Glucose as a dual-functional co-substrate in intimately coupled photocatalysis and biodegradation systems: Synergistic enhancement of refractory organics mineralization and nitrate removal.

Nitrate contamination threatens water quality and human health; however, conventional denitrification treatment strategies struggle in complex wastewater due to the low bioavailability of refractory organics. The intimately coupled photocatalysis and biodegradation (ICPB) system addresses this by transforming recalcitrant compounds into usable electron donors, enabling simultaneous nitrate and organic pollutant removal. This study demonstrates that adding a small dose of glucose (50 mg/L chemical oxygen demand) to the ICPB system enhanced performance by increasing organic mineralization from 53 % to 81 % and total nitrate and nitrite removal from 40 % to 93 %. Supplementing the ICPB system with glucose significantly stimulated microbial activity. The heightened activity accelerated the mineralization of photocatalytically-derived intermediates, preventing toxic byproduct accumulation. Microbial inhibition was reduced from 68 % to 20 %, further enhancing the pollutant removal efficiency of the ICPB system. Additionally, glucose functioned as an auxiliary electron donor, concurrently enhancing denitrification. Metagenomic analysis suggested that riboflavin biosynthesis upregulation may have promoted electron transfer, potentially boosting system efficiency. This strategy offers a simple and effective means to optimize the synergistic removal of refractory organics and nitrate during wastewater treatment.