Effect Of Flocculation Conditioning On Dewatering And Flow Performance Of Municipal Sludge

With the acceleration of urbanization in China,the discharge of sewage sludge increased.Usually,sludge contains a large amount of moisture,inorganic particles,organic residues,pathogenic microorganisms,harmful heavy metals and other refractory substances.The moisture content is about 96%~99% of sludge mass.It is difficult to dehydrate because of complex components.Due to the flow state of sludge in the whole sewage treatment system,it is necessary to study flow performance of sludge.In this paper,the regurgitant sludge of a sewage treatment plant was used as object of research.The inorganic flocculant PAC and the organic flocculant CPAM were used to pretreat the sludge.Effects of flocculation pretreatment on sludge dewatering performance under different dewatering methods were studied by sedimentation,centrifugation,batch filtration and continuous filtration dewatering experiments.At the same time,the influence of flocculant on the rheological property of sludge was investigated,and the relationship between dewatering property and rheological property of sludge was analyzed.Main conclusions are as follows.(1)Flocculation conditioning could effectively improve the physical and chemical properties of municipal sludge.CPAM could increase the sludge particle size and increase the p H value.PAC could slightly increase the sludge particle size and decrease the p H value,while the combination of two flocculants can improve p H stability and increase particle size of sludge.(2)In order to improve dewatering performance of sludge,filtration rate,filtration specific resistance and filtrate turbidity were proposed as indexes to measure the sludge filtration performance.Solid content of sludge cake,bound water content and sludge volume reduction rate were proposed as indexes to measure the sludge dewatering performance.Results showed that PAC can effectively improve settling and dewatering performance of sludge,while CPAM had no obvious effect on sludge settling performance.The effect of composite agent on the sludge settling performance was stronger than that of flocculant alone.PAC,CPAM and compound agents had little effect on centrifugation performance of sludge.The addition of flocculant can significantly improve filtration performance and dehydration performance of sludge.When the amount of PAC reached 80mg/g,solid content of filter cake and filtration rate reached optimum;when the addition amount of CPAM reaches 5mg/g,the solid content and filtration rate of cake reached the optimal;the addition of composite agent could improve filtration performance of sludge,the filtration rate increased obviously,but the effect on sludge dewatering performance was limited.(3)Sludge is a kind of non-Newtonian fluid with yield value and pseudoplasticity.Flocculation conditioning can improve solid characteristics and thixotropy of sludge.The optimal dosage of flocculant can be calculated by rheological parameters.Viscosity had an effect on solid content of the dehydrated sludge,and the filtration resistance of sludge cake was correlated with the composite modulus and the composite compliance.