Study On The Deeply Dewatering Of Sewage Sludge By Oxidative Disruption And High-pressure Filtration

The operation of municipal sewage treatment plant could generate a large amount of sewage sludge. It is difficult to reduce the high water content of sewage sludge, causing a lot of environmental problem. The main method of sewage sludge treatment is conditioning with organic polymers before mechanical dewatering, which can only achieve the sludge water content of 80%. Previous studies have indicated that the high affinity for water of extracellular polymeric substances (EPS) confines the dewaterability of sludge significantly. In this paper, the oxidation reaction was used to disrupt EPS and release the bound water. Additionally, a high-pressure filtration technology was firstly applied, in order to enhance the depth of the sludge dewatering.Four oxidants (KMnO4, NaClO2, Ca(C10)2 and Fenton’s reagent) combined with ferric chloride and lime were investigated for sludge dewatering. The changes of the dewatering performance index such as specific resistance to filtration (SRF), capillary suction time (CST), total organic carbon (TOC), protein, polysaccharide and DNA concentration in the sludge supernatant were studied. The results indicated that the oxidants could collapse EPS obviously, leading to the increase of the TOC, polysaccharide and DNA concentration. However, the SRF decreased gradually only when the dosage of KMnO4 increased. Under the KMnO4 dosage of 10 mg/g, FeCl3 dosage of 40 mg/g and CaO dosage of 100 mg/g, the SRF reduction efficiency could achieve 90.7%, and the water content of sludge cake could be reduced to 62.1% by high-pressure filtration. The reaction products of KMnO4 oxidation, which have the flocculation effect, could re-flocculate the sludge fragments, resulting in the improvement of sludge dewaterability. Furthermore, the preliminary investigation of the use of Fenton reagent combined with CaO achieved the better dewatering performance, which the SRF reduction efficiency of 94.8% and the sludge water content of 58.4%.Due to the drawbacks of the present Fenton treatment technology, this study also aimed to develop a rapid and practical Fenton treatment technology for sludge dewatering based on the above experimental results. The results indicated that the Fenton reaction time could be shortened to 5 min while sludge dewaterability was improved significantly. An orthogonal experimental design method was used to optimize the rapid Fenton treatment process. Under the conditions comprising pH 3, Fe2+ of 50 mg/g DS, H2O2 of 30 mg/g DS and lime of 50 mg/g DS, at which the SRF reduction efficiency of 96.4% was achieved. The dosage of Fe2+ was demonstrated to be the most significant factor affecting sludge dewaterability. Furthermore, the lowest EPS concentration in the sludge supernatant was measured under the optimal conditions. And the changes of the particle size of treated sludge samples showed a process of disintegration and re-flocculation of the sludge flocs. These results suggested that the Fenton’s reagent acted both as an oxidant and as an effective coagulant for the sludge fragments. The morphology of the sludge cake exhibited a relatively regular and spongy block-like structure, which could maintain high permeability during high-pressure filtration. With high-pressure filtration technology, the water content of sludge cake could be reduced to 55.1%. Consequently, the rapid Fenton treatment combined with high-pressure filtration can be a promising technique for sewage sludge dewatering.