Studies On Enhancement And Mechanism Of Waste Activated Sludge Filteration Dewatering Performance With Combined Process Of Pre-lysis And Re-flocculation

Due to the improvement and popularization of municipal wastewater treatment, sludge production had a dramatic increase in recent decades. It will pose a significant threat to the ecology system if it is not properly disposed. Waste activated sludge from secondary settling tank generally contains over 99% water. Sludge with high moisture content may result in the issues of great bulk, expensive cost and difficult for transportation. Development of highperformance dewatering process is the important way to relieve the pressure of rapid increase in waste activated sludge production and also is a hot issue in the field of environmental engineering in China. Currently, the mainstream technology for activated sludge deep dewatering is high-pressure compression filtration process and the dewatering performance was mainly dependent on selection of sludge devices and chemical conditioning methods except for sludge properties.Extracellular polymeric substances（EPS） may lead to the deterioration of sludge dewatering performance due to its high hydrophilicity in waste activated sludge system. Hence, two conditioning methods（enzyme and calcium peroxide treatment） were used to improve the sludge filteration dewaterability by using EPS components dissolution which may lead to the release of sludge bound water and chemical re-flocculation which can reconstruct sludge floc structure. Firstly, reaction parameters and process of sludge combined conditioning were improved and EPS distribution, composition and morphological properties were analyzed. In addition, sludge hydrolysis kinetics models were developed to unravel the sludge conditioning mechanism. The investigate may provide theoretical instruction for application of sludge treatment with enzyme and calcium peroxide to promote sludge dewatering pre-treatment upgrading. Main contents and results of this dissertation are as follows:The feasibility of combined process of composite enzymatic treatment and chemical flocculation with inorganic salt coagulants was investigated in this study. It suggested that sludge filtration performance was deteriorated due to release of a large amount of biopolymers after enzymatic treatment. α-amylase exhibited better performance than protease in sludge solubilization. Moreover, EPS was more extractable after enzymatic treatment, producing looser floc structure. The change in EPS followed the first-order kinetic equation well under enzymatic treatment. The feeding modes of enzymes had a significant influence on sludge lysis efficiency under compound enzymes treatment. α-amylase + protease was more effective in solubilization than other two addition modes（protease + α-amylase or simultaneous addition）. Both of filtration rate and cake solid content were improved with increasing dosage of inorganic salt coagulants and the cake moisture content decreased 15.5% compared with the raw sludge.This study investigated the effects of waste activated sludge filteration dewatering performance with combined process of moderate calcium peroxide pre-oxidation and chemical re-flocculation. It suggested that waste activated sludge dewaterability was relatively enhanced by using moderate CaO₂ pre-oxidation and the optimum dosage was 20 mg/gTSS. Sludge floc was effectively broken and its structure became much looser after CaO₂ addition. Meanwhile, tightly bound EPS（TB-EPS） component gradually converted into loosely bound EPS（LB-EPS） and soluble EPS（SEPS）. The variation in SEPS component can be fitted well with pseudo-zero-order kinetic model. The reaction rate of SEPS was 0.0148 mg/（L?min）. Sludge floc structure was reconstructed and sludge dewaterability was significantly enhanced after chemical re-flocculation by using coagulants of PACl, FeCl₃ and PAM. The sludge cake moisture content could be decreased to 80% below with inorganic coagulants of PACl and FeCl₃ due to their high charge density.