(1-2), 113-121.
King County Department of Natural Resources and Parks 2011. Saltwater intrusion and infiltration into
the King County wastewater system. Available:
https://your.kingcounty.gov/dnrp/library/wastewater/cso/docs/2011-
03_SaltwaterIntrusionAndInfiltrationStudy.pdf.
Krayer, S.A., Michaels, I.M. and Solomon, P.T. 2017. Salinity Impacts on Coastal Wastewater Treatment
Facilities. A Major Qualifying Project Report - Degree of Bachelor of Science.
Kurihara, M. and Hanakawa, M. 2013. Mega-ton Water System: Japanese national research and
development project on seawater desalination and wastewater reclamation. Desalination 308,
131-137.
Langelier, W.F. 1936. The Analytical Control of Anti-Corrosion Water Treatment. Journal American
Water Works Association 28(10), 1500-1521.
Lazarova, V., Sheilds, P., Levine, B., Savoye, P., Hranisavljevic, D., Renaud, P. and Iwa Programme, C.
2003. Production of high quality water for reuse purposes: the West Basin experience. 3rd World
Water Congress: Efficient Water Supply and Water Reuse 3(3), 167-175.
Lee, H.J., Halali, M.A., Baker, T., Sarathy, S. and de Lannoy, C.F. 2020. A comparative study of RO
membrane scale inhibitors in wastewater reclamation: Antiscalants versus pH adjustment.
Separation and Purification Technology 240.
Lee, S., Boo, C., Elimelech, M. and Hong, S. 2010. Comparison of fouling behavior in forward osmosis
(FO) and reverse osmosis (RO). Journal of Membrane Science 365(1-2), 34-39.
Lee, S., Kim, Y., Kim, A.S. and Hong, S. 2016. Evaluation of membrane-based desalting processes for
RO brine treatment. Desalination and Water Treatment 57(16), 7432-7439.
Leusch, F.D.L. and Snyder, S.A. 2015. Bioanalytical tools: half a century of application for potable reuse.
Environmental Science-Water Research & Technology 1(5), 606-621.
Leverenz, H.L., Tchobanoglous, G. and Asano, T. 2011. Direct potable reuse: a future imperative.
Journal of Water Reuse and Desalination 1(1), 2-10.
Li, M.H. 2010. Minimization of Energy in Reverse Osmosis Water Desalination Using Constrained
Nonlinear Optimization. Industrial & Engineering Chemistry Research 49(4), 1822-1831.
Li, M.H. 2012. Optimal plant operation of brackish water reverse osmosis (BWRO) desalination.
Desalination 293, 61-68.
Lin, S.H. 2020. Energy Efficiency of Desalination: Fundamental Insights from Intuitive Interpretation.
Environmental Science & Technology 54(1), 76-84.
Lin, S.H. and Elimelech, M. 2015. Staged reverse osmosis operation: Configurations, energy efficiency,
and application potential. Desalination 366, 9-14.
Linares, R.V., Li, Z., Yangali-Quintanilla, V., Ghaffour, N., Amy, G., Leiknes, T. and Vrouwenvelder, J.S.
2016. Life cycle cost of a hybrid forward osmosis low pressure reverse osmosis system for
seawater desalination and wastewater recovery. Water Research 88, 225-234.
Liu, N., Liu, Z.L., Li, Y.X. and Sang, L.X. 2016. Development and experimental studies on a fully-rotary
valve energy recovery device for SWRO desalination system. Desalination 397, 67-74.
Lively, R.P. and Sholl, D.S. 2017. From water to organics in membrane separations. Nature Materials
16(3), 276-279.
Lozier, J. and Ortega, K. 2010. The Oxnard advanced water purification facility: combining indirect
potable reuse with reverse osmosis concentrate beneficial use to ensure a California community's
water sustainability and provide coastal wetlands restoration. Water Science and Technology
61(5), 1157-1163.
Lyu, S.D., Chen, W.P., Zhang, W.L., Fan, Y.P. and Jiao, W.T. 2016. Wastewater reclamation and reuse
in China: Opportunities and challenges. Journal of Environmental Sciences 39, 86-96.
Martinetti, C.R., Childress, A.E. and Cath, T.Y. 2009. High recovery of concentrated RO brines using
forward osmosis and membrane distillation. Journal of Membrane Science 331(1-2), 31-39.

91
McCurry, D.L., Ishida, K.P., Oelker, G.L. and Mitch, W.A. 2017. Reverse Osmosis Shifts Chloramine
Speciation Causing Re-Formation of NDMA during Potable Reuse of Wastewater. Environmental
Science & Technology 51(15), 8589-8596.
Mekonnen, M.M. and Hoekstra, A.Y. 2016. Four billion people facing severe water scarcity. Science
Advances 2(2).
Meridian Institute and Paradigm Environmental 2018. Mainstreaming potable water reuse in the United
States: strategies for leveling the playing field.
Available: https://www.epa.gov/sites/production/files/2018-
04/documents/mainstreaming_potable_water_reuse_april_2018_final_for_web.pdf.
Missimer, T.M., Ghaffour, N., Dehwah, A.H.A., Rachman, R., Maliva, R.G. and Amy, G. 2013.
Subsurface intakes for seawater reverse osmosis facilities: Capacity limitation, water quality
improvement, and economics. Desalination 322, 37-51.
Missimer, T.M. and Maliva, R.G. 2018. Environmental issues in seawater reverse osmosis desalination:
Intakes and outfalls. Desalination 434, 198-215.
Mistry, K.H., McGovern, R.K., Thiel, G.P., Summers, E.K., Zubair, S.M. and Lienhard, J.H. 2011.
Entropy Generation Analysis of Desalination Technologies. Entropy 13(10), 1829-1864.
Mitrouli, S., Karabelas, A.J., Karanasiou, A. and Kostoglou, M. 2013. Incipient calcium carbonate scaling
of desalination membranes in narrow channels with spacers-experimental insights. Journal of
Membrane Science 425, 48-57.
Murad, S. and Powles, J.G. 1993. A COMPUTER-SIMULATION OF THE CLASSIC EXPERIMENT ON
OSMOSIS AND OSMOTIC-PRESSURE. Journal of Chemical Physics 99(9), 7271-7272.
National Water Research Institute 2018. Guidance Framework for Direct Potable Reuse in Arizona.
Ng, K.C., Thu, K., Oh, S.J., Ang, L., Shahzad, M.W. and Bin Ismail, A. 2015. Recent developments in
thermally-driven seawater desalination: Energy efficiency improvement by hybridization of the
MED and AD cycles. Desalination 356, 255-270.
Nix, D.K., Southard, M., Burris, H., Adams, H. and Schreiber, R. 2021. Tracking Wichita Falls' Path from
DPR to IPR. Opflow 47(2), 10-15.
O'Toole, G., Jones, L., Coutinho, C., Hayes, C., Napoles, M. and Achilli, A. 2016. River-to-sea pressure
retarded osmosis: Resource utilization in a full-scale facility. Desalination 389, 39-51.
Ocean Health 2020. Detailed composition of seawater at 3.5% salinity. Available:
https://oceanplasma.org/documents/chemistry.html.
Oren, Y., Korngold, E., Daltrophe, N., Messalem, R., Volkman, Y., Aronov, L., Weismann, M., Bouriakov,
N., Glueckstern, P. and Gilron, J. 2010. Pilot studies on high recovery BWRO-EDR for near zero
liquid discharge approach. Desalination 261(3), 321-330.
Owens, E., Davis, E. and Hosseini, T. 2014. Desalting Southern California: Comparing Seven Utilities'
Experiences. Opflow 40(11), 16-20.
Pan, S.Y., Haddad, A.Z., Kumar, A. and Wang, S.W. 2020. Brackish water desalination using reverse
osmosis and capacitive deionization at the water-energy nexus. Water Research 183, 23.
Panagopoulos, A., Haralambous, K.J. and Loizidou, M. 2019. Desalination brine disposal methods and
treatment technologies - A review. Science of the Total Environment 693, 23.
Park, K., Kim, J., Yang, D.R. and Hong, S. 2020. Towards a low-energy seawater reverse osmosis
desalination plant: A review and theoretical analysis for future directions. Journal of Membrane
Science 595.
Park, P.K., Lee, S., Cho, J.S. and Kim, J.H. 2012. Full-scale simulation of seawater reverse osmosis
desalination processes for boron removal: Effect of membrane fouling. Water Research 46(12),
3796-3804.
Pecson, B., Trussell, S., Chen, E., Kaufmann, A. and Trussell, R. 2020. Considerations for Direct
Potable Reuse Downstream of the Groundwater
Recharge Advanced Water Treatment Facility.
Available: http://www.mwdh2o.com/DocSvcsPubs/rrwp/assets/final-dpr-awtf-tech-memo.pdf.
Pecson, B.M., Triolo, S.C., Olivieri, S., Chen, E.C., Pisarenko, A.N., Yang, C.C., Olivieri, A., Haas, C.N.,
Trussell, R.S. and Trussell, R.R. 2017. Reliability of pathogen control in direct potable reuse:
Performance evaluation and QMRA of a full-scale 1 MGD advanced treatment train. Water
Research 122, 258-268.

92
Penate, B. and Garcia-Rodriguez, L. 2011. Energy optimisation of existing SWRO (seawater reverse
osmosis) plants with ERT (energy recovery turbines): Technical and thermoeconomic
assessment. Energy 36(1), 613-626.
Plata, S.L. and Childress, A.E. 2019. Limiting power density in pressure-retarded osmosis: Observation
and implications. Desalination 467, 51-56.
Pramanik, B.K., Shu, L. and Jegatheesan, V. 2017. A review of the management and treatment of brine
solutions. Environmental Science-Water Research & Technology 3(4), 625-658.
Prante, J.L., Ruskowitz, J.A., Childress, A.E. and Achilli, A. 2014. RO-PRO desalination: An integrated
low-energy approach to seawater desalination. Applied Energy 120, 104-114.
Radcliffe, J.C. and Page, D. 2020. Water reuse and recycling in Australia-history, current situation and
future perspectives. Water Cycle (1), 19-40.
Regional Recycled Water Advanced Purification Center 2021. A new source of water for Southern
California. Available: http://www.mwdh2o.com/DocSvcsPubs/rrwp/index.html#home.
Rodriguez, C., Van Buynder, P., Lugg, R., Blair, P., Devine, B., Cook, A. and Weinstein, P. 2009.
Indirect Potable Reuse: A Sustainable Water Supply Alternative. International Journal of
Environmental Research and Public Health 6(3), 1174-1209.
Santa Ana Watershed Project Authority (SAWPA) 2021. Brine Line Mapping Tools. Available from:
https://www.sawpa.net/sari/sari.htm.
Sardari, K., Fyfe, P., Lincicome, D. and Wickramasinghe, S.R. 2018. Combined electrocoagulation and
membrane distillation for treating high salinity produced waters. Journal of Membrane Science
564, 82-96.
Sassi, K.M. and Mujtaba, I.M. 2013. MINLP based superstructure optimization for boron removal during
desalination by reverse osmosis. Journal of Membrane Science 440, 29-39.
Schwabe, K., Nemati, M., Amin, R., Tran, Q. and Jassby, D. 2020. Unintended consequences of water
conservation on the use of treated municipal wastewater. Nature Sustainability 3(8), 628-635.
Scott-Roberts, S. 2016. Engineer’s report for the groundwater replenishment system final expansion
projects. Available from: https://www.ocwd.com/media/5234/gwrs-fe-engineers-report-
complete.pdf.
Shaffer, D.L., Yip, N.Y., Gilron, J. and Elimelech, M. 2012. Seawater desalination for agriculture by
integrated forward and reverse osmosis: Improved product water quality for potentially less
energy. Journal of Membrane Science 415, 1-8.
Sharqawy, M.H., Zubair, S.M. and Lienhard, J.H. 2011. Second law analysis of reverse osmosis
desalination plants: An alternative design using pressure retarded osmosis. Energy 36(11), 6617-
6626.
She, Q.H., Jin, X. and Tang, C.Y.Y. 2012. Osmotic power production from salinity gradient resource by
pressure retarded osmosis: Effects of operating conditions and reverse solute diffusion. Journal
of Membrane Science 401, 262-273.
Shultz, S. and Freger, V. 2018. In situ modification of membrane elements for improved boron rejection
in RO desalination. Desalination 431, 66-72.
Singapore National Water Agency 2021a. Desalinated water.
Available: https://www.pub.gov.sg/watersupply/fournationaltaps/desalinatedwater.
Singapore National Water Agency 2021b. NEWater. Available
at: https://www.pub.gov.sg/watersupply/fournationaltaps/newater.
Soller, J.A., Eftim, S.E. and Nappier, S.P. 2019. Comparison of Predicted Microbiological Human Health
Risks Associated with de Facto, Indirect, and Direct Potable Water Reuse. Environmental
Science & Technology 53(22), 13382-13389.
Srinivasamoorthy, K., Vasanthavigar, M., Chidambaram, S., Anandhan, P. and Sarma, V.S. 2011.
Characterisation of groundwater chemistry in an eastern coastal area of Cuddalore district, Tamil
Nadu. Journal of the Geological Society of India 78(6), 549-558.
State Water Resources Control Board 2019. Water quality control plan for ocean waters of California
(Ocean Plan).
Available: https://www.waterboards.ca.gov/water_issues/programs/ocean/docs/oceanplan2019.p
df.
Stein, S., Russak, A., Sivan, O., Yechieli, Y., Rahav, E., Oren, Y. and Kasher, R. 2016. Saline
Groundwater from Coastal Aquifers As a Source for Desalination. Environmental Science &
Technology 50(4), 1955-1963.

93
Stover, R.L. 2013. Industrial and brackish water treatment with closed circuit reverse osmosis.
Desalination and Water Treatment 51(4-6), 1124-1130.
Stover, R.L. 2016. High recovery, low fouling, and low energy reverse osmosis. Desalination and Water
Treatment 57(55), 26501-26506.
Straub, A.P., Yip, N.Y. and Elimelech, M. 2014. Raising the Bar: Increased Hydraulic Pressure Allows
Unprecedented High Power Densities in Pressure-Retarded Osmosis. Environmental Science &
Technology Letters 1(1), 55-59.
Tang, C.Y., Yang, Z., Guo, H., Wen, J.J., Nghiem, L.D. and Cornelissen, E. 2018. Potable Water Reuse
through Advanced Membrane Technology. Environmental Science & Technology 52(18), 10215-
10223.
Tang, F., Hu, H.Y., Sun, L.J., Sun, Y.X., Shi, N. and Crittenden, J.C. 2016. Fouling characteristics of
reverse osmosis membranes at different positions of a full-scale plant for municipal wastewater
reclamation. Water Research 90, 329-336.
Tang, F., Hu, H.Y., Sun, L.J., Wu, Q.Y., Jiang, Y.M., Guan, Y.T. and Huang, J.J. 2014. Fouling of
reverse osmosis membrane for municipal wastewater reclamation: Autopsy results from a full-
scale plant. Desalination 349, 73-79.
Tchobanoglous, G., Cotruvo, J., Crook, J., McDonald, E., Olivieri, A., Salveson, A. and Trussell, R.S.
2015. Framework for direct potable reuse. WateReuse Research Foundation.
Tenne, A., Hoffman, D. and Levi, E. 2013. Quantifying the actual benefits of large-scale seawater
desalination in Israel. Desalination and Water Treatment 51(1-3), 26-37.
Tularam, G.A. and Ilahee, M. 2007. Environmental concerns of desalinating seawater using reverse
osmosis. Journal of Environmental Monitoring 9(8), 805-813.
US Environmental Protection (US EPA) 2018. Potable reuse compendium.
Available: https://www.epa.gov/sites/production/files/2018-
01/documents/potablereusecompendium_3.pdf?TB_iframe=true&width=370.8&height=658.8.
US Environmental Protection (US EPA) 2020. Improving the security, sustainability, and resilience of
our nation’s water resources. Available: https://www.epa.gov/sites/production/files/2020-
02/documents/national-water-reuse-action-plan-collaborative-implementation-version-1.pdf.
National Water Reuse Action Plan.
US Environmental Protection Agency (US EPA) 2019. Water infrastructure finance and innovation act –
Pure Water Monterey Groundwater Replenishment Project.
Available: https://www.epa.gov/sites/production/files/2019-
10/documents/monterey_one_water_0.pdf.
Van't Hoff, J. 1888. XII. The function of osmotic pressure in the analogy between solutions and gases.
The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science 26(159), 81-
105.
Veldkamp, T.I.E., Wada, Y., Aerts, J., Doll, P., Gosling, S.N., Liu, J., Masaki, Y., Oki, T., Ostberg, S.,
Pokhrel, Y., Satoh, Y., Kim, H. and Ward, P.J. 2017. Water scarcity hotspots travel downstream
due to human interventions in the 20th and 21st century. Nature Communications 8, 12.
Venkatesan, A.K., Ahmad, S., Johnson, W. and Batista, J.R. 2011. Systems dynamic model to forecast
salinity load to the Colorado River due to urbanization within the Las Vegas Valley. Science of the
Total Environment 409(13), 2616-2625.
Voutchkov, N. 2011. Overview of seawater concentrate disposal alternatives. Desalination 273(1), 205-
219.
Voutchkov, N. 2018a. Energy use for membrane seawater desalination - current status and trends.
Desalination 431, 2-14.
Voutchkov, N. 2018b. Membrane Desalination—Process Selection, Design, and Implementation.
Sustainable Desalination Handbook, 3-24.
Walker, W.S. 2010. Improving Recovery in Reverse Osmosis Desalination of Inland Brackish
Groundwaters via Electrodialysis. Available: https://repositories.lib.utexas.edu/handle/2152/ETD-
UT-2010-08-1693. Doctoral dissertation at the University of Austin at Texas.
Warsinger, D.M., Chakraborty, S., Tow, E.W., Plumlee, M.H., Bellona, C., Loutatidou, S., Karimi, L.,
Mikelonis, A.M., Achilli, A., Ghassemi, A., Padhye, L.P., Snyder, S.A., Curcio, S., Vecitis, C.D.,
Arafat, H.A. and Lienhard, V.J.H. 2018. A review of polymeric membranes and processes for
potable water reuse. Progress in Polymer Science 81, 209-237.

94
Warsinger, D.M., Tow, E.W., Nayar, K.G., Maswadeh, L.A. and Lienhard, J.H. 2016. Energy efficiency of
batch and semi-batch (CCRO) reverse osmosis desalination. Water Research 106, 272-282.
WateReuse Project 2015. Role of Retention Time in the Environmental Buffer of Indirect Potable Reuse
Projects: An Investigation on Managed Aquifer Recharge.
Available: https://watereuse.org/watereuse-research/role-of-retention-time-in-the-environmental-
buffer-of-indirect-potable-reuse-projects-an-investigation-on-managed-aquifer-recharge/.
Wei, X., Binger, Z.M., Achilli, A., Sanders, K.T. and Childress, A.E. 2020. A modeling framework to
evaluate blending of seawater and treated wastewater streams for synergistic desalination and
potable reuse. Water Research 170, 11.
Wenten, I.G. and Khoiruddin 2016. Reverse osmosis applications: Prospect and challenges.
Desalination 391, 112-125.
Werber, J.R., Deshmukh, A. and Elimelech, M. 2017. Can batch or semi-batch processes save energy in
reverse-osmosis desalination? Desalination 402, 109-122.
Werner, A.D., Bakker, M., Post, V.E.A., Vandenbohede, A., Lu, C.H., Ataie-Ashtiani, B., Simmons, C.T.
and Barry, D.A. 2013. Seawater intrusion processes, investigation and management: Recent
advances and future challenges. Advances in Water Resources 51, 3-26.
Wintgens, T., Melin, T., Schafer, A., Khan, S., Muston, M., Bixio, D. and Thoeye, C. 2005. The role of
membrane processes in municipal wastewater reclamation and reuse. Desalination 178(1-3), 1-
11.
Xie, M., Lee, J., Nghiem, L.D. and Elimelech, M. 2015. Role of pressure in organic fouling in forward
osmosis and reverse osmosis. Journal of Membrane Science 493, 748-754.
Yang, H.L., Huang, C. and Pan, J.R. 2008. Characteristics of RO foulants in a brackish water
desalination plant. Desalination 220(1-3), 353-358.
Yin, R., Zhong, Z.Z., Ling, L. and Shang, C. 2018. The fate of dichloroacetonitrile in UV/Cl2 and
UV/H2O2 processes: implications on potable water reuse. Environmental Science-Water
Research & Technology 4(9), 1295-1302.
Yip, N.Y. and Elimelech, M. 2012. Thermodynamic and Energy Efficiency Analysis of Power Generation
from Natural Salinity Gradients by Pressure Retarded Osmosis. Environmental Science &
Technology 46(9), 5230-5239.
Zeng, T., Plewa, M.J. and Mitch, W.A. 2016. N-Nitrosamines and halogenated disinfection byproducts in
US Full Advanced Treatment trains for potable reuse. Water Research 101, 176-186.
Zhu, A.Z., Christofides, P.D. and Cohen, Y. 2009. Effect of Thermodynamic Restriction on Energy Cost
Optimization of RO Membrane Water Desalination. Industrial & Engineering Chemistry Research
48(13), 6010-6021.
Zohrabian, A., Plata, S.L., Kim, D., Childress, A.E. and Sanders, K.T. 2021. Leveraging the water-
energy nexus to derive benefits for the electric grid through demand-side management in the
water supply and wastewater sectors. WIREs Water.

Abstract (if available)

Abstract Water scarcity, a critical environmental issue globally, has primarily been driven by a significant increase in surface water and groundwater extractions due to increased global population, rising standards of living, and climate and societal changes. With the emergence of new technologies, alternative water sources supplied by wastewater reclamation, seawater desalination, and brackish water desalination are in rapid development. Wastewater reclamation and desalination provide independent supplies of water that can be cost-competitive and more reliable than importing/transferring water from other regions or collecting and treating stormwater runoff. Reclaimed wastewater and desalinated water undergo separate treatment and transport and are often not seen as the interconnected water resources that they are. Particularly in coastal water-scarce regions, where surface water sources have limited availability and groundwater sources may be fully allocated, wastewater reclamation and seawater desalination are important components of water supply portfolios. The main objective of this dissertation is to investigate synergistic systems for desalination and potable reuse and understand the impact of novel configurations on energy consumption and water recovery. Firstly, to investigate the synergistic blending opportunities of the waste streams from seawater reverse osmosis (RO) and wastewater treatment facilities, four scenarios?two discharge blending and two influent blending?were considered. A modeling framework was developed based on seawater RO facilities to evaluate required seawater and treated wastewater flowrates, discharge flowrates and components, boron removal, and system energy requirements. The best blending scenario to meet seawater RO brine discharge requirements was determined. Secondly, to critically evaluate the energy that will be consumed in recovery water from higher-salinity streams for additional influents at advanced water purification facilities, the benefits of additional influents are weighted against the additional energy consumption due to increased salinity in the influent. Opportunities to implement or enhance energy and water recovery using an energy recovery device in conjunction with RO or by using closed-circuit RO are considered. Also, a scenario of desalinating higher-salinity streams separately from treated wastewater is considered. Thirdly, to understand the energy consumption during potable reuse of higher-salinity streams, both theoretical minimum energy consumption and practical energy consumption are analyzed to compare energy consumption when using ERDs in conjunction with RO, and using high-recovery RO (e.g., closed-circuit RO) with a baseline. In addition, the theoretical minimum energy consumption of RO is compared with the practical energy consumptions to investigate the inefficiencies that can be targeted to bring the practical energy consumption closer to the theoretical energy consumption of RO.

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University of Southern California Dissertations and Theses

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Asset Metadata

Creator Wei, Xin (author)

Core Title Integrating systems of desalination and potable reuse: reduced energy consumption for increased water supply

School Viterbi School of Engineering

Degree Doctor of Philosophy

Degree Program Engineering (Environmental Engineering)

Degree Conferral Date 2021-08

Publication Date 07/22/2021

Defense Date 06/10/2021

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag desalination,energy consumption,integrating systems,OAI-PMH Harvest,potable reuse,Water supply

Format application/pdf (imt)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Childress, Amy (committee chair), Luhar, Mitul (committee member), McCurry, Daniel (committee member), Sanders, Kelly (committee member), Smith, Adam (committee member)

Creator Email wei383@usc.edu,weixincmu@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-oUC15616321

Unique identifier UC15616321

Legacy Identifier etd-WeiXin-9826

Document Type Dissertation

Format application/pdf (imt)

Rights Wei, Xin

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

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Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA

Repository Email cisadmin@lib.usc.edu