Characteristics Of Nitrogen And Phosphorus Removal And Microbial Community In Modified A~2O-Sidestream Phosphorus Removal

The side-stream phosphorus removal technology and modified anaerobic/anoxic/aerobic (A2O) process were combined together to treat the effluent from an aeration grit chamber of sewage treatment plant and the ability of nitrogen and phosphorus removal were investigated under the condition of low carbon source, limited aeration and long sludge time. Meanwhile, the modern biology methods were used to analysis the microbial community structure, composition and relative abundance of activated sludge. The results showed that:1) under the condition of gradual-increasing aeration mode, dissolve oxygen was allocated properly and saved 33% aeration rate. Besides, the system achieved high nitrogen removal efficiency, which removal rate of COD, NH4+-N, TN were 72%,95.8%,51.1%, respectively and the effluent were 27.5 mg·L-1,0.65 mg·L-1,15.1 mg·L-1 respectively; 2) Adding anoxic tank in front of anaerobic zone reduced nitrate concentration by denitrification, resulting that nitrate was less 1.5 mg·L-1 and phosphorus release was eased as well; 3) the greater the amount of side-stream were, the better TP removal efficiency would be and when the side-stream sludge were returned back anoxic zone, the TP removal efficiency would be better than that of anaerobic zone and aerobic zone; 4) Side-stream phosphorus removal and alternately changing of anaerobic/anoxic/aerobic could enrich phosphorus-accumulating organisms(PAOs) and denitrifying phosphorus-accumulating organisms (DNPAOs). After side-stream, the amount of DNPAOs accounted for 84% of the total PAOs, the removal rate of TN rising from 51.1% to 61.1%, the removal rate of TP rising from 35.5% to 92.7% and there was no significant difference in COD, NH4+-N removal efficiency which was 74%,95%, respectively. In addition, the combined system achieved a markedly sludge reduction and solved the contradiction of solid retention time between nitrogen-and phosphorus-removal bacteria. The analysis on microbial community indicated that application of side stream system impacted heavily on microbial community structure and abundance. Denitrifying phosphorus removal species, Thauera spp. and Dechloromonas spp. in Betaproteobacteria group, increased to 9.0% and 8.5% of total bacteria, while Acinetobacter spp. in Gammaproteobacteria group decreased sharply from 8.9% to 1.2% in abundance. Therefore, combined side stream and A2O process was a better strategy to favor the enrichment of denitrifying phosphorus-accumulating organisms and achieve high and stable contaminants removal rate with sludge reduction in treating low carbon source municipal wastewater, confirming that the effluent reaches wastewater discharge standard level-A.