Experimental Study On Inverted A~2/O Process For Treatment Of Domestic Sewage In Villages And Towns

In recent years,with the development of the economy and the improvement of people’s living standards,the discharge of domestic wastewater in villages and towns has continued to increase,but the construction of corresponding sewage treatment plants has not kept up with the pace of economic development,resulting in serious pollution of nearby rivers and lakes and eutrophication of water bodies.The phenomenon is not uncommon.Therefore,it is urgent to take action to explore suitable treatment processes for domestic sewage in villages and towns to control the water environment pollution in the vast villages and towns.In order to solve the problem of water pollution in villages and towns,this experiment uses an inverted A²/O bioreactor to treat domestic sewage in Sichuan villages and towns.The water used in this experiment is sewage from a village and town in Sichuan.The sludge is cultivated and domesticated in the form of inoculated sludge first;then orthogonal experiments are used to investigate the removal of COD,TN,NH₄⁺-N and TP and other conventional water quality indicators.Taking the removal effect of nitrogen and phosphorus as the key research object,the optimal operating parameters of the inverted A²/O under different test conditions are screened out;after the optimal operating conditions are determined,the repeatability test analysis is carried out to study the inverted A²/O The stable removal effect of various pollutants under continuous flow,the processing performance of each structure unit and the material balance relationship of C,N,P flow in the inverted A²/O system;optimization through the combination of biological phosphorus removal and chemical phosphorus removal（FeSO₄）Measures to conduct enhanced research on TP-compliant emissions.The results showed that:（1）During the sludge domestication period,the inverted A²/O system has stable treatment effects on COD,TN,NH₄⁺-N,and TP,and the average effluent concentrations of the corresponding water quality indicators are 36 mg/L,14.12 mg/L,4.28 mg/L and1.22mg/L respectively,the average removal rate is 85.3%,61.7%,84.6%and 64.8%respectively.Only the effluent concentration of TP cannot reach the first grade A standard（≤0.5mg/L）,and the total time from sludge debugging to stable operation 30d.（2）Through the orthogonal test,comprehensively analyze the removal effect of hydraulic retention time,sludge reflux ratio and water-gas ratio on COD,NH₄⁺-N,TN,TP,and analyze that the optimal working condition hydraulic retention time is 10 h.The mud return ratio is 100%,and the water-to-air ratio is 1:15.（3）Repeatability test under optimal working conditions and stable operating conditions,the inverted A²/O process has a good treatment effect on various pollutants in the sewage of Sichuan villages and towns.COD,TN,NH₄⁺-N,TP,SS The effluent concentrations are 31 mg/L,14.64 mg/L,3.37 mg/L,0.89 mg/L,16 mg/L,and the effluent concentration of COD,NH₄⁺-N and TN is better than the first grade A standard of urban sewage,the effluent concentration of TP,SS can only reach the first level B standard;according to the analysis of the processing capacity of each processing unit,the reduction percentage of COD concentration in the hypoxia reaction section is 62.2%,the concentration reduction percentage of NH₄⁺-N is 66.2%,and the concentration reduction percentage of TN is 40%,the decrease percentage of COD concentration in the anaerobic reaction section is 13.9%,the decrease percentage of TN concentration is11.4%,the decrease percentage of COD concentration in the aerobic reaction section is6.0%,the concentration decrease percentage of NH₄⁺-N is 29.9%,TN The decrease percentage of TP concentration is 6.8%,and the decrease percentage of TP concentration is more than 80%.Through the analysis of the material balance formula of the inverted A²/O nitrogen and phosphorus removal process,the COD balance rate reaches 102.7%,and the nitrogen balance rate reaches 96.3%,and the balance rate of phosphorus reached 89.3%.A better understanding of the utilization distribution of C,N,and P by the inverted A²/O process,which provides theoretical reference value for evaluating the validity of experimental data,establishing mathematical models,and practical engineering applications of the inverted A²/O process.（4）In the combined experiment of biological phosphorus removal and chemical phosphorus removal,with the increase of the initial concentration of FeSO₄,the effluent concentration of TP gradually decreases.When the dosage of FeSO₄ increases to7.5mg/L,the TP effluent has reached the level A standard of urban sewage;the removal rate of TP increases with the initial ferrous iron The concentration increases slowly.When the dosage of FeSO₄ is greater than 10mg/L,the effluent concentration of TP does not change much;from the point of view of the choice of dosage position,it is compared with the alkalinity produced by denitrification to increase the ferrous iron In terms of the simultaneous oxidation rate,the TP removal effect obtained by adding FeSO₄ at the inlet of the aerobic tank is better;in the actual continuous operating condition operation test,the average effluent concentration of TP is 0.33mg/L,compared with In order to increase the average removal rate by 11%before the addition of the agent,the addition of FeSO₄ has a slight promotion effect on the SS effluent,so that the p H of the effluent is slightly reduced,but it does not affect the biological activity of the activated sludge;in terms of economic cost,the investment The cost of medicament for adding FeSO₄ is about 0.0075 yuan/t,and it is more economical to choose to add FeSO₄.