The Improved Process Of A~2O Process

With water eutrophication issue becoming increasingly prominent and the effluent standards improving constantly,nitrogen and phosphorus removal has become one of the focuses of wastewater treatment research.As basic biological nitrogen and phosphorus removal process,many problems exist in the traditional A2O process that can remove phosphorus and nitrogen simultaneously by biological method,for instance:firstly,PAO and denitrifying bacteria rival for limited carbon source,which results in that high removal for phosphorus and nitrogen simultaneously hardly is realized in the process;Secondly,to obtain a high removal effect for nitrogen,it needs a high internal return sludge ratio,which leads to high operation cost. As for the above mentioned,in 1997,gao ting yao and zhang bo of tong ji university bring forward to a new distribution way of carbon source about A2O process,that is reversed A2O process in which anoxic tank is the first tank and anaerobic tank is the second one.But this process also has the contradiction of carbon source,so multi-influent and inversed A2O process is put forward.A large number of documents indicates that inversed A2O process has better removal efficiency of COD,TN,TP,and its outlet concentration changes largely with the inlet concentration.Directing at our province situation,the research is to study and develop a new process of municipal sewage biological phosphorus and nitrogen removal,and to supply reference for current sewage plants renovating or for sewage plants.This research adopted commutative multi-influent and inversed A2O process to treat the effluent of the primary sedimentation tank(in which, COD was 100mg/L～200mg/L,NH3-N was about 50mg/L,PO43--P was 1 mg/L～3mg/L )in tai yuan sewage plant so as to study the selection of parameters and the factors that influenced the effectiveness of municipal wastewater treatment.Referring to the literature results,the initial operational parameters of this experiment were listed as followed : Sludge concentration was between 2500mg/L and 4000mg/L;Aerobic zone DO=2~3mg/L;Sludge return ratio R=200%;Water temperature was 18℃;Total HRT was about 16~20h.The -test consists of 7 parts as followed:1.Under the operational parameters above-mentioned,the author of this article did six tests.After the treatment,the average removal rate of NH3-N is 58.4%, PO43--P is 39.7%,and COD is 71%.In the outlet water,NH3-N is only lower than 20 mg/L,which can only meet the requirement of the second class emission standard,PO43--P can reach the first class B emission standard,although its removal rate is relatively lower,COD is about 50 mg/L,which can only reach the first class B emission standard.So, the experiment analied the reasons form the factors affecting the removing of the nitrogen and phosphorus.2.When the temperature of the system is changed to 25℃, 30℃and 35℃from 18℃, the results showed that: the removal rate of NH3-N is 98.2% and reach the maximum under 30℃,PO43--P is 67.5% and reach the maximum under 25℃.In the outlet water, NH3-N is lower than 2 mg/L and PO43--P is 1.0mg/L which can reach the first class A emission standard. But COD seems to be no significant changes when temperature varied.SO 25℃of the water is advised.3.When the proportion of the anoxic zone and the anaerobic zone is reduced from 3:1 to 2:1 and 1:1, the results showed that: the removal rate of PO43--P decreased from 85% to 40.5%,COD and NH3-N seems to be no significant changes.So,it is advised that the proportion of the anoxic zone and the anaerobic zone is 3:1.4.When DO of the aerobic zone is changed from 2~3mg/L to 1mg/L and 4mg/L, the results showed that: the removal rate of NH3-N and COD increased with DO growing,but PO43--P decreased. So, it is advised that DO is between 2mg/L and 3mg/L.5. When sludge return ratio is changed from 200% to 150% and 250%, the results showed that: the removal rate of PO43--P increased with sludge return ration growing, but NH3-N and COD seems to be no significant changes. So, it is advised that sludge return ratio is 250%.6. When C/N is changed from 4 to 7.5 and 10 after adding the glucose to the water, NH3-N and COD in the outlet water is larger,but PO43--P is a little smaller.So, it is advised that C/N is is 4.7. When the system is running at optimal parameters (aerobic zone DO = 2 ~ 3mg / L; sludge return ratio R = 250%; water temperature 25℃; the ratio of the anoxic and anaerobic zone is 3:1; Total HRT: 16 ~ 20h), NH3-N and PO43--P in the outlet water can reach the first class A emission standard, but sometimes COD is more than 50 mg/L.Therefore, the experiment has been on the study about the further treatment of the outlet water of the system with the compounds of diatomite and coagulants,so that the final outlet COD is much less than 50 mg/L.