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CEE Oral Dissertation Defense
Tue, Jun 18, 2013 @ 02:00 PM - 04:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Student Activity
Ryan Thacher, ENE Ph.D. Candidate
Advisor: Prof. Massoud Pirbazari
Title:
Electrokinetic Transport of CrVI and Integration with Zero-Valent Iron Nanoparticle and Microbial Fuel Cell Technologies for Aquifer Remediation
Abstract:
Hexavalent chromium (CrVI) is a carcinogenic heavy metal used widely in industrial applications such as remediation in aquifers by the integration of electrokinetic transport phenomena with two novel CrVI reduction technologies: Chemical reduction by zero-valent iron nanoparticles (nZVI), and biological 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. Demonstrations of these technologies are performed on the laboratory-scale, using an electrokinetic cell charged with two different clay soils as well as a silica-sand typical to aquifers. The electrokinetic cell was designed to accommodate the control of critical variables to the electrokinetic remediation process.
Initial investigations involving clay soils determined CrVI adsorption was described well by the Langmuir adsorption isotherm model and experimental adsorption capacities for the two clay soils, kaolinite and EPK kaolin. However reduction rate studies by the clay soils indicated that EPK kaolin had an extremely high capacity for reducing CrVI through chemical reduction and physical adsorption, a result of natural organic matter (NOM) bound to the EPK kaolin particle surface. Comparisons between the soils highlighted the importance of NOM on the fate and transport of CrVI in aquifers, and also indicated that surface bound NOM could rapidly reduce CrVI, while dissolved NOM and CrVI complex only over long time periods. Electrokinetic column studies with the two clay soils reflected the initial findings in terms of CrVI transport observed, and also highlighted transport inhibition due to pH gradient formation that has been well described in literature.
To circumvent inherent problems with electrokinetic transport through clay soils and the need to work with a dynamic system, a sandy soil was used for the next set of studies investigating the integration of electrokinetic transport with nZVI addition for CrVI remediation. Initial reduction capacity studies determined the reduction capacity of nZVI to be nearly two times greater under anoxic conditions in comparison to oxygenated water containing humic acid. Results indicated that transporting CrVI to the site of nZVI injection was beneficial in optimizing the use of these technologies. Additionally, it was noted that a continuous flow system could mediate pH gradient formation, allowing for continual CrVI transport. The presence of humic acid in these studies did not effect electrokinetic transport however did lower the removal capacity of nZVI for CrVI.
Integrating electrokinetic transport with biological treatment in an MFC was evaluated as 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. 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.
Lastly, a transport study of CrVI through sandy soil was conducted without electrokinetic application. A sand column with Shewanella oneidensis MR-1 biofilm growth in sand media to simulate in situ biological treatment was exposed to a continuous-flow CrVI solution with and without humic acid, and an experimental breakthrough curve was developed. A similar experiment was conducted for a sand media coated in an iron oxide layer to simulate a permeable reactive barrier. A predictive model was modified for each column study to consider only the significant CrVI removal mechanisms (biodegradation and adsorption, independently) and was found to accurately represent the experimental data for both systems. A series of sensitivity analyses provided further insight into the dynamics of both column systems, and identified parameters essential to each process.
Location: Kaprielian Hall (KAP) - 209 Conference Room
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
