Test On Alterable Mode Biochemical Pretreatment For Municipal Wastewater Treatment

This thesis has mainly studied the alterable mode biochemical preceding process in the biology/ecology combination process for pretreating municipal wastewater. There are two modes in the preceding process,which are facultative biochemical mode and biologic enhanced flocculation mode. This paper studied the two modes in 3 trial stages on the foundation of the orthogonal test on the facultative biochemical mode . It is found that the critical temperature of facultative biodegradation in treatment of domestic wastewater is 13℃. Based on the orthogonal test,we have got the most superior condition in treating urban wastewater by the facultative biochemical process.Then experimentations are processed at low temperature(below 13 ℃ )and at normal temperature(from13 ℃ to 24 ℃ ) in the most superior condition. The changes of COD,NH3-N,TN,TP are tested . It is examined that organisms concentration of effluent is between 60-80mg/L which satisfy the influent concentration of subsequernt treatment.But the removal rates of phosphorus and nitrogen are not good.The factors affecting the results are analyzed and the improving methods are brought forward .The organic abstrate(saccharose) is added to the reactor and the the removal rate of contaminations increased from 10%to 20%.It is found that the best dosage of saccharose is the quantity which could keep the COD of influent at about 400mg/L. The biologic enhanced flocculation mode is brought forward for ameliorating the deficiency of facultative biochemical mode at low temperature. We made the beakers experimentation. Firstly,the best flocculent and the best controlling factors coagulation condition at low temperature are found in the flocculation experimentation. The optimum flocculent is PAC.The optimum flocculent dose is 30 mg/L. The optimum agitation intensity is : the high speed n₁=150r/min, medium speed n₂=80r/min and low speed n₃=30r/min ,and the corresponding agitation times are t₁=0.5min,t₂=5min and t₃=15min respectively. Secondly,The flocculent is mixed with facultative sludge and sewage to research the enhanced effect of flocculent and the synergetic effects of flocculent and facultative microbes .It is found that the optimum flocculent dose of PAC is 20 mg/L,the optimum HRT is 8h in the mixture of flocculent and biologic sludge system . The removal rate of COD is 69.50% and it is 15% higher than the simplex sewage flocculation system and the simplex biodegradation system. The removal rate of TP is 50.85% and it is 20% higher than the simplex sewage flocculation system and the simplex biodegradation system.There is no synergetic effects on nitrogen removal.