Effect Of Compound Thermal Hydrolysis On Sludge Characteristics And Dehydration

With the rapid development of urbanization,the amount of sludge which produced with wastewater increased significantly.However,there is a lack of efficient and economical sludge treatment and disposal method.The sludge is difficult to dewater without pretreatment,due to its complexity composition.The current sludge pretreatment methods mainly include chemical flocculation,sonication and thermal hydrolysis.Thermal hydrolysis is better for improving sludge dewatering performance,and it is beneficial to reduce total solid phase of sludge,but it has high energy consumption,which is not conducive to industrial applications.The purpose of this article is to reduce energy consumption of thermal hydrolysis.The return sludge from secondary sedimentation tank of a sewage treatment plant in Taiyuan,Shanxi was used as the research object,and thermal hydrolysis combined with chemical reagents were introduced.The effects of different process conditions including thermal hydrolysis temperature?thermal hydrolysis reaction time 1.5h?and concentration of chemical reagents on sludge characteristics and dehydration were studied,then the optimal condition for thermal hydrolysis combined with chemical reagent pretreatment was determined.The main conclusions were as follows.?1?Studies on physical properties of thermally hydrolyzed sludge alone showed that thermal hydrolysis had a destructive effect on sludge,and macromolecular substances could be decomposed into soluble or small molecular substances.The organic content,the particle size and the p H of sludge all decreased after thermal hydrolysis alone.Based on the mechanism of thermal hydrolysis with Ca?OH?₂determined that the optimal addition concentration of Ca?OH?₂was 150mg/g DS?dry solid mass in sludge?.It was clarified that alkali can not only inactivate cells and dissolve proteins and lipids to destroy cell membranes,but also inhibit the ability of microbial cells to resist high temperature to promote thermal hydrolysis.In addition,it was also pointed out that the optimal concentration of Ca Cl₂was 35mg/g DS.The particle size of sludge treated by compound thermally hydrolyzed?with Ca Cl₂?was lower than that of thermal hydrolysis alone,indicating that Ca Cl₂could promote floc cracking.?2?Based on the centrifugation and filtration dehydration theory,the optimal dehydration method for thermally hydrolyzed sludge alone was determined.The centrifugal dehydration of treated sludge was better at60?-150?,and the vacuum suction filtration was better of that at 175?-200?.The dehydration experiment showed that the upper limit temperature is 150?by thermal hydrolysis with Ca?OH?₂?optimum concentration:150mg/g DS,thermal hydrolysis time:1.5h?.It was a key factor to improve the dehydration performance of thermally hydrolyzed sludge below 150?.It was revealed that Ca?OH?₂was beneficial to the floc decomposition for improving sludge dewaterability,and promote sludge re-flocculation and increase the inorganic content of sludge.The thermal hydrolysis with Ca Cl₂?optimum concentration:35mg/g DS,thermal hydrolysis time:1.5h?changed the protein and polysaccharide in the sludge,and then enhanced the sludge dewaterability by changing the internal interaction and microstructure of the floc.The upper limit temperature of thermal hydrolysis with Ca Cl₂is 135?,and Ca Cl₂can improve the dehydration of thermally hydrolyzed sludge below 135?.The best process route for deep dewatering of low-concentration sludge was determined,which was as follows:the thermal hydrolysis temperature:90?,the holding time:1.5h,the concentration of Ca Cl₂:35mg/g DS,and the dewatering methods:vacuum filtration.