Removal of perchlorate from ground water by hydrogen-utilizing bacteria

An autotrophic consortium of bacteria, utilizing hydrogen and bicarbonate as electron and carbon sources, respectively, for the reduction of perchlorate has been enriched. The efficiency of this consortium for perchlorate reduction in a packed-bed bioreactor is described. The use of hydrogen as an electron source for microbial biodegradation of pollutants in a packed-bed bioreactor is advantageous because hydrogen does not promote vigorous biomass growth, resulting in less clogging of the system, and hydrogen gas reduces the need for postreactor water cleanup. The consortium, comprised of four bacteria, was capable of removing nitrate and perchlorate simultaneously from mineral salts medium in a batch culture. A 120-mL bioreactor was designed to test the capacity of the consortium to remove perchlorate in a flow-through system. At a flow rate of 1 mt min(-1), perchlorate levels naturally occurring in San Gabriel Valley ground water (0.740 mg L-1) were completely removed to less than 0.004 mg L-1, which is the detection limit. However, as the flow rate was increased, the removal efficiency decreased. Factors affecting the rate of perchlorate removal included nonuniform distribution of biomass in the column, unstable pH of the ground water, and limited delivery of hydrogen to the bacteria. This bioreactor also completely removes perchlorate from ground water at a flow rate of 1 mt min(-1) without an added carbon source, presumably using the bicarbonate naturally present in the ground water.