Bio-reduction mechanism of V(V) by thermophilic hydrogen-producing bacteria under acidic conditions

Abstract

To solve the challenge caused by the higher temperature and lower pH of industrial vanadium-containing wastewater, a research on the reduction of vanadium by thermophilic bacteria was conducted at 55 °C and pH 4.2–5.8 in an anaerobic hydrogen fermenter. Results show that 100 mg L⁻¹ of V(V) can be completely reduced (97.75%) to tetravalent vanadium (V(IV)) through biological and chemical pathways. Thermophilic Bacilli and Clostridia dominate V(V) reduction in the first-order exponential decay mode. Both glucose and metabolites (volatile fatty acids and hydrogen) serve as electron donors, and the addition of glucose shows better enhancement for V(V) reduction than the addition of acetic acid. Thermophilic hydrogen-producing bacteria enhance the reduction of V(V) by regulating the intracellular metabolism and secretion of extracellular polymers. Extracellular NADH, riboflavin, and intracellular glutathione (GSH) play important roles in V(V) reduction. The results suggest that thermophilic hydrogen-producing bacteria can be used for V(V) reduction at higher temperatures, and provide a reference for the development of the V(V) biological reduction technology.