| Eutrophication problem is more and more serious nowadays because of Nitrogenand Phosphorus excessive discharge.With the enhancement of environment protectconsciousness and GB18918-2002implement,no matter new-build WastewaterTreatment Plants or existing ones are facing the challenge of depth Nitrogen andPhosphorus removal problem.Orbal oxidation ditch is a new technology of oxidationditch which composed by3concentric oval-shaped ditch.Its unique structure andoperating mechanism make it gain more stable treatment effect with moreenergy-efficient way.However,due to the lack of anaerobic environment wherebiological phosphorus release occurs,the removal of phosphorus in Orbal oxidationditch is not ideal.Addition an anaerobic pond in front of the oxidation ditch system cancompensate for the deficiencies of its biological phosphorus removal,then an improvedOrbal oxidation ditch process with simultaneous denitrification and phosphorus removalfunction is formed.The pre-anaerobic tank Orbal oxidation ditch process is used in a wastewatertreatment plant in Chongqing, and a chemical phosphorus removal technology isassisted after the biological treatment systems in this plant. However, due to receive alarge number of industrial wastewater, as well as the problems in the runningregulation,the plant can not achieve stable removal on nitrogen and phosphorus.Afetrthe analysis of the plant’s historical and statistical data and a series of field tests,thestudy found the reasons for poor effect of nitrogen and phosphorus removal,andproposed a set of improving programs.After the adjustment of the aeration operationmode, the operating conditions of the plant is significantly improved.The study analyzed the statistics of the plant’s influent and effluent in2010,resultsshow that the oxidation ditch system has a good removal efficiency on COD andammonia, removal rates were (92±7)%and (92.7±8)%,but the TN and TP removalefficiency is poor: There was a rate of7%in effluent TN concentration which excessedthe standard and a rate of31%which was approaching to effluent limits; Effluent TPconcentration had a12%rate beyond the effluent standard,and had a48.5%rate beyond1.0mg/L under assisted chemical phosphorus removal technology.Through the analysisof field tests,the study believes that the main reasons for poor effect on nitrogen andphosphorus removal are influent quality and quantity beyond design value and volatile,industrial wastewater’s toxicity to active sludge and overlength on anaerobicretention time.In order to improve the stability on denitrification and phosphorus removal,thefollowing operation strategies are put forward:①Adjusting the aeration operationmode of the oxidation ditch so as to make the amount of oxygen in outer ditch up to50%of total oxygen, at the same time, strengthening the control of the returned sludgeratio and the dissolved oxygen in secondary sedimentation tank.②Strengthening theanalysis for the laboratory sampling data、field testing with portable instrument、microscopic analysis of activated sludge to collect the operation data.③Improving thereturned sludge flow、shuting down the influent gate、obtaining the influent qualitytimely and taking corresponding emergency measures to ease the shock to the activatedsludge by industrial wastewater.The rate of volatile activated sludge in the system had increased notably when theoperation mode of oxidation ditch was adjusted to A2/O．MLVSS/MLSS=0.57±0.02，which were8.8%higher than the same period of last year and14.0%higher than amonth ago．TN removal also had significantly increased, the removal rate was（65.8±7.0）%after the operation mode was adjusted,while the same period of last yearand last month were respectively59.5%and60.7%. The system maintains highbiological phosphorus removal efficiency after the operation mode was adjusted,biological phosphorus removal rates was74%,and it was71.2%before adjustment,bothare in high level,but chemical phosphorus removal rate was only8.2%．The analysisbelieve that，improper pH，lack of well-mixed reaction conditions，and improperphosphorus removal agent could be the reason of low chemical phosphorus removalrate．... |
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