Research On Effect Of Nitrogen And Phosphorus Removal From Low C/N Wastewater By Inverted A~2/O-MBR Process

With the rapid growth of market economy,caused the water shortage is a growing problem to China.Therefore,municipal waste water treating and recycling is needed.Nitrogen and phosphorus removal is inefficient owing to shortage of the carbon sources,and the water is hard to reach the discharge standards in most cities of China.Aiming at the problem,the inverted A2/O-MBR process was used to treat the municipal wastewater of Shandong province,and the enhanced nitrogen and phosphorus removal from municipal wastewater with low C/N was studied.The components and biodegradability of the influent water in wastewater treatment plants was analyzed,and the condition of MBR expanded graphite was optimized by an orthogonal test method.The removal rate of COD,NH3-N,TN,TP and SS were investigated in the paper by a long time detection,especially the TN and TP.For the effluent quality did not meet the grade A of national discharge standard of GB18918-2002,taking the chemical-aid of removal process method for nitrogen and phosphorus. At the same time,the causations of contaminations and cleaning methods were summarized systemically,and focused on the influence of EPS and SMP on membrane fouling.The experiment showed that:(1)The wastewater quality was fluctuated wildly.The BOD5/TN was between4.5and5.5,the average of BOD5/TP and BOD5/COD was12.7and0.24,it was low C/N and biodegradability of sewage water,becase it was influenced by the rainy season and combined system of municipal wastewater.(2)Through analyzing the orthogonal test,the superior ranges of inverted A2/O-MBR process’s parameters were recommended.Considering the removal rate of TN and the conditions of membrane fouling,the optimum operation conditions were determined as follow:air/water ratio was25:1,sludge recycle ratio was250%and MLSS was7000to9000mg/L.(3)The inverted A2/O-MBR process was efficient in removal of COD,NH3-N,SS,TN and TP,they were satisfied to grade A of national discharge standard of GB18918-2002,it was better than traditional process。the TN and TP concentration in effluent was19mg/L and1.88mg/L,the effluent TP conforms to one-classB permitted criteria,do not meet A. (4)The removal efficiency of nitrogen and phosphorus in low C/N sewage disposal system usually is low,so choosing to feed carbon resource and chemical phosphorus int he process.When the NaAc and PFS dosage was75mg/L and25mg/L,both TN and TP of effluent could reach the standard.(5)Through the study of mechanism,the content of carbohydrate in EPS and SMP was74.5%and79.8%,this showed that carbohydrate has a larger effect towards membrane fouling than protein.(6)During the running process,transmembrane pressure ranged from0.003to0.048MPa. By controlling the gas flushing and water back flushing as daily maintenance online,the membrane specific flux growing by0.3L/(m2-h-kPa) and0.04L/(m2-h-kPa) espectively.Results showed the recovering ratio of flux highest was100%when the concentration of NaClO was500mg/L,showed that chemical cleaning can remove effectively reversible pollutants.