Research On Two-stage A/O Effluent Advanced Treatment Process In Pig Farms

Intensive breeding has produced a large amount of high COD and high NH₃-N farm sewage,which seriously pollutes the environment,and urgently needs efficient and low-cost pig farm sewage treatment technology and process.At present,Yangxiang company’s pig farm sewage mainly adopts two-stage A/O process,the pig farm sewage water quality treatment to COD 150-250mg/L,NH₃-N 20mg/L or so,its water quality can meet the farmland irrigation water quality standards,can be directly discharged to the supporting forest land of the pig farm.However,there is no supporting woodland near the pig farm in Yangxiang’s new building to absorb two-stage A/O effluent,so the two-stage A/O effluent of the pig farm should be deeply treated to the surface of Class 5 water directly discharged.However,at present,Yangxiang Company can only use biochemical+ultrafiltration+reverse osmosis process to treat pig sewage to surface five types of water,and the investment and treatment cost of water per ton of this process are high..How to meet the environmental protection requirements of surface five types of water and significantly reduce investment and treatment costs is a top priority.In this study,the combined process of coagulation precipitation,ozone/Fenton advanced oxidation and aeration biological filter was used to deeply treat the two-stage A/O effluent of the farm,and the optimal operating conditions of the combined process were determined,so that the water quality indicators such as COD,NH₃-N,and TP reached the standard of five types of surface water,which provided a new idea for the advanced treatment of wastewater in the farm.The main findings are as follows:（1）Exploration of optimal conditions for the treatment of pig farm sewage by coagulation processBy comparing the treatment effects of PFS and PAC on farm sewage,it was found that PFS had a good removal effect on farm sewage,and when the PFS dosage reached 0.3m L,the removal rates of COD and TP reached 66.4%and 96.7%,respectively.The pH value of sewage is also an important factor affecting the coagulation effect of PFS,and the coagulation effect of PFS is the best under neutral pH conditions,and the removal rates of COD and TP reach 62.9%and 98.6%,respectively.Flocculant PAM can aggregate floc particles with small molecular weight and dispersion to form large molecular weight and compact floc,when the amount of PAM is 0.3m L,PAM has the best coagulation effect,and the removal rates of COD and TP reach 66.4%and 99.3%,respectively.The main effect of stirring on the coagulation effect is to make the coagulant and the organic matter in the sewage,phosphate,etc.fully contact,so as to remove it by complexation and adsorption,when the stirring time is 90s,the coagulation effect is the best,the removal rate of COD and TP reaches 65.5%and 99.4%respectively.In this study,two main factors,PFS dosage and pH value,were selected for the response surface test,and the removal rate of COD and TP was used as the response value,and the final output was that when the PFS dosage was 0.35m L and the pH value was 7.2,the removal rate of COD and TP reached the maximum,66.7%and 99.8%,respectively.（2）Study on the oxidation efficiency of Fenton in pig farm sewage under different conditionspH is the main factor affecting the oxidation efficiency of Fenton,when the pH is3,Fenton oxidation effect is the best,COD,chromaticity,TP and TN removal rates are 55.2%,97.2%,77.2%and 33.2%,respectively.The molar ratio of Fe²⁺/H₂O₂is an important indicator for determining the amount of agent,and the removal effect is the best when the molar ratio is 1,and the removal rates of COD,chromaticity and TP reach 75.0%,96.3%and 90.9%,respectively.The removal effect of H₂O₂was best when the concentration was 0.5g/L,and the removal rates of COD and chromaticity were 68.9%and 96.3%.After many tests,it was found that the optimal time of the reaction was 30min,when the COD removal rate reached more than 60%and the chromaticity was reduced to less than 20 degrees.The three main factors of pH,Fe²⁺/H₂O₂molar ratio and H₂O₂dosage concentration were tested with COD removal rate as the response value,and the final output results were that when the H₂O₂dosage concentration,Fe²⁺/H₂O₂molar ratio and pH were 0.52g/L,1.07 and 3.01,respectively,the COD removal rate reached the maximum value of 75.3%.（3）Exploration of optimal conditions for ozone oxidation of sewageThere are three types of catalysts:activated carbon,metal oxide,activated carbon and mixture of metal oxide,and the catalytic effect of activated carbon is found to be the best through experiments,and the removal rates of COD,chromaticity and NH₃-N are 52%,97.5%and 51%,respectively.When the volume fraction of the catalyst is100%,ozone oxidation is the best,and the removal rates of COD,chromaticity and NH₃-N reach 58%,97.5%and 56.5%,respectively.When the ozone flow rate was1.5L/min,the removal rates of COD and chromaticity were 65.5%and 95%,respectively.When the pH of ozone oxidation reaction is 7-8,the COD removal rate reaches 66%;At the reaction time of 30min,COD has been reduced to 61mg/L,and the COD removal rate has reached 54%.The results showed that when the reaction time was 38min and the ozone flow rate was 1.6L/min,the removal rate of COD and NH₃-N reached a good effect,58.6%and 49%,respectively.（4）Exploration of the best process of aeration biological filterWhen the hydraulic residence time was 8h,the efficiency of BAF was better,and the removal rates of COD and NH₃-N were 65.5%and 87.6%,respectively.When the aeration amount was 0.2L/min,the treatment effect of BAF was better,and the removal rates of COD and NH₃-N were 54.3%and 87.7%.When the exposure-stop ratio was 1:1,the BAF treatment effect was good,COD removal rate reached 53.1%and NH₃-N removal rate reached 88.8%.BAF operates under the optimal conditions of each factor,and the COD of the effluent was stable≤40mg/L,and the NH₃-N was stable≤1.5mg/L.In summary,this study carried out the advanced treatment of coagulation precipitation,Ozone/Fenton oxidation and aeration biological filter combination process of the two-stage A/O effluent of the pig farm,so that the COD,NH₃-N and TP indicators have reached the requirements of surface five types of water,and this study provides a new idea and application reference for the advanced treatment of pig farm sewage to surface five types of water.