[Effect of Rate of Salinity Increase on the Performance and Microbial Community Structure of Sequencing Batch...

In this study, three sequence batch reactors were selected to evaluate the effects of salt-tolerant activated sludge acclimation. The effect of salinity increase rate on pollutant removal, physicochemical characteristics of activated sludge, and microbial community were investigated. The results showed that a rapid salinity increase to 30‰ (within 30 d) reduced removal efficiencies of COD and NH₄⁺-N from 85.5% and 98.5% (18 d) to 72.2% and 81.7% (51 d), respectively. In comparison, a slower salinity increases to 30‰ (within 90 d) had a minor effect on COD and NH₄⁺-N removal. During the rapid salinity increase, a stable shortcut nitrification occurred under 20‰ salinity, in which the effluent NO₂^--N reached 11.13 mg·L^-1 and NO₃^--N decreased to 0.56 mg·L^-1. When salinity increased to 30‰, the nitrite accumulation rate was about 90%, and the removal efficiency of total nitrogen increased to approximately 75%. The contents of polysaccharide and protein in extracellular polymer substances increased as salinity increased, and the polysaccharide content increased significantly when the salinity was higher than 15‰. High-throughput sequencing results illustrated that microbial diversity reduced as salinity increased, following the Shannon index decrease from 8.06 (0‰ salinity) to 4.34 (rapid salinity increase) and 6.17 (slower salinity increase). As salinity increased, Micropruina, Denitromonas, TM7a, and Marinicella exhibited good salt tolerance. The relative abundance of Denitratisoma, Defluviimonas, Arenimonas, and Denitromonas decreased more significantly following the rapid salinity increase compared with that after the slower salinity increase.