A Comparative Study Of Pretreatment Methods For Excess Sludge Dewatering

Excess activated sludge, usually called as excess sludge or sludge, is a kind ofsemisolid waste produced in the municipal domestic sewage treatment. The treatment anddisposal of excess sludge is rather difficult because of its high moisture content, largeamount of mass and high organic matter content. It is of very important practicalsignificance for the reduction of the wet sludge volume and the mass of the dried solid.The typical sludge pretreatment methods are enzymatic hydrolysis, microwavetreatment, ultrasonic treatment, oxidation and electrical treatment. In this paper, acomparative study is performed to examine the dewatering effect of these pretreatmentmethods, and scanning electron microscope analysis (SEM) is used to investigate theimprovement of the dewatering efficiency.(1) By comparing the sludge pretreatment methods among ultrasonic, microwave,enzymatic hydrolysis and oxidation, it indicates that the best method is oxidation withH2O2, and the optimum parameter is as following: temperature95℃for10minutes,the dosage of H2O2and H2SO4is1.5%and2.5%. Under this condition the moisturecontent in the treated solid is50%-54%and pH value of the filtrate is about1.(2) When the sludge filtrate is reused, H2O2dosage can reduced to about1.2%, just80%of the initial dosage, and H2SO4can reduced to0.5%, only20%of the initial dosageused for the pretreatment.(3) By contrasting the drying rate of the dewatered sludge with and without pretreatmentat different drying temperature, it shows that at60℃,70℃,80℃,90℃, and95℃,the drying time for the dewatered sludge cake with pretreatment is255,230,150,130and95minutes, respectively, but for dewatered sludge cake without pretreatment, the dryingtime change little with the drying time. The result indicates that the dewatered sludgewith pretreatment is easier to be dried than the dewatered sludge without pretreatment insame time.