Effect of external carbon addition and enrofloxacin on the denitrification and microbial community of sequencing batch membrane reactor treating synthetic mariculture wastewater.

The effect of sequencing batch membrane bioreactor (SMBR) on external carbon addition and enrofloxacin was investigated to treat synthetic mariculture wastewater. Anoxic/anaerobic and low COD/TN can improve the ammonia oxidation of the system, and the NH4+-N removal efficiency above 99%. External carbon was added and an anoxic environment was set to provide a suitable environment for denitrifying bacteria. When the external carbon source was 50-207 mg/L, the TN removal efficiency (31.82%-37.73%) and the COD of the effluent (28.85-36.58 mg/L) had little change. The partition resistance model showed that cake deposition resistance (RC,irr) and irreversible resistance (RPB) were the main components. And with the increase in cleaning times, the fouling rate of membrane components accelerated. Enrofloxacin can promote the TN removal efficiency (45.66%-93.74%) and had a significant effect on TM7a, Cohaesibacter, Vibrio and Phaeobacter.

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

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.