Synchronous vanadium bio-reduction/detoxification/recovery and nitrogen attenuation in a membrane aerated biofilm reactor

Abstract

The presence of both pentavalent vanadium [V(Ⅴ)] and nitrogen in wastewaters from vanadium smelting poses significant environmental challenges. However, it remains little in the way of continuous flow biological reactor to concurrently eliminated V(Ⅴ) and nitrogen in wastewaters. Herein, membrane-aerated biofilm reactor (MABR) system was designed to achieve simultaneous nitrification and denitrification (SND) alongside biological reduction, detoxification, and recovery of vanadium. Vanadium and nitrogen removal performances, solid-state characterization, microbial compositions and functional genes, and the mechanism related to the metabolism of vanadium and nitrogen were illuminated. Notably, we identified a potential role for biofilm-derived “secretion” in the transformation of V(Ⅴ) and nitrogen. Our findings revealed that the system achieved SND efficiency of 98.00 ± 0.57 % and removed 91.10 ± 3.60 % of total vanadium (TV) even at high influent V(Ⅴ) concentrations in continuous flow stage. Batch experiments implied that the conversion of NH₄⁺-N was the limiting process of nitrogen removal in MABR system, and the extracellular polymeric substances (EPS) might play an important role in the conversion of V(Ⅴ) and nitrogen. V(Ⅴ) was reduced to V(Ⅳ), which was immobilized to biofilm and “secretion” by microbial surface functional groups, including C-O, O-C=O and -OH. Acinetobacter, Dechlorobacter, Denitratisoma and Nitrospira were verified as microbes associated with V(Ⅴ) and nitrogen metabolism. The abundance of functional genes pertaining to electron donor, electron transport, and electron acceptor systems increased under high V(V) stimulation. Collectively, the cooperation of biofilm and “secretion” ensured the intensive removal of vanadium and nitrogen. This study provides new insights into the concurrent removal of heavy metal and environmental nutrient.