Optimization Study On The Nitrogen And Phosphorus Removal Of Modified Two-sludge System Under The Condition Of Low Carbon Source

In recent years, the phenomenon of eutrophication still presents a rising trend because of excess discharge of nitrogen（N） and phosphorus（P） in sewage and industrial wastewater. So how to control the N, P level is still important in the study of the current water environment. The current sewage treatment plants mostly adopt the traditional biological nitrogen and phosphorus removal processes, and these processes can achieve better effect on nitrogen and phosphorus removal under the condition of enough carbon source. However, most of urban sewage in China is lack of carbon source, and sewage treatment plants need to add another carbon source to achieve better nitrogen and phosphorus removal, which further increases the operation cost of sewage treatment plant. Therefore, this research improved the traditional two-sludge system（A₂NSBR）, and compared with the traditional multi-stage anaerobic-aerobic-anoxic system（multi-stage SBR）, to explore the modified process of nitrogen and phosphorus removal efficiency, then further researched the utilization efficiency of the carbon source of modified two-sludge system.The whole experiment was divided into two stages（stage I and stage II）. Stage I was to explore the method of resolving insufficient carbon source in urban sewage, which compared and analyzed nitrogen and phosphorus removal（NPR） effect between modified two-sludge system and traditional anaerobic-aerobic-anoxic process under the condition of low carbon source wastewater. The modified two-sludge system was experimental reactor, which was optimized by adding two stages of micro-aeration（aeration rate 0.5 L$min-1） in the anoxic period of original two-sludge system, and multi-stage anaerobic-aerobic-anoxic SBR was the control reactor. When the influent COD, ammonia nitrogen, SOP concentration were 200, 35, 10 mg$L-1, the NPR effect of experimental reactor was better than control reactor with a removal efficiency of TN 94.8% vs 60.9%, TP 96.5% vs 75%, respectively. The effluent SOP, ammonia, TN concentration of experimental reactor were 0.35, 0.50, 1.82 mg$L-1, which could fully meet the first class of A standard of the Pollutants Emission Standard of Urban Wastewater Treatment Firm（GB 18918-2002）. Using the optimized treatment process, the largest amount of nitrogen and phosphorus removal per unit carbon source（as COD） were 0.17 g N$g-1 and 0.048 g P$g-1 respectively, which could furthest solve the lower carbon concentration in today%s municipal wastewater.Stage II studied the utilization efficiency of the carbon source of modified two-sludge system. on the basis of experimental reactor of stage I, this stage further optimized the process to research the NPR and the utilization efficiency of the carbon source when the influent COD, ammonia nitrogen, SOP concentration were 200, 50, 15 mg$L-1. The results showed that through continuous optimization of process, NPR of R1, R2, R3 and R4 stages became better and better, and R3 was the best. The system could achieve TP removal amount of 12.45 mg$L-1（removal rate 80.3%） and TN removal amount of 45.20 mg$L-1（removal rate 90.4%）. Modified two-sludge system could achieve 0.062 g P$g-1COD and 0.226 g N$g-1COD removal.So, the modified two-sludge system could greatly improve the utilization efficiency of carbon source, which has great reference value for the treatment of low carbon source wastewater in the practical application.