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

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 SO₄^2-. 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.