Bioreduction of selenate in an anaerobic biotrickling filter using methanol as electron donor.

The anaerobic bioreduction of selenate, fed in step (up to 60 mg.L-1) or continuous (∼7 mg.L-1) trickling mode, in the presence of gas-phase methanol (4.3-50 g m-3.h-1) was evaluated in a biotrickling filter (BTF). During the 48 d of step-feed and 41 d of continuous-feed operations, average selenate removal efficiencies (RE) > 90% and ∼68% was achieved, corresponding to a selenate reduction rate of, respectively, 7.3 and 4.5 mg.L-1.d-1. During the entire period of BTF operation, 65.6% of the total Se fed as SeO42- was recovered. Concerning gas-phase methanol, the maximum elimination capacity (ECmax) was 46.4 g m-3.h-1, with a RE > 80%. Methanol was mainly utilized for acetogenesis and converted to volatile fatty acids (VFA) in the liquid-phase. Up to 5000 mg.L-1 of methanol and 800 mg.L-1 of acetate accumulated in the trickling liquid of the BTF.