| Activated sludge process to treat municipal and industrial wastewater produces huge amounts of excess sludges. The treatment of these excess sludge becomes a difficult problem in sewage treatment because of its large volume, complex components and high cost. The water content of it is as high as 95%-99.5%. Therefore dewatering is the key of sludge reduction. The bottleneck of sludge reduction is dewatering because of much of extracellular polymeric substances (EPS). EPS are a complex high-molecular-weight mix coture of excreted by microorganisms, produced by cellysis and hydrolysis, which absorbed organic matter from wastewater. The physical-chemical properties and microbial characteristics of sludge are certainly determined by EPS, which compose 80% of the weight of solid sludge, and the main components of EPS are polysaccharide, protein, nucleic acid, lipid and DNA, etc.Mechanical dewatering is the most common method in sludge reduction. Chemical condition has been adopted widely to improve sludge mechanical dewatering.After using Fenton oxidation to processed excess sludge, in which sludge dewatering capacity was described by the specific resistance to filtration (SRF) and capillary suction time (CST). The effect of pH, reaction time, the dosage of Fe2+ and H2O2 on sludge dewatering capacity was investigated. The objective of this study was to optimize the operational conditions for sludge dewatering capacity with Fenton oxidation. Based on the best condition, the effects of various pH on SRF, CST and static balance time (SV30) were investigated. The results showed that the sludge dewatering capacity improvement by Fenton reaction was higher than that by acid treatment. The optimal operational conditions for the experimental sludge were: pH=2.5, reaction time=60 min, H2O2 dosage=6 g/L and Fe2+ dosage=4 g/L. Under these conditions, SRF and CST reduced from 34×1010s2/g and 69.6s to 1.31×109s2/g and 20.6s, dewatering capacity was improved obviously. After Fenton reaction, raising pH can improve dewatering capacity but affects settlement of sludge seldom.Photo-Fenton reaction was used to oxidize excess sludge, in which sludge EPS disintegration was characterized by the concentration of soluble chemical oxygen demand (SCOD), polysaccharide and protein of sludge supernate, and sludge dewatering capacity was described by the SRF and the water content of the sludge cake. The results showed that the effect of EPS disintegration and sludge dewatering capacity improvement by photo-Fenton reaction was higher than that by Fenton reaction or UV radiation. The optimal operational conditions for the experimental sludge were:pH=3, reaction time=2 h, H2O2 dosage=4 g/L and Fe2+ dosage=0.6 mg/L. Under these conditions, the concentration of SCOD, polysaccharide and protein of the sludge supernate increased from 67.46 mg/L,12.53 mg/L and 8.62 mg/L to 568.12 mg/L,448.62 mg/L and 292.94 mg/L, respectively; and the SRF and the water content of filter cake reduced from 2.4x109 s2/g and 88.52% to 5.26x108 s2/g and 76.36%, respectively. The efficient EPS disintegration and dewatering capacity improvement of the excess sludge was simultaneously achieved by photo-Fenton, which benefits the further sludge reduction.
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