The Simultaneous Nitrification And Denitrifying Phosphorus And Nitrogen Removal In Continuous Flow Reactor With Intermittent Aeration

Eutrophication referred to the phenomenon that algae propagate in water and dissolved oxygen in water was consumed continuously,leading to the death of aquatic organisms such as fishes.A²/O process was a common sewage treatment plant process,and it was widely used because of its advantages such as simultaneous nitrogen and phosphorus removal,low bulking sludge and short total hydraulic retention time?HRT?.In recent years,there were many problems in the operation of A²/O process.Therefore,it was of great significance to upgrade the traditional A²/O process.In this study,intermittent aeration was used to treat domestic sewage by simultaneous nitrification and denitrifying phosphorus and nitrogen removal.In the anaerobic phase,denitrifying phosphorus accumulating bacteria released phosphorus into the sewage and absorbed volatile fatty acids to synthesize internal carbon source?PHB?.In the aerobic stage,the aerobic/anoxic alternating environment produced by intermittent aeration made the process of nitrification and denitrifying phosphorus accumulation happened simultaneously.The nitrogen and phosphorus were removed simultaneously in the way of"One carbon for dual purpose".The process combined simultaneous nitrification and denitrification with denitrifying phosphorus removal,without setting anoxic stage and nitrifying liquid reflux.Intermittent aeration instead of continuous aeration could save aeration energy consumption,and the effluent water quality was obviously improved.This paper mainly focused on how to start up simultaneous nitrification and denitrifying phosphorus and nitrogen removal process in A²/O reactor,optimizing working conditions and operation strategy,etc.The main research results were stated as follows:?1?Simultaneous nitrification and denitrifying phosphorus and nitrogen removal process was successfully started up by intermittent aeration.The start-up strategy was as follows:the domestic sewage was treated in A²/O reactor,the average influent COD?NH₄⁺-N?TN and PO₄^3--P concentrations were 259.34,60.26,64.42 and 6.10mg·L^-1,respectively.The anaerobic compartments were kept at 3,the anoxic compartments were reduced from 2 to 0,and the aerobic compartments were gradually increased from 5 to 7.Continuous aeration was used in the aerobic compartments in Run1,and intermittent aeration was used in the aerobic compartments in Run2^Run4,and the ratio of aeration to non-aeration was 40min/20min,40min/30min,and 40min/40min,respectively.The refluxing ratio of nitrification decreased from 150%to 0%.In Run4,the average effluent concentrations of COD,NH₄⁺-N,TN and PO₄^3--P were 26.40,1.03,5.84,0.30mg·L^-1,respectively.The removal amounts of nitrogen in the reactor increased from 192.30mg·h^-11 in Run1 to 244.00mg·h^-11 in Run4,and the corresponding removal rate increased from 65.40%to 95.30%.The activity of denitrifying phosphorus accumulation bacteria increased from 36.05%and 38.20%in Run1 to 140.50%and 133.40%in Run4,respectively.?2?After the system was started up successfully,the volume ratio of anaerobic and aerobic compartments was maintained at 3:7.The temperature was kept at 20²5?,the HRT was 15 h,and the ratio of aeration to non-aeration in the aerobic compartments was40min/40min.The effects of different aeration rates?150,120,100,80 and 60L/h?on simultaneous nitrification and denitrifying phosphorus removal were investigated.Under different aeration rates,the average effluent COD concentration was less than 34.00 mg/L,the removal rate was more than 86.10%;the average effluent PO₄^3--P concentrations were less than 0.46 mg/L,and the removal rate was more than 87.25%.When the aeration rate increased from 100 to 150L/h,the TN removal rate decreased from 90.30%to 74.20%.When the aeration rate decreased to 60L/h,the removal rate of TN increased to 91.20%.When the aeration rate was controlled at 60L/h,the removal efficiency of pollutants in the reactor was the best and the denitrifying phosphorus accumulation rate was up to 0.69mg·?g·h?^-1,the aerobic phosphorus uptake rate was only 0.14mg·?g·h?^-1.?3?The ratio of aeration to non-aeration was an important parameter to the intermittent aeration reactor.The study on the treatment efficiency of the reactor under different ratios of aeration to non-aeration can provide a reference for the practical engineering application.The HRT was 15 h,the volume ratio of anaerobic and aerobic cells was 3:7,the aeration rate was controlled at 60 L/h.The aeration/non-aeration ratio was controlled at 40min/40min,40min/30min,40min/20min and 40min/10min,respectively.Effect of different aeration/non-aeration ratios on COD and NH₄⁺-N removal was neglected.The average effluent COD and NH₄⁺-N concentrations were 31.02 and 1.60 mg/L respectively.When the first three ratios of aeration to non-aeration were used,the average effluent TN concentration was lower than7.50 mg/L,and the average effluent PO₄^3--P concentration was less than 0.42 mg/L.When the the fourth ratio of aeration to non-aeration was used,the average effluent TN and PO₄^3--P concentrations were increased to 20.60 and 0.96 mg/L,respectively,indicating that the performance of process in the ratio of aeration to non-aeration of 40min/10min worsen.?4?In order to study the optimizing HRT,aeration rate was controlled at 60L/h,the ratio of aeration to non-aeration of 40min/20min was applied,when the HRT were 15,13,11,9 h,the performances of the process were investigated.When HRT was 15 h and 13 h respectively,the effluent TN concentrations were 7.30 and 7.80 mg/L,respectively.The effluent PO₄^3--P concentrations were 0.30 and 0.40 mg/L respectively.When HRT was reduced to 11 h,although NH₄⁺-N could be fully oxidized to NO₃^--N,the produced NO₃^--N could not be removed by denitrifying phosphorus removal because of the inhibition of phosphorus release,which led to the increase of effluent TN concentration to 17.20 mg/L;When HRT was reduced to 9 h,both anaerobic phosphorus release and nitrification were affected,the concentrations of NH₄⁺-N and TN in effluent were increased to 10.80 and 24.10mg/L,respectively.Perfect treatment efficiency was obtained when HRT was 15 and 13 h.However,when the HRT was 13h,the treatment load of the reactor was higher than that of 15h,which was more economical.?5?The reactor was operated at HRT of 13h,aeration rate of 60L/h,and the ratio of aeration to non-aeration of 40 min/20 min.The average COD,NH₄⁺-N and TN concentrations in the influent were increased to 410.00,90.00 and 92mg/L respectively,and the influent PO₄^3--P concentration was 6.1 mg/L.The ability of simultaneous nitrification and denitrifying phosphorus and nitrogen removal process resisting impact load was studied.The results showed that the process can resist the impact load of COD,and the removal efficiency of organic matter,nitrogen and phosphorus by the system under high COD load was not influenced.Under the high ammonium nitrogen load,the process could not operate stably,although the effluent COD and PO₄^3--P concentrations were still low.But the effluent concentration of NH₄⁺-N and TN reached 11.20 and 19.60 mg/L,respectively.?6?In order to make the reactor adapted to high NH₄⁺-N load,two control strategies of increasing aeration volume and HRT were adopted respectively,while keeping the ratio of aeration to non-aeration at 40min/20 min.After the aeration rate was gradually increased from60 to 100L/h,the NH₄⁺-N removal load of the reactor was increased,but the removal rate of TN was still low.The average effluent NH₄⁺-N and TN concentrations were 1.10 and 22.50mg/L.This is due to the imbalance between nitrification and denitrifying phosphorus removal after increasing aeration rate and the inhibition of anaerobic phosphorus release.Then controlling the aeration rate at 60 L/h and increasing HRT to 15 h,the average effluent COD,NH₄⁺-N,TN and PO₄^3--P concentrations were 32.00,0.34,12.20 and 0.37 mg/L,respectively,and their average removal rates were 88.94%,98.91%,87.91%and 87.26%,respectively.Prolonging HRT can enhance both nitrification and denitrifying phosphorus removal in aerobic stage at the same time,so it can served as a operation strategy for simultaneous nitrification and denitrifying phosphorus and nitrogen removal process in continuous flow reactor with intermittent aeration under higher NH₄⁺-N load.