Gas-phase methanol fed anaerobic biotrickling filter for the reduction of selenate under step and continuous feeding conditions

90The 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 SeO₄ ²⁻ was recovered. Concerning gas-phase methanol, the maximum elimination capacity (EC_max) was 46 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.