Study On Strategies Of Biological Nitrogen Removal Process Operation Of WWTP

Along with the rapid development of social economy,environmental problems become more and more serious.One of the effective solutions to protect water environment is promoting the wastewater control and treatment.A WWTP of Shanxi province adopts SBR process(1# plant)and A~2 O process(2# plant).In order to stably satisfy the class A limit of grade one standard of the “Discharge standard of pollutants for municipal wastewater treatment plant(GB18918-2002)”,this study carried on several onsite tests to solve the problems encountered in the practical biological nitrogen removal operation.The factors influencing biological nitrogen removal effects were investigated by monitoring the water quality at different sites along the wastewater flow in the full scale biochemical reactor of the modified A~2 O process.The treatment of the mixture of the lysate resulted from the low temperature pyrolysis of residual activity sludge wasted by this WWTP and the municipal wastewater was tested.The onsites monitoring of the DO of a full scale biochemical reactor of a SBR system provided the first hand information data about the aeration effects of WWTP biological reactor.Right on the basis of this information,the inhibiting mechanism of the aerobic nitrification was analysed.By monitoring the water quality at different sites along the wastewater flow in the full scale biochemical reactor of the modified A~2 O process,it was discovered that: The removed TN fell only between 0.55 and 4.77mg/L from the inlet of the selection zone to the outlet of the anoxic zone.The removed NO3--N in the anoxic zone is equivalent to the amount of NO3--N contained in the returned nitrate mixture.BOD5/TN decreased along the wastewater flow in the anoxic zone indicating the dearth of the organic carbon source in the next half of the anoxic zone.When the lysate to the municipal wastewater ratio was 0.1‰ for the influent,the reactor ran regularly.The effluent CODCr and NH4+-N could all achieve the standard.With the lysate to the municipal wastewater ratio increased from 0.5‰ to 1.6‰ and finally to 1.75‰,the effluent CODCr and MLSS of the reactor increased gradually.The CODCr removal rate decreased and finally to 89.7%.The effluent NH4+-N did not show apparent change.When the lysate was added in the fixed ratio of 1.75‰,the effluent CODCr and the MLSS of the reactor also increased gradually.The CODCr removal rate decreased and finally to 91.0%.The effluent NH4+-N did not show apparent change.The effluent CODCr and NH4+-H of both the gradually lysate adding ratio reactor and fixed lysate adding ration reactor achieved the standards.With the lysate adding ratio was 1.75‰,the operation of the No.2 plant of this WWTP ran regularly.At this adding ratio,all the lysate resulted from the low temperature pyrolysis of residual activity sludge wasted by this WWTP could be treated.Therefore,the lysate can be treated by this way at the adding ratio of 1.75‰.Since the test was conducted in the winter,the temperature was low and the influent CODCr and NH4+-N were high,the treatment effects were affected.In addition,the lysate adding operation could cause bubbles which need to be controlled.The real time monitoring of the DO during the aeration,post-stirring and sedimentation period in one treatment cycle in a biochemical reactor of the SBR system in No.1 plant demonstrated that: According to the change of DO,the aeration procedure could be divided into three periods.The first period characterized with the intense and rapid DO fluctuation and the oxygen supply rate was approximately equivalent to the oxygen utilization rate.The average DO remained stable despite of the DO fluctuation.The DO during the end of the aeration procedure was high therefore it cost relatively long time to enter the anoxic procedure.Unfortunately,the anoxic state lasted only 4 min before the sedimentation procedure started.The post stirring procedure should be prolonged on the basis of reducing the aeration flow rate.The SOUR of the active sludge of No.1 plant was 3.70mg/(g·h)which was far more lower than it should be.The main reasons were surplus aeration,low BOD-sludge loading and insufficient sludge waste.The problem needed to be resolved by taking effective methods.