Research on the heterotrophic ammonia assimilation and denitrification efficiency of activated sludge in saline wastewater
Saline industrial wastewater exerts a significant inhibitory effect on biological wastewater treatment. In this study, acclimated activated sludge resistant to high salinity shock was used to establish an internal-bag limited aeration mode in a batch reactor, inducing ammonia assimilation for nitrogen removal under high-salinity conditions. Simultaneous and efficient removal of TN, NH4+-N, and COD was achieved within 24 hours, with TN and NH4+-N removal efficiencies reaching 73.96% and 74.74%, respectively, and a COD removal efficiency of 84.09%. The denitrification process generated negligible amounts of NO3--N and NO2--N. Furthermore, the effects of influent carbon source type, C/N ratio, pH, and sludge concentration on the nitrogen removal efficiency of the ammonia assimilation system were investigated. The results showed that under an influent NaCl concentration of 10 g/L, sodium acetate was the optimal external carbon source. The optimal conditions for nitrogen removal were identified as a C/N ratio of 9, pH of 8.0 0.1, and a sludge concentration of 3000 mg/L. Microbial community analysis revealed that at the phylum level, the dominant ammonia-assimilating phylum (Chloroflexota), carbon-fixing phylum (Thermodesulfobacteriota), and salt-tolerant phylum (Pseudomonadota) were significantly enriched. At the genus level, the relative abundance of Pseudomonas, a genus with ammonia-assimilating capacity, increased, while the relative abundance of Flavobacterium, a genus responsible for nitrate reduction and denitrification, significantly decreased, confirming that denitrification was inhibited in this reactor and that ammonia assimilation was the dominant nitrogen removal pathway.