Pilot-scale Study On Deep Denitrification Of Wastewater By AOA Dynamic Nitrification And Denitrification

Generally,the influent carbon source of municipal wastewater treatment plants(MWWTP)in China is low,and the carbon-nitrogen ratio(C/N)can not meet the demand for denitrification,resulting in a low removal rate of total nitrogen(TN).To solve the above problems,provide optimization schemes against MWWTP dealing with low C/N domestic sewage,reduce sewage treatment costs and realize energy-saving and efficient deep nitrogen and carbon removal,this thesis carried out a pilot study on the treatment of low C/N domestic sewage by anaerobic/aerobic/anoxic(AOA)dynamic nitrification and denitrification process.The operation effects of the system in the treatment of low C/N domestic sewage under different influent loads,reflux ratio(R),temperature(T),external carbon source,and other parameters were discussed.The experiment was divided into two parts.AOA pilot plant took actual campus domestic sewage as the influent and had run for 264 days.The first part explored the pollutant removal performance of the AOA pilot plant during startup and domestication,stable operation,low load operation during holidays and recovery after school.These three periods had run for 177 days.In the second part,an 87-day parameter experiment was carried out.The results showed that in the first part of the experiment,the system could complete the domestication of nitrifying bacteria within one month under the condition around 20?.The effluent TN of the system decreased to 13.43 mg/L when T>25? and the shortest water retention time was 0.88d.During the campus holiday operation,the influent TN was 10?30 mg/L,and the average concentrations of TN,NH₄⁺-N,and COD in the effluent of the system could meet the standard.Within one week after the start of school,the influent TN increased sharply from 27.29 mg/L to72.4 mg/L,the denitrification effect of the system deteriorated,and the microorganisms were impacted by the high load influent,and the mixed liquid suspended sludge concentration(MLSS)decreased significantly.However,after one week,the effluent NH₄⁺-N was immediately restored to 1.96 mg/L,the effluent TN fell to 14.18 mg/L,and the sludge concentration also increased slowly.This showed that the system has a high ability to resist impact load.High MLSS,high nitrite accumulation rate(NAR),and higher temperature have positive impacts on the denitrification of the system,the maximum TN removal load of the device was 55.19g N/(m~3·d).In the second part,by comparing the effluent effects of R were 1:1,1:2,and 2:1,it can be found that the best effect was R of 1:1.The maximum simultaneous nitrification and denitrification(SND)rate and endogenous denitrification(ED)rate of three reflux ratios was R of 1:1.The analysis showed that reducing the reflux ratio led to the reduction of reflux sludge and the amount of COD_intra,which was a disadvantage to carbon storage.Increasing R accelerated the circulation speed of the mixed liquid,and shorted the contact time between sludge and sewage,which would bring adverse impact on the denitrification of the system.Adding an external carbon source to the anaerobic tank could increase the COD_intravalue,which was positively correlated with ED rate and TN removal rate in the anoxic section.Under a certain sludge concentration,the addition amount of external carbon source did not increase in proportion to the COD_intravalue.In this experiment,adding 50 mg COD/L composite external carbon source improved the effluent effect of low temperature(15?20?).Under the influent conditions of this experiment,the denitrification effect of the system at low temperatures could be improved by changing the operating parameters.Treatment effect of the AOA system improved by prolonging the hydraulic retention time(HRT)when T<25?.While 20?>T?15?,the denitrification effect in the anoxic section improved by adding an appropriate amount of carbon source,and the nitrification effect improved by prolonging the HRT in the aerobic section.15?>T?12?,the denitrification effect of the system deteriorated,but it still achieved excellent ammonia nitrogen and COD removal.The system could still restore efficient denitrification and carbon removal performance by raising the temperature.