Microalgal-bacterial biofilms enhance pollutant removal coupling with eicosapentaenoic acid production in high-concentration ammonia‑nitrogen wastewater

Microalgal-bacterial biofilms have emerged as a promising approach for wastewater treatment. However, its potential to treat high-concentration ammonia‑nitrogen wastewater coupling with high-value fatty acid production remains unclear. Therefore, this study explored the efficiency of a microalgal-bacterial biofilm in treating high-concentration ammonia‑nitrogen wastewater and its ability to produce high-value fatty acids, with the activated sludge (bacteria) and microalgal-bacterial suspension as control. The results indicated that pollutant removal in the microalgal-bacterial biofilm system was the most efficient, with a 98.3 % removal efficiency for chemical oxygen demand, 87.46 % for ammonium nitrogen, and 20.6 % for phosphate. Coupling analysis of microbial community shift and nitrogen conversion genes showed that the relative abundance of Rhodanobacter and Nitrosomonas significantly increased in microalgal-bacterial biofilms, and the expression of nitrification-related genes (amo and hao) and denitrification-related genes (nasA,napA, narI, narV, nirK, and norB) increased compared to the control systems, which played an important role in nitrogen removal. The microalgal-bacterial biofilm system exhibited higher levels of fatty acid synthase and omega-6 fatty acid desaturation, resulting in a dry weight content and production of eicosapentaenoic acid (EPA) with 15.8,19.1 times greater than that achieved by the microalgal suspension system. These results present a foundation for application of pollutant removal in high ammonia nitrogen wastewater coupling with high-value acid production by microalgal-bacterial biofilms.