Concurrent vanadate and ammonium abatement in a membrane biofilm reactor

Abstract

Ammonium (NH4+) is commonly used as either a precipitant or extractant in metallurgy of non-ferrous metal and rare earth ore (e.g., vanadium). This results in the coexistence of toxic metal and NH4+-N in the effluent. Despite its toxicity, there remains little in the way of biological treatments to synchronously eliminate vanadate [V(V)] and NH4+-N in vanadium smelting wastewater. In this study, simultaneous V(V) and NH4+-N removal was achieved using a membrane biofilm reactor (MBfR). The removal efficiencies for V(V) and NH4+-N reached 96.8 ± 0.8% and 75.4 ± 1.2%, respectively, with initial concentrations for both beginning at 10 mg/L along with a hydraulic retention time at 36 h. V(V) was mainly reduced to V(IV) precipitates. Complete nitrogen removal was achieved with negligible NO3–-N/NO2–-N accumulation. Pseudomonas was identified as the main contributor to V(V) reduction, nitrification, and denitrification. The identified V(V) reducers and nitrifying/denitrifying bacteria were positively related to the V(V) and NH4+-N removal capacity of MBfR. The increased gene abundance and improved enzymic activity for nitrogen cycling collectively evidenced that V(V) reduction was catalyzed by denitrification enzymes and NH4+-N was removed through nitrification/denitrification. Collectively, the results from this study offer a novel strategy for the treatment of vanadium-bearing smelting wastewater by eliminating V(V) and NH4+-N in a one-step bioprocess.