Intimately coupled TiO2/g-C3N4 photocatalysts and in-situ cultivated biofilms enhanced nitrate reduction in water

Nitrogen pollution has become a major threat to the aquatic environment, and the key to solve this problem is to enhance the nitrate reduction in water. Intimately coupled photocatalysis and biodegradation (ICPB) is a novel technique for degradation of bio-recalcitrant pollutants; however, it has not been used for nitrate reduction. This study applied a system that intimately coupled TiO2/g-C3N4 photocatalysts and in-situ cultivated biofilms for nitrate reduction in water without additional electron donors. The result shows a nitrate removal rate up to 40.3% in ICPB after 16 h. Furthermore, the N2 selectivity was 86.3%, which was higher than that for other protocols. In ICPB, nitrate was first reduced to nitrite, which was mainly contributed to the effect of biofilms. Then, nitrite was reduced via the cooperation of photocatalysts and biofilms, which benefited both low production of undesirable products and high selectivity of N2. Moreover, the growth of the microbes during the ICPB were favorable for denitrification. In conclusion, light-induced electrons generated from TiO2/g-C3N4 were harvested by microbes, optimizing the community structure of biofilms toward nitrate reduction. This study provides a new strategy to enhance the nitrate reduction in water and an insight into the reduction mechanism of nitrate in ICPB.