The interplay of sulfate and nitrate triggers abiotic reduction in a hydrogen-based membrane biofilm reactor for antimonate removal

[Display omitted] •The increase of SO42– loading enhanced the Sb(V)- and total Sb- removal.•90% Sb(V) removal flux (0.76 g/m2·day) was achieved due to the input of sulfate.•The exposure of nitrate led to Sb2S3 oxidation coupled to NO3– reduction.•Sulfide was produced microbially as the reductant for Sb(V) removal.•The mechanisms of biofilm action exposed to oxidized Sb, S, and N were summarized. Sb is classified as a priority pollutant, to control the pollution in aquatic environments of Sb, enhance the understanding of Sb biogeochemical cycle, the effects of sulfate and nitrate on antimonate (Sb(V)) removal in a Hydrogen-Based Membrane Biofilm Reactor (H2-MBfR) were investigated. With the input of sulfate, the MBfR achieved 90% Sb removal and a removal flux up to 0.76 g Sb/m2·day. The Sb(V) was reduced to Sb(III), which was primarily Sb2S3 solids retained in the biofilm. Furthermore, the mechanism of antimonate reduction shifted from enzymatic reduction with no sulfate input to abiotic reduction based on sulfide produced microbially being the reductant. The subsequent input of nitrate suppressed Sb(V) reduction and removal, along with suppressing sulfate reduction. Nitrate became the dominant electron acceptor, which led to Sb2S3 oxidation and the net release of Sb(V) and SO42-. This work reinforces that the H2-MBfR is a promising bioremediation strategy for antimonate removal, and it provides mechanistic insights regarding the impacts of sulfate and nitrate on antimonate reduction and removal.