Effect of hydraulic retention time on performance of an anoxic–aerobic sequencing batch reactor treating saline wastewater

The effects of hydraulic retention time on the performance and microbial community structure of an anoxic–aerobic sequencing batch reactor treating saline wastewater were investigated. The average removal efficiencies of chemical oxygen demand and ammonia nitrogen decreased from 90 and 85 % to 68 and 71 % with the decrease in hydraulic retention time from 17 to 9 h, respectively. No obvious accumulation of nitrate nitrogen and nitrite nitrogen in the effluent was found. The contents of polysaccharide and protein in extracellular polymeric substances increased with the decrease in hydraulic retention time. The polysaccharide/protein ratio decreased from 1.18 to 1.11 with the decrease in hydraulic retention time from 17 to 9 h. The increase in extracellular polymeric substances with the decrease in hydraulic retention time led to the increase in sludge volume index. The specific ammonium oxidation rate, specific nitrite oxidation rate, specific nitrate reduction rate, and specific oxygen uptake rate increased with the decrease in hydraulic retention time. The diversity indices of microbial community decreased from 2.69 to 2.39 with the decrease in hydraulic retention time from 17 to 9 h. The α-proteobacteria were the dominant groups under hydraulic retention time of 17, 14, 11, and 9 h, which constituted 46, 30, 40, and 40 % of the whole microbial community, respectively.