Research On Dewatering Performance Of Sludge After Fenton Oxidation And Anaerobic Digestion

Sludge with high moisture content needed to be dewatered to reduce the sludge volume for facilitating transportation and subsequent disposal. The parameters for the condition of excess sludge by Fenton reagent were investigated, and the capillary suction time (CST), the specific resistance to filtration (SRF) and the water content of sludge cake were measured to examine sludge dewatering performance. The effects of initial pH of sludge, H2O2 dosage, H2O2/Fe2+ ratio, reaction time and temperature on sludge conditioning were investigated. The optimal condition parameters for sludge conditioning were determined as follows:pH=3, H2O2 dosages of filtration and centrifugal dehydration were 3g/L and 9g/L respectively, H2O2/Fe2+ ratio (mass ratio)=8-12, temperature T=50℃, and reaction time was 60min. The protein and polysaccharide contents in extracellular polymeric substances (EPS) increased after the excess sludge was conditioned by Fenton reagent, which demonstrated that Fenton oxidation could effectively break EPS structure and improve the flocculation and dewatering performance of sludge. After Fenton oxidation, sludge particle size became smaller and the surface area increased.The change of dewatering performance of digested sludge was studied as well here. The result showed that SRF value of digested sludge was a little smaller than that of raw excess sludge, the filtration rate of digested sludge increased a little. PAM, FeCl3, and PAC were used in the sludge conditioning experiment, which revealed that the optimal dosages of digested sludge all increased compared to excess sludge and dewatering performance of digested sludge became worse. Through analyzing extracellular polymeric substances (EPS) content and the characteristics of sludge particle, it was found that digestion process led to the degradation of EPS and releasing into liquid. With the decreasing of EPS content in sludge, the larger floc formed by the bridging of EPS was disintegrated into smaller particles. The proportion of smaller particles in sludge increased and dewatering performance of digested sludge became worse.Pilot scale experiment of sludge deeply dewatering with frame filter press had carried out, the result showed that the combination of Fenton reagent and ferric salt and the combination of ferric salt and lime had a good conditioning performance, the water content of sludge cake was below 60%. Compared with ferric and lime, the combination with Fenton reagent and ferric salt showed higher performance on sludge conditioning, such as more stability of sludge, less amount of sludge, higher caloric value and closer to neutral pH value of sludge cake even though it cost more time for sludge to get to the filter press.