Enhanced nitrate removal through electrochemical and microbial synergy in photocatalytic-microbial wastewater...

Photocatalytic-microbial biohybrid systems provide a sustainable approach for treating nitrate-laden wastewater with low carbon-to-nitrogen (C/N) ratios. However, the mechanism by which photoelectrons enhance quorum sensing (QS) to integrate electrical and chemical signals and improve nitrate removal remain poorly understood. In this study, carbon dot-modified Fe-doped bismuth molybdate (CD/Fe-BMO) composites were synthesized and applied to anaerobic sludge systems, increasing the nitrate removal rate by 23.21 %. Mechanistically, the photocatalysis of CD/Fe-BMO reshaped microbial communities and enriched low-abundance electroactive microorganisms involved in organic degradation and denitrification. Meanwhile, CD/Fe-BMO accelerated transmembrane electron transfer, stimulated microbial metabolism activities, and promoted QS-associated key functions, including chemotaxis, biofilm formation, and extracellular polymeric substance secretion. Cascade regulation mediated by signal molecule further enhanced electron transfer efficiency. Together, photocatalysis and QS established a synergistic mechanism that reinforced microbial carbon metabolism and denitrification, highlighting CD/Fe-BMO as a promising photocatalyst for efficient nitrate-laden wastewater treatment under low C/N ratios.