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Direct Fixed-Bed Biological Perchlorate Destruction Demonstration

Abstract : In February 2007, a 10-month demonstration study was initiated in Rialto, California to treat perchlorate-contaminated groundwater using fixed-bed (FXB) bioreactor technology. Two first-stage, parallel FXB bioreactors (F120 with a 3.9-ft bed depth and a 2-ft diameter, and F130 with a 4.7-ft bed depth and a 2-ft diameter) treated groundwater to remove perchlorate. Effluent from these reactors was dosed with hydrogen peroxide (i.e., reoxygenate + oxidize residual organics and hydrogen sulfide). The reoxygenated water was then passed through a FXB biofilter (F150) to oxidize any remaining organics and sulfide and to remove turbidity. Chlorine was then dosed to the effluent of the biofilter as a final disinfection step. In parallel with the pilot testing, a mathematical model was developed and calibrated, which can be used to elucidate observed phenomena during pilot testing and to predict the perchlorate removal performance of a FXB bioreactor system at other sites. Additionally, molecular microbiological analyses were performed to quantify the relative abundance of specific bacteria within the mixed microbial community in the bioreactor bed. A bench-scale FXB bioreactor was also constructed to test how nutrient addition and intermittent electron donor addition patterns affect the performance and microbial community of a bioreactor. Tests were run using the bench-scale bioreactor that could not be easily conducted using the demonstration-scale system.