In situ bioremediation of perchlorate in vadose zone soil using gaseous electron donors: microcosm treatability study.

A series of microcosm experiments were performed to determine the effectiveness of various gaseous electron donors (including hydrogen, 1-hexene, ethyl acetate, and liquefied petroleum gas [LPG]) for supporting biological perchlorate reduction under different electron donor concentrations and soil moistures. Under high soil moisture (16% w/w) conditions, complete or partial perchlorate degradation was achieved with all of the tested electron donors, except for ethyl acetate. Hydrogen was the most promising of the tested electron donors, achieving complete perchlorate degradation with first-order rate constants ranging from 0.13 to 0.20 day(-1) and reducing concentrations to non-detectable levels within 35 to 42 days. The LPG and 1-hexene each promoted partial perchlorate reduction, with average first-order rate constants of 0.05 and 0.11 day(-1), respectively. Although significant perchlorate reduction was observed with as little as 13% moisture, the moisture content for complete perchlorate degradation in this particular soil was determined to be 17%.