Chemical-Biological Flocculation Enhanced Primary Treatment In Low Temperature Domestic Wastewater

Many traditional secondary wastewater treatment plants face such problems, namely high construction cost, expensive operating cost, low phosphorous removal, and maladjustment in low temperature case. Chemical-Biological Flocculation Enhanced Primary Treatment (CBEPT) was used in this study to treat low temperature and low concentration domestic wastewater, in which the chemical-biological flocculation was studied emphatically and was compared with the Chemically Enhanced Primary Treatment (CEPT). Meanwhile the flocculation capability of the recycled sludge was analyzed primarily in the Chemical-Biological Flocculation Enhanced Primary Process.The operation parameters of the CBEPT were determined in 12~18℃as follows: ferric sulfate dosage 40mg/L, aeration rate and flocculation time 0.08 m3/h,15min and 0.04 m3/h,25 min, sludge activated aeration time 150 min , sludge concentration 3.2 MLSS/COD.Compared with the condition of 12℃~18℃, the removal rates of COD, SCOD and UV254 were decreased by 20.00%, 33.88% and 16.40% at 5℃~10℃respectively. When ferric sulfate concentration was increased to 60mg/L, the removal rates of COD, SCOD and UV254 were up to 66.67%, 39.71% and 48.39% respectively, which indicated that increasing ferric sulfate dosage could offset the negative influence caused by lower temperature.In 12℃~18℃and 5℃~10℃, compared with CEPT for same influent, CBEPT could not only decrease the dosage of ferric sulfate by 25%~33%, but also improve removal rates of the analysis terms, which of both COD and SCOD were increased obviously, the removal rates of COD were 66.67% and 79.03%, increasing by 12.72% and 23.80% respectively, the removal rates of SCOD were 39.71% and 65.34%, increasing by 24.53% and 49.39% respectively. The removal rates of turbidity and TP were more than 93% and 96% respectively, but that of NH3-N was just 14%, so there was need to treat the effluent by denitrification. The results showed that through recyled sludge CBEPT could decrease ferric sulfate dosage and the removal rates were increased at the same time. Despite ferric sulfate dydrolyzing with OH-, the system kept neutral because the influent was a little alkaline, and microorganism adapted well to the change, so there was no need to adjust pH value. The pH value of the effluent could meet the standard of wastewater discharge.Study on the flocculation capability of the recycled sludge showed that flocculation capability was restrained by chemical dosage, but the sludge still kept efficient adsorption and flocculation, which indicated that this kind of sludge came from a closely chemical-biological-ingrated wastewater treatment process. Extracellular polymeric substances (EPS) concentration was 108.66 mg/gVSS and microorganism was active in the Chemical-Biological Flocculation process.CBEPT has good enhanced removal efficiency to turbidity,COD,TP in low temperature case. It is accordant with the situation of our country: the running and management are convenient, which has important realistic meaning for abating the lack of funds and improving environment and economy development harmony. Therefore CBEPT has a very bright future. This study gave some guidance for the applying and spreading of CBEPT in our country.