Study On Regulation Of Modified A~2/O Process For Low C/N Municipal Wastewater Treatment

The low C/N ratio urban sewage as raw water and the modified A2/O press werestudied in this paper. The raw water get into anaerobic tank and anoxic tank respectively.These can allocate organic carbon for nitrogen and phosphorus removal reasonably. Theeffluent of both anaerobic and anoxic tank get into aerobic tank. The effluent of aerobictank get into secondary sedimentation tank. The mixed liquor of aerobic tank reflow inanoxic tank and the sludge of sedimentation tank reflow in anaerobic tank.The effect of COD and TP were very well in low temperature by the modified A2/Oprocess. But the effect of TN and NH4+-N were very bad. In higher sludge load, thereactor had taken place non-filamentous sludge bulking. The vorticella and nematodewere grown in activated sludge under low temperature.In modified A2/O process, the effect of different influent distribution of anaerobicand anoxic were2:1,1:1and1:2were studied. The result had indicated that the removalof COD and NH4+-N had hardly impact by the ratio of water allocation and the averageremoval rate was86.7%and97.03%. With the increasing of enter into anoxic tank, theremoval rate of TN were increased, but the removal rate of TP were reduced becauseshort of organic carbon. In a word, the effluent could meet to Grade A dischargingstandard of pollutants for municipal wastewater treatment plant (WWTP)(GB18918-2002) when the influent distribute of anaerobic and anoxic tank ratio by1:1,and the average effluent concentration of COD, NH4+-N, TN and TP was33.5mg/L,0.87mg/L,13.1mg/L and0.43mg/L. And it had appeared denitrifying phosphorusremoval in anoxic tank.The volume ratio of anaerobic, anoxic and aerobic tank had seldom effected forCOD and NH4+-N. With volume ratio of1:1:4, the sludge had taken the phosphorusmore and the sludge were aged, a lot of rotifer were grown. But for removal of TN, thebest of volume ratio was1:1:3and had well removal rate of nitrogen and phosphorus,and it average of removal rate was75.1%and93.3%, and the sludge performance verywell.The aerobic tank had adopted decrescent aeration mode. Denitrifying phosphorusremoval had occurred in anoxic tank when the system working regular, and the removalrate of TP were62.9%to65.2%in anaerobic tank. Part of TN had degraded in aerobictank that occurred simultaneous nitrification and denitrification. Different mixture return ratios have rare effect for COD, but for TN that average effluent concentrationwere14.5mg/L to12.3mg/L. This process had well nitrogen and phosphorus removal inmixture return ratios of200%. When the sludge return were50~75%, pollution cleaningwere very well.Under low load of sludge be bad for denitrification and phosphorus removal, andthe sludge were aged. When the system had high load of sludge, the sludge had takenplace the non-filamentous bacteria sludge bulking, and the SVI were more than200inaerobic tank. High DO concentration and addition industrial sewage be bad for theremoval effect of pollutant.