Sustained perchlorate degradation in an autotrophic, gas-phase, packed-bed bioreactor

An autotrophic packed-bed biofilm reactor was operated in unsaturated-flow mode and continuously fed water containing perchlorate (ClO4-) (as an electron acceptor) and a gas mixture of hydrogen (5%) and carbon dioxide. The reactor was inoculated with a perchlorate-reducing, hydrogen-oxidizing autotrophic bacterial consortium and run for 10 days at a perchlorate feed concentration of 50 mg/L to build up biofilm on the reactor packing. The reactor feed was then switched to a lower influent perchlorate concentration of 740 µg/L. Over a 140-day period at a constant hydraulic loading rate of 0.45 cm/min, 38±9% of the perchlorate was removed in the reactor at detention times of 1.1-1.3 min producing an average removal rate of perchlorate of 230 µg L-1 min-1. To study in more detail perchlorate degradation kinetics, a hydrogen-oxidizing microorganism (Dechlorimonas sp. JM) was isolated from the bacterial consortium. Batch kinetic tests indicated hydrogen and perchlorate half-saturation constants of KH = 0.036±0.014 mM H2(I) and Kp = 0.15±0.06 mM, respectively. The high perchlorate degradation rates and long-term performance of this system demonstrate the feasibility of this novel unsaturated hydrogen gas-phase fixed-film bioreactor for treatment of perchlorate-contaminated water.