Perchlorate remediation using packed-bed bioreactors and electricity generation in microbial fuel cells (MFCs)
Abstract (Summary)iii Two pilot-scale fixed bed bioreactors were operated in continuous mode in order to treat groundwater contaminated by perchlorate. The bioreactors were constructed and operated side-by-side at the Texas Street Well Facility in Redlands, Californian. Each reactor was packed with either sand or plastic media. A perchlorate-reducing bacterium, Dechlorosoma sp. KJ, was used to inoculate the bioreactors. Perchlorate was successfully removed down to a non-detectable level (< 4µg/L) in both bioreactors with acetate as a carbon source and nutrients at loading rates less than 0.063 L/s (1 gpm; 0.34 L/m 2s). The sand medium bioreactor could achieve complete-perchlorate removal up to flow rate of 0.126 L/s. A regular backwashing cycle (once a week) was an important factor for completely removing perchlorate in groundwater. Power generation directly from pure or mixed organic matter was examined using microbial fuel cells (MFCs), which were run either in batch or continuous mode. In batch experiments, both a pure culture (Geobactor metallireducens) and a mixed culture (wastewater inoculum) were used as the biocatalyst, and acetate was added as substrate in the anode chamber of the MFC. Power output in a membrane MFC with either inoculum was essentially the same, with 40 ± 1 mW/m 2 for G. metallireducens and 38 ± 1 mW/m 2 for mixed culture. A different type of the MFC containing a salt bridge instead of a membrane system was examined to generate power using the same substrate and pure culture as used in the membrane MFC. Power output in the salt bridge MFC was 2.2 mW/m2. It was found that the lower power output was directly attributed to the higher internal resistance of the salt bridge system (19920 ± 50 ?) in comparison with that of iv the membrane system (1286 ± 1 ?). Continuous electricity generation was examined in a flat plate microbial fuel cell (FPMFC) using domestic wastewater and specific organic substrates. The FPMFC, containing a combined electrode/proton exchange membrane (PEM), was initially acclimated for one month to domestic wastewater, and then was operated as a plug flow reactor system. Power density using domestic wastewater as a substrate was 72 ± 1 mW/m2 at a liquid flow rate of 0.39 mL/min (1.1 hr hydraulic retention time, HRT), and COD removal was 42 %. At a longer HRT of 4.0 hr, the COD removal increased to 79%, and power density was 43 mW/m 2. Several organic compounds (about 1000 mg-COD/L) also generated high power densities including: glucose (212 ± 2 mW/m 2), acetate (286 ± 3 mW/m2), butyrate (220 ± 1 mW/m2), dextran (150 ± 1mW/m 2), and starch (242 ± 3mW/m2). Therefore, it was shown that power could be successfully generated in a continuous-mode MFC with a variety of organic substrates. Animal wastewater was also tested as substrate to generate power in an aircathode single chamber MFC operated in batch mode. This preliminary experiment demonstrated that power generation could be sustained with animal wastewater and that wastewater strength and odors were substantially reduced in the reactor after only one day of operation.
School Location:USA - Pennsylvania
Source Type:Master's Thesis
Date of Publication: