Strengthening Measures For Treatment Of Swine Wastewater In Multistage AO Process

At present,most pig farms use multi-stage AO process to treat swine wastewater in China.However,the characteristics of high pollutant concentration and high SS of swine wastewater make it very difficult to deal by multi-stage AO process,and the nitrogen and phosphorus in effluent can’t meet the discharge substandard.Based on the multi-stage AO process,this study investigated the effect of pre-aeration+initial precipitation,multi-stage water intake and post dephosphorization on the treatment of swine wastewater.Meanwhile,the effect of denitrification by adding carbon source to improve the alkalinity was investigated,so as to enhance the removal effect of ammonia nitrogen in the nitrification process.At the same time,to remove some pollu tants in the pretreatment section,improve the biodegradability of wastewater and eventually reduce the pressure of multi-stage AO process,the pretreatment method of dry collection swine wastewater was optimized.The effect of pre-aeration+initial precipitation,multi-stage water intake,chemical phosphorus removal and other strengthening measures was investigated by pilot test.The results showed that the optimized operational conditions were pre-aeration time of 18 h,aeration rate of 0.8 m³/（m³·h）air,precipitation time of 30 min,inflow volume ratio of 9:1,ferrous sulfate dosing quantity of 1.66,respectively.The effluent COD,NH₄⁺-N and TP concentration was about 230,94,7 mg/L,but using these strengthening measures couldn’t make ammonia nitrogen meet standard.The main reason of not reaching the standard of ammonia nitrogen is that the alkalinity of nitrification process is insufficient.However,the cost of dosing alkali directly is too high.Therefore,adding carbon source to increase the alkalinity in the denitrification process was investigated,so that the removal of ammonia nitrogen in the nitrification process can be indirectly improved.In this section,carbon sources were extracted from cheap and easily available flour and cassava residue powder with high starch content.The denitrification rules of enzymatic hydrolysate of flour and cassava residue powder with methanol,glucose and sodium acetate as carbon sources were studied by batch denitrification test.Flour enzymatic hydrolysate and sodium acetate were selected as the additional carbon sources of multi-stage AO process.The continuous dynamic test results showed that the strengthening effect of sodium acetate as carbon source on the multi-stage AO process was better than that of the flour enzymatic hydrolysis solution.When sodium acetate selected as carbon source,the COD,NH₄⁺-N and TP concentrations in the effluent were 290,25 and5 mg/L respectively and the effluent could reach the standard stably.The pretreatment effect of hydrolytic acidification with crystallization precipitation method on dry and dry collection swine wastewater was investigated through pilot test.The operation parameters of hydrolytic acidification reactor were optimized and the optimal reaction conditions of hydrolytic acidification solution by crystallization precipitation method were studied.The results showed that the optimized operational conditions of hydrolysis acidification reactor were HRT of 8 h,initial pH of 7;the optimized reaction condition s of crystallization precipitation method were pH of 9,Mg/P=1:1,reaction time of 40 min.After pretreatment,the COD,TP and SS could be removed by 23.4%,48.8%and 16.1%respectively.VFA content could be increased by 58.7%and B/C could be increased from 36.4%to 54.7%.