Research On Low-carbon Sources Sewage Treated With Phostrip-step-feed SBR Process

With the trend of increased water eutrophication, discharge standard of nitrogen and phosphorus in municipal wastewater treatment plant becomes more and more strict and also it becomes more and more important to guarantee the effect of nitrogen and phosphorus removal. But organics concentration of municipal sewage in some cities or areas is becoming lower and lower and the COD/TN keeps decreasing, how to increase nitrogen and phosphorus removal effect in municipal sewage with low carbon-nitrogen ratio has become difficult problems. For the serious shortage of carbon source and difficulty of simultaneous nitrogen and phosphorus removal in low-carbon source municipal sewage, a new combined process of step-feed SBR combined with side stream phosphorus removal technique by external recycle of sludge is used to enhance the biological effects of nitrogen and phosphorus removal by rationalizing the distribution of carbon source in sewage and limiting aeration amount in order to reduce the invalid or excessive aerobic consumption of organic carbon source. The research used low-carbon source municipal sewage (COD/TN=4.22~6.23) as the object of study to investigate nitrogen and phosphorus removal effect of SF-SBR and P-SF-SBR process with long sludge age at different aeration amount level.The experimental results show that:①When aeration amount of the system is at a low level(about 3.57 m3/h·m3), step-feed SBR process has a better nitrogen removal effect than traditional one-step feed SBR.When the COD concentration of influent is below 200mg/L and average C-N ratio is 4.4, the removal efficiency of COD, NH3-N,TN is respectively 86.3%,95.7% and 66.3% in SF-SBR system with tow-step feed mode. Under the same level of aeration amount the removal percentage of COD, NH3-N,TN is respectively 91.8%,79.2% and 51.4% in the traditional one-step feed SBR system.②The aeration amount has influence on the effect of nitrification and denitrification of SF-SBR system:When the aeration amount is too low and DO concentration of the reactor is always below 0.2mg/L, the nitrification effect of the system is very poor and the effluent has high concentration of NH3-N and TN; When the aeration amount is too high so that DO concentration rises greatly at end of aerobic stage, the nitrification effect is good but denitrification effect is poor and the concentration of NH3-N is almost 0 mg/L but the concentration of TN is high. ③When the aeration amount is 3.57 m3/h·m3, the feed mode has influence on the effect of pollutants removal in SF-SBR system:When under equivalent tow-step feed mode, the removal efficiency of COD, NH3-N, TN and TP is respectively 78.8%,87.5%,57.5% and 13.6%;When under reduced tow-step feed mode, the removal percentage of COD, NH3-N,TN and TP is respectively 86.3%,95.7%,66.3% and 31.9%.④When the influent COD<200mg/L, C/N is 3.9, C/P is 25.9, controlling of the aeration amount for 3.57m3/h.m3 and SRT for 80d, the average removal efficiency of COD, NH3-N, TN and TP in P-SF-SBR system with tow-step feed mode is respectively 87.5%, 99.1%, 63.0%, 93.2%,and effluent water qualities reach first-degree A standards of《Letting Standards of Town Sewage Treatment Plant》(GB18918-2002).⑤When the influent COD concentration decreased further with C/N for 2.9 and C/P for 20.2, controlling of the aeration amount for 3.57m3/h.m3 and SRT for 80d, the average removal efficiency of COD, NH3-N, TN and TP in P-SF-SBR system with three-step feed mode is respectively 83.1%, 97.4%, 65.1%, 93.7%, and effluent water qualities reach first-degree A standards of《Letting Standards of Town Sewage Treatment Plant》(GB18918-2002).⑥The aeration amount has influence on the effect of phosphorus removal in P-SF-SBR system:When the aeration amount is at or below 3.57m3/h.m3, the system has a good efficiency of phosphorus removal and the phosphorus concentration of effluent water is always below 0.5mg/L; When the aeration amount is above 3.57m3/h.m3, the efficiency of phosphorus removal unstable and the phosphorus concentration of effluent water is in fluctuation.