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Electrokinetic Transport of CrVI and Integration with
Zero-Valent Iron Nanoparticle and Microbial Fuel
Cell Technologies for Aquifer Remediation
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(ENVIRONMENTAL ENGINEERING)
By
Ryan Thacher
August 2013
Object Description
| Title | Electrokinetic transport of Cr(VI) and integration with zero-valent iron nanoparticle and microbial fuel cell technologies for aquifer remediation |
| Author | Thacher, Ryan |
| Author email | rythach@gmail.com;rthacher@usc.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Environmental Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2013-06-18 |
| Date submitted | 2013-08-01 |
| Date approved | 2013-08-01 |
| Restricted until | 2013-08-01 |
| Date published | 2013-08-01 |
| Advisor (committee chair) | Pirbazari, Massoud |
| Advisor (committee member) |
Lynett, Patrick Prakash, Surya Shing, Katherine |
| Abstract | Hexavalent chromium (CrVI) is a carcinogenic heavy metal that is a product of many industrial processes. In its hexavalent state, chromium exists in the anionic form of chromate and dichromate, which are both stable and highly soluble in water. Once introduced to the environment, CrVI species can percolate through soils and reach the water table. From here CrVI can spread quickly throughout an aquifer as it moves naturally with the groundwater flow. Remediation of aquifers contaminated with CrVI is typically energy intensive, a slow process, and can be highly invasive. The study presented here investigates alternative remediation options for CrVI through the integration of effective contaminant transport and novel treatment technologies. It was determined that contaminant transport by electrokinetic technology can be used in conjunction with zero-valent iron nanoparticles (nZVI) for CrVI reduction, and also integrated with microbial reduction in a microbial fuel cell (MFC). NZVI have been proposed as an economic and effective in situ remediation technology, capable of rapidly reducing CrVI species to insoluble and non-toxic Crᴵᴵᴵ species. MFC technology is capable of reducing CrVI through microbiological mechanisms, and is viewed as a potential renewable energy resource. Both of these technologies are environmentally conscious alternatives to many conventional remediation approaches. ❧ Electrokinetic contaminant transport has been proposed to be effective for contaminated groundwater in soils of low hydraulic conductivity such as clay. Thus, initial electrokinetic investigations were performed using two different clay soils, EPK kaolin and kaolinite. Bench-scale isotherm and rate studies were performed to characterize the interaction between the two clay soils and CrVI. It was found that EPK kaolin had an extremely high capacity for reducing CrVI through chemical reduction and physical adsorption, resulting from natural organic matter (NOM) bound to the EPK kaolin particle surface. Comparisons between the soils indicated the importance of NOM on the fate and transport of CrVI in aquifers, and also highlighted the significance of surface bound NOM relative to dissolved NOM in the water matrix. Surface bound NOM was shown to rapidly interact with CrVI driving its reduction to Crᴵᴵᴵ species, while dissolved NOM and CrVI formed complexes over relatively long time periods. Electrokinetic column studies with the two clay soils reflected these initial findings, and also highlighted transport inhibition due to pH gradient formation, as described in literature. ❧ To circumvent inherent problems associated with electrokinetic transport through clay soils, a sandy soil was used for the continuous-flow column studies. This work focused on the integration of electrokinetic transport with nZVI addition for CrVI remediation, and evaluated the effects of NOM. Since transport of nZVI through subsurface formations has been shown to be difficult, it was decided that using electrokinetic transport to move contaminants to the point of nZVI injection could be effective. A series of adsorption/reduction studies and rate experiments determined the reduction capacity of nZVI to be nearly two times greater under anoxic conditions in comparison to oxygenated water containing naturally occurring groundwater constituents such as humic acid and calcium ion, and indicated rapid reaction kinetics. Electrokinetic transport experiments with nZVI injection showed that transporting CrVI to the site of nZVI injection was beneficial in terms of reducing the amount of nZVI required for treatment, and overall treatment time. Additionally, the continuous-flow system eliminated pH gradient formation, allowing for continual CrVI transport. The presence of humic acid in these studies did not effect electrokinetic transport of CrVI, however did lower its removal by nZVI. In a pilot- or full-scale nZVI treatment system, it seems appropriate to place a number of nZVI injection wells at strategic locations in the aquifer to optimize treatment, however for the sake of simplicity and ease of evaluation only one injection location was used in the experimental studies. ❧ An alternate treatment approach using biological systems was evaluated following the work with nZVI, as bacteria have been shown to effectively reduce CrVI. This was conducted through the integration of electrokinetic transport with microbial treatment in an MFC - a green alternative to traditional pump-and-treat remediation systems. In a continuous-flow system, electrokinetic transport of CrVI was found to reduce the treatment time for a given volume of contaminated water, and improved power output from the MFC. The MFC proved to be a sustainable treatment approach as well, reducing an influent contaminant stream to non-detectable CrVI concentrations for 12 days. Introduction of humic acid to the system to represent NOM also resulted in an improvement in the reduction of CrVI. Humic acid extended the breakthrough time for CrVI by almost 2 days in the sustainability studies relative to a system without humic acid. In the MFC systems, humic acids were shown to serve the role of an electron shuttle, a terminal electron acceptor, and reduced the bioavailability of soluble Crᴵᴵᴵ species, which are toxic to the microorganisms by complexation reactions. Similar to the continuous-flow system with nZVI injection, the MFC-electrokinetic system did not experience pH gradient formation, resulting in effective CrVI transport for the duration of the study. Microbial reduction was effective in these studies, however a single culture of bacteria cannot reduce CrVI indefinitely. The toxic nature of CrVI and soluble CrIII species to microorganisms is undeniable, however bacteria can be prepared as needed cost effectively. In the context of an MFC, as performance deterioration is observed one would simply replace the electrodes and introduce a new batch of bacteria to the cell, a renewable resource for remediation. ❧ The MFC studies inspired an interest in in situ biological reduction of CrVI in the context of microbial injection. Injecting microbes specific for a remediation task directly to a contamination plume is a remediation approach currently practiced. A column charged with Shewanella oneidensis MR-1 biofilm growth in sand media to simulate in situ biological treatment (biotic column) was exposed to a continuous-flow CrVI solution with and without humic acid, and experimental breakthrough curves were developed. A similar experiment was conducted for an iron oxide coated sand (IOCS) media to simulate a permeable reactive barrier (abiotic column), another groundwater treatment approach currently utilized. Two separate predictive models were employed to investigate CrVI reduction by i) microbial biofilm (biotic column), and ii) IOCS adsorptive layer (abiotic column). The predictive models were shown to accurately describe the experimental breakthrough data. A series of sensitivity analyses provided further insight into the dynamics of both column systems, highlighted the degree of influence of each parameter to system dynamics. The model was run for the IOCS system using input flow rates comparable to those observed in groundwater systems to simulate the performance of IOCS as a permeable reactive barrier. The results reflected the high adsorptive capacity of IOCS, and highlighted the utility of such predictive models for design purposes. |
| Keyword | electrokinetic; zero-valent iron nanoparticle; microbial fuel cell; hexavalent chromium; groundwater |
| Language | English |
| Format (imt) | application/pdf |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m |
| Contributing entity | University of Southern California |
| Rights | Thacher, Ryan |
| Physical access | The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright. The original signature page accompanying the original submission of the work to the USC Libraries is retained by the USC Libraries and a copy of it may be obtained by authorized requesters contacting the repository e-mail address given. |
| Repository name | University of Southern California Digital Library |
| Repository address | USC Digital Library, University of Southern California, University Park Campus MC 7002, 106 University Village, Los Angeles, California 90089-7002, USA |
| Repository email | cisadmin@dots.usc.edu |
| Filename | etd-ThacherRya-1918.pdf |
| Archival file | uscthesesreloadpub_Volume7/etd-ThacherRya-1918.pdf |
Description
| Title | Page 1 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@dots.usc.edu |
| Full text | Electrokinetic Transport of CrVI and Integration with Zero-Valent Iron Nanoparticle and Microbial Fuel Cell Technologies for Aquifer Remediation A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (ENVIRONMENTAL ENGINEERING) By Ryan Thacher August 2013 |
