Study On Structure And Constituent Of Residual Sludge And The Response Mechanisms Of Dewaterability

With the acceleration of urbanization in China,the discharge of domestic sewage is also increasing day by day.As the main by-product of sewage treatment,the output of sewage sludge is also increasing.Sludge dewatering,as an important prerequisite for sludge treatment and disposal,is very important.Sludge composition is complex and there are many factors affecting the dewatering performance.It is of great significance to elaborate the response mechanism between its structural components and dewatering performance for understanding the mechanism of sludge dewatering and improving the efficiency of sludge dewatering.In this paper,the structural components of the sewage sludge were deeply studied.Advanced persulfate oxidation method,polyaluminum chloride and cationic polyacrylamide were used for conditioning.The internal properties of the sludge,changes in the microstructure of the sludge during conditioning,water migration and migration rules were studied.The response mechanism of physicochemical properties and dewatering performance of sludge was discussed,and the main research results were as follows:(1)The moisture content of the sewage sludge was 97%-99%,in which the free water content was 70%-73%and the combined water content was 27%-30%.3D-EEM analysis showed that the fluorescent substances in the sludge were mainly humic acids and microbial metabolites.The content of protein in the gel-like structure was always higher than that of polysaccharide,and the content was higher,which was not conducive to the removal of water in the sludge.The surface structure of the sludge is compact,and the rheological properties of the sludge showed that the hysteresis loop areas of the sludge is 4891 Pa·S-1,and the thixotropy is strong and it is not easy to dehydrate.(2)Activation of sodium persulfate by Fe2+can improve the performance of sludge dewatering.The results showed that when the Na2S2O8 dosage was 18 mmol/L and Fe2+/Na2S2O8 molar ratio was 1:1,the conditioning effect was the best,the water content of sludge cake was reduced to 70.1%,the reduction rates of CST and SRF were 73.0%and 57.4%,respectively.The neutralization of sludge surface charge is the best.The rheological properties of the sludge showed that the hysteresis loop areas and the limiting viscosity of the sludge were decreased after conditioning.The cell cleavage induced by conditioning,which was also beneficial to reducing the abundance of resistance genes in the sludge.(3)PAC conditioning can neutralize the negative charge on the surface of sludge,and the dewatering performance can also be improved.When the PAC dosage was 1.7 g/L,the sludge dewatering effect was the best,and the moisture content,CST and SRF of the sludge cake were all reduced to the minimum values,which were 72.5%,0.53×1012 m/kg and 15.6 s,respectively.The sludge particle size distribution and fractal dimension had no significant changes.The flocs formed by PAC can adsorb and precipitate,which can effectively reduced the contents of protein,polysaccharide in the gel-like structure and total phosphorus of supernatant.After conditioning,the surface of the sludge is dense and the internal pore structure is rich,which is more conducive to the discharge of water in the sludge.(4)CPAM conditioning sludge based on the principles of adsorption bridging,net capture and sweep can effectively increase the particle size of sludge,but the D fractal dimension and the density of sludge decreases.When the dosage of the agent was 0.45 g/L,the sludge dewatering performance was the best,and the moisture content,CST and SRF of the sludge cake were 71.4%,8.4 s and 0.18×1012 m/kg,respectively,which was the biggest improvement degree of sludge filtration performance among the three conditioning methods.The conditioning process had no significant effect on the composition of organic matter and the abundance of resistance genes.(5)Factor analysis was used to explore the relationship between the characteristics of the conditioning process and the sludge dewatering performance.The results showed that two common factors could be extracted,which respectively reflected the characteristics of sludge organic matter and surface charge,and the size of sludge floc.The relationship between water content and each characteristic index can be obtained through principal regression analysis by replacing the original variable with the common factor after rotation.According to the coefficient size of the equation obtained,it can be determined that TPS,SCOD and D50 are the most influential factors on the water content of sludge after conditioning.