Low Carbon to Nitrogen Ratio Bacterial Algae Symbiotic Nitrogen Removal System

Microalgal-bacterial symbiotic system is expected to efficiently treat ammonia nitrogen wastewater at low carbon-to-nitrogen ratio (CNR). In this study, MBSS was constructed and operated at CNRs of 0, 2, and 4 for 36 days, named as L (low CNR), M (medium CNR), and H (high CNR). Microbial interaction mechanisms were explored through integrated metagenomics and non-targeted metabolomics. The average NH4+-N removal efficiencies of L, M, and H were 9.2 %, 33.6%, and 51.6%, respectively. CNR significantly influenced NH4+-N removal. Metagenomics and metabolomics showed that bacteria dominate MBSS, with the phylum Pseudomonadota having a large advantage. Addition of simple organic carbon sources may inhibit the generation of complex organic compounds by microalgae, consequently leading to bacteria utilizing simple carbon sources. Certain key microorganisms, genes, and metabolites respond to different CNRs to regulate MBSS performance. These results suggest that low CNR profoundly affects MBSS operation.