Disposal of Alum Sludge to the Existing Activated Sludge Wastewater Treatment Plant

Abstract For finding the practicability of discharging water treatment plant sludge into the municipal sewer, the effects of synthetic aluminum hydroxide floc on several major units in an activated sludge wastewater treatment process were studied. It was found that the crucial effects were the increase in sludge production, either in the primary settling tank or in the secondary settling tank, and the retardation of the digestibility of the wasted sludge. The treatment efficiency, in terms of the quality of the treated wastewater, however, was improved. No toxic effects were found in the study of the functions of organic matter removal and the nitrification of activated sludge with the addition of aluminium hydroxide up to 300 mg Al/1 to the mixed liquor. The dewatering property of the wastewater sludge was improved with the addition of this chemical floc. Two processes are suggested. One is to discharge alum. sludge into the sewer at a suitable rate and the other is to discharge the water treatment wastes into a thickener in the wastewater treatment plant. The concentrated underflow can be mixed with the regular digested sludge for dewatering while the supernatant can be discharged either to the primary settling tank or to the aeration tank.