Preliminary Study On Synergism And Mechanism Of Biochemical And Physicochemical Phosphorous Removal

Currently, the water eutrophication is becoming increasingly serious. Higher requirements have been placed on the treatment of the main nutrients such as N, P which induced water eutrophication. But, the mutual inhibition between nitrogen and phosphorus removal always exists in the same biological system, and the effluent of biological phosphorus removal process is unstable. Therefore, it is an inevitable trend by using the combination of chemical and biological phosphorus removal.In this paper, in the case of the major operating parameters have been selected (HRT=10h,MLSS=3500 mg/L,SRT=15d,R=100%) of the A / O process which is the traditional biological phosphorus removal technology, the treatment effects by dosing flocculants is studied, whether synergism exist and mechanism of biochemical and physicochemical phosphorous removal are analyzed.In this experiment, three flocculants, which is polymeric aluminum chloride (PAC), polymeric ferric sulfate (PFS) and polymeric aluminum ferric chloride (PAFC), are added at different dosing point (in anaerobic zone, in aerobic zone and in the effluent of secondary sedimentation tank), dosing quantity are 10mg/L, 20 mg/L, 30 mg/L, 40 mg/L, 50 mg/L, 60mg/L, respectively.The optimum dosing quantity of three kinds of flocculants is selected at different dosing points by experiment; Effluent effect is compared between dosing in the biological reactor (in anaerobic zone and in aerobic zone) and dosing in the effluent of secondary sedimentation tank. It is found that when dosing in anaerobic zone, the removal efficiency of TP and COD_cr is better than that dosing in the effluent of secondary sedimentation tank. The removal efficiency of TP ,COD_cr and NH₄⁺-N of dosing in aerobic zone is somewhat increased as compared with dosing in the effluent of secondary sedimentation tank. The results revealed that there was indeed biochemical and physicochemical synergism. The reason and mechanism of synergism is analyzed at the same time. According to dimension, synergism of dosing in aerobic zone is above that dosing in anaerobic zone. Side Effects on the removal efficiency of NH₄⁺-N have been found when dosing in anaerobic zone. It maybe duo to that growth environment of nitrifying bacteria has been influenced by dosing flocculants. Then nitrification is decreased, the removal efficiency of NH₄⁺-N is reduced.In addition,the remoral effects and dimension of synergism of different flocculants are compared with the same dosage in this paper. The results show that the remoral effects and dimension of synergism of PAFC is both better than that of PAC and PFS. So PAFC is the best of three kinds of flocculants, the best dosing point is aerobic condition, the optimum dosing quantity is 40 mg/L. Average removal rate of pollutants is TP:92.32%, COD_cr:87.96%, NH₄⁺-N:82.54% respectively.Influencing factors of biochemical and physicochemical phosphorous removal synergism are analyzed in this paper, such as different dosage of flocculants, whether continuous dosing, pH, temperature etc. The research shows that biochemical and physicochemical phosphorous removal synergism is only embodied in a certain range of flocculants dosage. Chemical and biological flocculation would be affected if flocculants dosage is too high which leads to colloid stability again. Activity of microorganism in the activated sludge system will be affected by excessive flocculent, then the effluent quality is decreased. The ratio of physicochemical sludge in the activated sludge system is continuously increased if continuous dosing. Activity of microorganism will be also affected.