Study On Anaerobic-aerobic Treatment Process Of Swine Wastewater Based On Organic Matter Capture

As the scale of swine breeding increased,manure and urine sewage（swine wastewater）is concentrated in local areas and has become the main source of pollutants in some areas.In areas with limited land,the anaerobic-aerobic combined process is an alternative for swine wastewater.According to the previous research of our team,an anaerobic-aerobic combined process based on the separation of low content liquid and high content liquid was proposed,that was,the raw wastewater was divided into low content liquid and high content liquid through gravity sedimentation.The high content liquid was treated by anaerobic digestion,then digested effluent and the low content liquid were treated by aerobic unit.This technology can not only improve the efficiency of anaerobic digestion and biogas production,but also ensure the effect of aerobic treatment of digested effluent.However,due to the insufficient efficiency of gravity sedimentation of separation,a lot of organic matter remains in the low content liquid after separation,so the biogas production in the anaerobic digestion unit would be reduced.Aiming at the problem of low separation efficiency,this paper proposed an anaerobic-aerobic combined treatment process based on organic matter capture.It was planned to improve the separation effect of gravity sedimentation through the backflow of aerobic sludge.Then,the effect of sludge culture and the capture of organic matter were studied.（1）The backflow sludge can only be returned from the aerobic stage.Therefore,the effect of influent COD/N ratio on the performance of partial nitrification and capture of pollutants were studied.As the influent COD/N ratio increased from 1.66 to 5.26 and 8.93,the ammonia removal efficiency increased from 60%to 90%,and the nitrosation efficiency decreases from 97%to 85.7%and 71.9%.The low nitrosation efficiency was not conducive to match subsequent anaerobic ammonia oxidation.Compared with the control（without addition of aerobic sludge）,the addition of aerobic sludge obviously increased the COD capture capacity,with a removal efficiency increasing by 15-20 percentage points,and the adsorption capacity increasing by 12-16%.However,the COD capture effect of different sludges was relatively small,with the removal efficiency being less than 5 percentage points,and the adsorption capacity being less than 4%.Consideration of factors such as organic matter capture,partial nitrification,and nitrosation efficiency,the low COD/N ratio was more suitable as partial nitrification stage influent and the cultivation of aerobic sludge for pollutant capture.（2）The effect of sludge backflow ratio on the separation of pollutants was investigated.The separation effect of NH₃,TN,and TP increased with the increase of the sludge backflow ratio,and the separation effect of COD was best when the backflow ratio was 30%.At this time,the separation factor was 0.443 and the recovery rate was 71.8%.Considering the volume and TS concentration of high content liquid,the separation effect of organic matter,the suitable backflow ratio of sludge was 30%.（3）The effect of sedimentation time on the separation of pollutants was studied.The addition of sludge would slow down the sedimentation velocity of swine wastewater.To reduce the volume of the high content liquid to 30-40%of the raw wastewater,the sedimentation time would be at least 2 hours.At 4 h,the removal efficiency of COD was 73.8%,the recovery efficiency was 78.4%,and the separation factor was 0.451.Therefore,in order to achieve a suitable separation effect,the sedimentation time would reach 3-4 h.（4）The effect of adding aerobic sludge on anaerobic digestion was researched and the new process was economically analyzed.The volume of the high content liquid without and with adding sludge was15.2%and 26.1%of the raw wastewater,respectively,and the biogas output accounts for 76.5%and 91.7%of the total biogas output.The anaerobic digestion temperature of the high content liquid could be increased 33°C and 22°C by the waste heat of biogas power generation.In addition,the backflow sludge neither promotes nor inhibits the anaerobic digestion of swine wastewater.The addition of sludge increased the investment cost of the new process by about 2%,but the biogas production increased by24.1%.It can reduce the production of aerobic sludge,so the total operating cost had been decreased by41.6%.