Study On The Effect Of Aerobic Unit And Sedimentation Unit On Sludge And Nitrogen Removal In Anoxic Unit In Continuous-flow Systems

Among the existing technologies of biological removal of nitrogen,biological process with anoxic and aerobic alternation is very economy.There is a close relationship between nitrification and denitrification in the biological nitrogen removal.Even if there were enough organic carbon sources in the influent,the residual nitrate nitrogen was more than ammonia nitrogen in the effluent,which indicated that denitrification was more susceptible than the nitrification,which leaded to unsatisfactory effect of nitrogen removal.In this paper,the characteristics of sludge in aerobic unit and before and after precipitation under different operating conditions were investigated in experimental anoxic-aerobic(A/O)system and anaerobic-anoxic-aerobic(A~2/O)system using synthetic wastewater,and the effects of sludge characteristics in aerobic and sedimentation unit on denitrification in anoxic unit were investigated in order to provide theoretical guidance for improving the efficiency of biological nitrogen removal in sewage.The main results of the study are as follows:(1)The denitrification effect of three dissolved oxygen(DO)levels[3.0-3.5mg/L(Ⅰstage),2.0-2.5mg/L(Ⅱstage),1.5-2.0mg/L(Ⅲstage)]in aerobic unit and three hydraulic detention time(HRT)levels[2.0h(Ⅳstage),2.5h(Ⅴstage)and 3.5h(Ⅵstage)]in sedimentation unit was studied in an A~2/O process.The results showed that the denitrification activity of the sludge in sedimentation unit were the highest and the denitrification in anoxic unit was the best when the DO of aerobic unit was 1.5-2.0mg/L and the HRT of sedimentation unit was 2.5h;the denitrification in sedimentation unit was supplied by both internal and external carbon sources,and activated sludge preferred to use external carbon sources;the denitrification of sludge in sedimentation unit was directly related to the denitrification in anoxic unit.(2)The characteristics and denitrification of activated sludge in the sedimentation unit of A/O and A~2/O process were investigated under the same operating conditions.The results showed that the residual PHB in aerobic unit of A/O process was higher than A~2/O process under the certain sludge loading;the denitrification activity of sludge in A/O process was higher than that in A/O process,and the nitrate reductase activity was1.08 times higher than that in A/O process;the effect of denitrification was affected by the high nitrate loading in the anoxic unit of the A/O process,which resulted from the simultaneous intake of mixed liquid and refluxed sludge,and The dual anoxic environment of the anaerobic and anoxic unit of the A~2/O process made the system have better denitrification.These results imply that,in the biological treatment system,the operating conditions of aerobic and sedimentation unit are the main factors affecting the denitrification of the system,on the premise of ensuring denitrification in sedimentation did not seriously affected the separation of sludge from water,proper controlling of aerobic operation and maintenance of denitrification in the sedimentation unit can benifit the denitrification of the system rather than just controlling the anoxic operation.