Experimental Research Of Enhanced Biological Nitrogen And Phosphorus Removal Under A~2/O-BAF Two Sludge System

With the increasingly strict sewage discharge standard and the increasing annual discharge of municipal wastewater,China's municipal wastewater treatment is fecing the dual pressure of requirements in improving treatment efficiency and improving operating costs.The low C/N and low C/P characteristics of urban domestic sewage cause the low removal efficiency of nitrogen and phosphorus in current wastewater treatment plants,and there is contradiction and competition of sludge age and carbon source which is foremost reason on currently used single sludge system,and this made it is difficult to remove nitrogen and phosphorus synchronously and efficiently.Therefore,ensuring energy-saving on the basis of high-efficiency nitrogen and phosphorus removal is the key to alleviate the eutrophication of water bodies and ensure the sustainable development of wastewater treatment.The Anaerobic/anoxic/aerobic?A2/O?-Biological aerated filter?BAP?two sludge system consisting of A2/O activated sludge system and BAF bio film system in series was used in this project.A2/O process mainly completes phosphorus reKoval and denitrification in a short sludge residence time.BAF achieve a stable nitrification process in a long sludge residence time.The denitrifying phosphorus-accumulating bacteria was enriched in A2/O that can use the nitrate-nitrogen or nitrite-nitrogen as an electron acceptor refluxed from BAF to complete the anoxic phosphorus uptake.This can efficiently treat low C/N and low C/P urban sewage through "one-carbon dual-use".Through the optimization of working conditions,process control and statistical analysis,the energy saving on the basis of high-efficiency nitrogen and phosphorus removal of A2/O-BAF system is realized.It can provide experimental support and technical sustain for excellent treatment of tow C/N and tow C/P domestic sewage efficiently and economically.The main research results are as follows:?1?.Under the low temperature condition of 11-14?,the A2/O system sludge age is 12 d,the nitrification liquid reflux ratio is 200%,the sludge reflux ratio is 100%,by increasing HRT from 8h to 11h gradually,the activated sludge can adapt to the low temperature.The results showed that when the average influent concentrations of COD,NH4+-N,TN and PO43--P were 193.1,58.6,60.3 and 5.1 mg/L respectively,their effluent concentrations were 38.64,2.30,13.80 and 0.42 respectively,which achieved the first level A criteria specified in the discharge standard of pollutants for municipal wastewater treatment plant?GB18918-2002?.On this basis,the effects of aeration volume and effective filler height on BAF nitrification were investigated.It was found that when the aeration volume in BAF was controlled from 60 L/h to 100 L/h,the effluent NH4+-N concentration was less than 5.0 mg/L.The required effective packing height is 1.8 m and 1.0 m respectively.When the aeration rate is increased to 120 L/h,the gas-water flow impact causes the bio film to fall off,resulting in effluent N14+-N higher than 5.0 mg/L.The material balance and statistical analysis of the anoxic section of the A2/O-BAF system in stable operation showed that simultaneously removed ratio of PO43--P and NO3--N were between 0.47 and 1.75,standard deviation ratio of PO43--P and NO3--N were 1.20 and 0.29 respectively.?2?.Ammonium chloride?NH4Cl?and sodium dihydrogen phosphate?NaH2PO4?were added in influent to reduce the C/N and C/P,and the removal of pollutants in the system under different C/N and C/P conditions was investigated.It was found that when the C/N and C/P were reduced to 2.40 and 31.40 by adding 25?35 mg/L NH4Cl and 2 mg/L NaH2PO4 in influent,the system could maintain good nitrogen and phosphorus removal efficiency nitrogen.The average effluent COD,ammonia nitrogen,TN and TP concentrations were 38.70,3.50,14.73 and 0.46 mg/L respectively,while the sludge concentration was stable at 2400 mg/L and the SVI was maintained at 122 mL/g.The sludge disintegrated when the C/N and C/P was reducing,and then sludge concentration reduced to 1200?1400 mg/L,and the SVI reached to 135 mL/g.?3?.By changing the anaerobic/aloxic/aerobic volume ratio of the A2/O system to 3:5:2 and 2:6:2 to getting on active recovery of activated sludge stored for nearly two months,nitrogen and phosphorus removal performance of the system was studied.It was found that the two startup modes have little effect on the removal of COD and ammonia nitrogen,and the effluent of their concentrations can meet the requirements of Grade A.When anaerobic/anoxic/aerobic volume ratio was 3:5:2,it is helpful to recovr removal efficiency of TN and PO43-P.On the 4th day,the effluent PO43--P concentration was lower than 0.42 mg/L.The effluent TN concentration was 14.20 mg/L,and the average anaerobic phosphorus release reached 27.60 mg/L after seven day.When the ratio of anaerobic to anoxic to aerobic volume was 3:5:2,the sludge sedimentation performance is better,and the SVI was stable at 95?100 mL/g.?4?.The nitrosated BAF reactor was started up by artificially distributing water to acclimate the sludge,by natural biofilm method.After the nitrosation was stabilized,the reflux ratio of the nitrifying solution was gradually increased,and the A2/O and BAF systems were operated in series.The rapid start-up strategy of nitrosated BAF and the simultaneous removal ratio of nitrite nitrogen and phosphorus in nitrosated denitrifying phosphorus removal system were studied.It was found that the effluent nitrite nitrogen gradually increased from 7.5 mg/L to 43.1 mg/L,and the corresponding nitrite nitrogen accumulation rate increased from 62.5%to 94.3%.The effluent NO3--N concentration first increased slightly and then decreased,and finally remained at 3.2 mg/L.When the reflux ratio of nitrifying solution was 200%,the average concentration of TN in BAF effluent is 13.3mg/L,which mets the first-class A standard.Carrying out the material balance and normal distribution statistics for the anoxic section of the A²/O-BAF reactor after stable operation,It is concluded that the ?PO₄^3--P/?NO₃^--N was simultaneously removed between 1.2 and 2.2,the probability is 52%when the ratio of ?PO₄^3--P and ?NO₃^--N was 1.71,and the standard deviation was 0.14.