Analysis Of Influent Characteristics And Operation Stability In A WWTP And Solutions

This paper takes an A-A²O WWTP as the research object.The main research contents are divided into three aspects.Firstly,collecting the influent and effluent water quality data to study the change of major pollutants and its treatment stability;Secondly,monitoring pollutants'change along the path of A-A²O tank with the worst treatment effect and its operating conditions to study factors affecting nitrogen and phosphorus removal;Thirdly,running a pilot reactor to verify the influences of main influencing factors of nitrogen and phosphorus removal and furthermore provoiding feasible solutions.At the mean time,sludge production,chemical drug consumption,electric consumption and operation control parameters of A-A²O tank with the worst treatment effect were recorded.From 2013 to 2017,the influent SS,COD_cr,BOD₅ and TP showed a decreasing trend.However,the influent NH₄⁺-N and TN showed an increasing trend.The BOD₅/COD_crr ratio in the influent was stably around 0.51,so the biodegradability of wastewater was good.The COD_cr/TN ratio in the influent showed a decreasing trend year by year and this aggravated the reality of insufficient carbon source for denitrification.The average of COD_cr/TP ratio in the influent is 77.8 and is continuosly increasing.This ratio and its trend satisfy the requirement of biological phosphorus removal.The average removal rates of SS,COD_cr,BOD₅,NH₄⁺-N,TN and TP were97%,93%,97%,95%,76%and 96%respectively.Among them,the removal effect of SS,COD_crr and BOD₅ was stable,but the removal effect of NH₄⁺-N,TN and TP deteriorated with the operating life of the WWTP.The SS,COD_cr,BOD₅,NH₄⁺-N,TN and TP in the influent varied month from month and it was mainly caused by the rainfall and the variation of citizen's life style within a year.The SS,COD_cr,BOD₅,NH₄⁺-N,TN and TP also varied from hour to hour in one day and it was mainly due to citizen's daily time table.According to the inffluent and effluent data of the worst effective one of the four A-A²O reactors in 2017,the average removal rate of NH₄⁺-N was 93.1%and the average removal rate of TN was 71.2%.The average nitrification rate of aerobic zone of this A-A²O reactor was0.1092g NH₄⁺-N/?gVSS·d?in both Febrary and March,2017 and was 0.1228g NH₄⁺-N/?gVSS·d?in August,2017.The average denitrification rate of A-A²O tank was 0.0469g NO_x^--N/?gVSS·d?in both Febrary and March,2017 and was 0.0658g NO_x^--N/?gVSS·d?in August,2017.The main factors affecting the nitrification and the denitrification are deemed to be insufficient oxygen feeding rate of aerobic zone and insufficient carbon source of anoxic zone respectively after checking factors which might affect nitrification and denitrification and then verified by pilot test.The suggested solutions are to replace the air diffusers of aerobic zone and use a part of the effluent of primary sedimentation tank as carbon source for denitrification of anoxic zone.The pilot test results indicated that the reasonable influent flowrate ratio of pre-denitrification zone to anoxic zone is 5:3.The average removal rate of TP was 95.1%in 2017 and there were altogather 10 days of effluent TP exceeding the discharge standard in this year.Therfore,A-A²O combined with chemical dephosphorization can stably remove phosphorus.It was unexpected that TP was mainly removed by denitrifying phosphorus removal in anoxic znoe according to the monitored results of TP in each znoe of A-A²O reactor and the average rate of absorbing phosphorus in A-A²O reactor was 0.0376g TP/?gVSS·d?in December,2017.