Enhanced Anaerobic Biodegradation of PCBs in Contaminated Sediments using Hydrogen
Ravikumar Srirangam, PhD Candidate, Advisor: Dr. Khodadoust
I am currently conducting research on remediation and destruction of Polychlorinated biphenyls (PCBs) in contaminated fresh-water sediments. The release of PCBs from sediments to overlying waters can occur by desorption, especially when PCB concentrations are high or when sudden hydrographic activity like flooding or dredging causes sediments to be re-suspended and redistributed. Due to their environmental persistence, PCBs have the tendency to biomagnify in the higher trophic levels of the food chain, and therefore pose potential health risks. PCBs are suspected to cause cancer or adverse skin and liver effects.
Biostimulation of anaerobic biodegradation of PCBs by the amendment of appropriate electron donors like hydrogen to contaminated sediments should stimulate the reductive dechlorination process. Addition of elemental zerovalent iron (Fe0) for production of hydrogen in contaminated sediments may enhance the microbial dechlorination of the PCBs which can be an efficient biostimulation technique for remediation and destruction of PCBs. Factors like pH, hydrogen levels, concentration of PCBs and microbial populations in sediments could be vital in governing the anaerobic biodegradation process. Microcosm experiments performed on contaminated sediments obtained from Lake Hartwell and Indiana Harbor (Lake Michigan) will give a clear idea on the effect of direct and indirect addition of electron donor on PCB biodegradation. Addition of controlled amounts of microscale iron metal to sediments has the potential to be developed as an efficient and cost effective technology for remediation and destruction of PCBs in contaminated sediments by providing a continuous source of electron donor for anaerobic biodegradation.
Leaching Characteristics of Arsenic from Aged Alkaline Coal Fly Ash
Pratibha Naithani, PhD Candidate, Advisor: Dr. Khodadoust
The focus of my research is to determine the chemical composition and leaching characteristics of arsenic from alkaline aged coal fly ash samples collected from Retired Ash Basin at Brunner Island site belonging to PPL Generation Company. Groundwater near the aged coal fly ash impoundment is affected by arsenic contamination from ash leachate. Arsenic is adsorbed on subsurface soils from leachate and contaminates groundwater. Arsenic is listed as one of 129 priority pollutants by the Environmental Protection Agency. Arsenic causes skin problems and several internal cancers, chronic exposure to high levels of arsenic results in cardiovascular and neurological disorders. The toxic effects of arsenic are related to its oxidation state. The main factors which affect leaching of arsenic are pH, Eh, calcium, inorganic carbon. Multiple batch sequential leaching tests and column leaching experiments have been performed. Coal fly ash was found to be overall dependent on the pH of ash samples. Despite the high iron content of ash, and the association of arsenic with the iron oxide fraction of ash, little or no iron leached out from ash under ambient pH conditions. The calcium content of ash mainly determined the pH of ash, where calcium was mostly in the form of CaCO3 and CaO in ash. The main calcium compounds present in the leachate system were CaSO4, CaCO3, Ca(HCO3)2and CaHAsO4. The pH was controlled by calcium bicarbonate present in the system. Arsenic leached out mainly as calcium hydrogen arsenate from the calcium arsenate present in ash. Batch and column leaching experiments have shown the similarity of leaching parameters for arsenic in both systems. Column leaching of ash samples from other depths at same location is expected to be similar to the batch leaching results for those samples.