Enhanced denitrification performance and biocatalysis mechanisms of polyoxometalates as environmentally-friendly inorganic redox mediators

Polyoxometalates (POMs) used in chemical catalysis field were first explored their effect on the denitrification process. Experiments demonstrated that NO3--N reduction rate with 0.05 mM phosphomolybdic acid (PMo12) was approximately 3.93-fold higher than the PMo12-free system. Simultaneously, PMo12 also had positive effect on NO2--N reduction. Compared with the PMo12-free system, the solution resistance and oxidation-reduction potential were decreased, and the activation energy (Ea) was reduced by 51.84 kJ/mol. Besides, electron conductive substances in extracellular polymeric substances were stimulated by PMo12. NADH and riboflavin were enhanced to increase denitrification electron transport system activity. Higher microbial diversity and enrichment of Salmonella were observed in the PMo12-supplemented system. Based on the above analysis, the catalyzing mechanisms of PMo12 are proposed that PMo12 made it easier for electron transferring from electron donor to electron acceptor and shifted bacterial community structure. These findings may provide a promising strategy for nitrogen wastewater treatment.