Chemically-Activated Sludge Adsorption And Flocculation In Domestic Sewage Treatment

Chemically-activated sludge flocculation and adsorption on domestic sewage treatment is a new wastewater treatment. Chemical flocculation (CEPT) is particularly suitable for rapidly growing cities, it is bad for soluble organic (SCOD) removal, but good for non-soluble organic (NSCOD) removal and phosphorous removal, meanwhile, SCOD is flocculated and adsorbed by excessive activated sludge efficiently, thus combining CEPT with activated sludge flocculation can utilize their advantages to promote contaminants removal rates,and save disposal fee of excessive activated sludge.The best mechanical mixing condition of activated sludge adsorption and flocculation is 400rpm rapid mixing 30minutes, 80rpm flocculation 15minutes, sedimentation 15minutes, activated aeration time 3 hours, MLSS/COD 5~10; the best aeration condition is aeration flow 0.05~0.10m3/h, aeration time 40min~1h, sedimentation 15minutes, no activated aeration time, MLSS/COD 3~5; comparing two mixing modes shows aeration mixing is better.The best aeration mixing condition of CEPT is mixing flow 0.15 m3/h, mixing time 30 seconds, flocculation flow 0.025 m3/h, flocculation time 5 minutes, sedimentation 15minutes, when dosing 60mg/L ferric sulfate , the removal rates of turbidity,COD,SCOD and TP are 82%,54%,8% and 90% respectively. As the same ferric sulfate dosage , the removal rates of turbidity,COD,SCOD and TP by mechanical mixing are almost higher than those by aeration mixing, thus the mechanical mixing is better.Comparing two dosing modes of chemically-activated sludge flocculation , as the same ferric sulfate dosage and activated sludge dosage, the removal rates of turbidity,COD,SCOD,UV254,TP and PO4-P by adding ferric sulfate then activated sludge are higher than those by adding activated sludge then ferric sulfate. The best dosing mode is adding ferric sulfate by 400rpm rapid mixing for 10 seconds then adding activated sludge by 40 minutes aeration , sedimentation 20 minutes. Adding 60mg/L ferric sulfate and 2.5 MLSS/COD activated sludge , the removal rates of turbidity,COD,SCOD,NSCOD,UV254,TP and PO4-P are 87%,80%,70%,89%, 44%,90% and 100% respectively。The recycling chemically-activated sludge don't need activated aeration, the more the recycling chemically-activated sludge adds , the higer the removal rates of turbidity,COD,UV254,TP and PO4-P are , the removal rates increase with the dosage of ferric sulfate increasing, when adding 60mg/L ferric sulfate, the removal rates of turbidity,COD,SCOD,UV254,TPand PO4-P are 88%,78%,65%,43%,88% and 100% respectively.The removal rates of turbidity,COD,SCOD,UV254,TP and PO4-P by the recycling chemically-activated sludge and ferric sulfate flocculation is a little lower than that by fresh activated sludge and ferric sulfate flocculation, but recycling chemically-activated sludge realizes reuse of sludge and reduces excess sludge.Chemically-activated sludge flocculation and adsorption treatment exhibited higher removal rates than those using activated sludge or CEPT only.