Effect Of Permeability And Stress State On Dehydration Of Sludge In Its Pressurization Process

The mechanical dehydration method is generally used for reducing the moisture content in sludge.However,there is little understanding on the physical and mechanical properties and dehydration mechanism of sludge during pressurization.In order to have a deeper understanding of sludge and its process of pressurized dewatering,and a more solid theoretical foundation for sludge dewatering,characteristics of sludge were studied from the perspective on soil mechanics in this paper.The water permeability,loading conditions,and dehydration performance of the sludge during the pressurization process were analyzed through a series of geotechnical laboratory experiments,such as liquid-plastic limit combined test method,falling head permeability test,compression test,and so on.The results showed that the pore structure,compressibility coefficient,consolidation coefficient,and permeability coefficient of the sludge are related to the dehydration rate.The conditioners that mixed with sludge could increase the dewatering rate through reducing the sludge viscosity,changing the water status,and increasing the permeability coefficient.The two conditioners used in this study increased the dehydration rate of the sludge from 27.5% to 52.6% and 63.9%,respectively.The consolidation and drainage process of sludge follows the principle of effective stress,which is a process in which the excess pore water pressure gradually dissipates and the effective stress increases.Unlike the seepage consolidation of ordinary clay which has only one stage,the removed water in seepage consolidation of sludge include bound water in addition to free water,and it could be divided into three stages.The water content at the end of each stage corresponds to the liquid limit,plastic limit,and shrinkage limit of the sludge.Our study provides a novel insight for understanding the deep dewatering of sludge,analyzes the physical and mechanical properties that affect the dehydration rate,describes stress state in the process of sludge pressure dehydration,explains the conditioning effect of conditioners from the perspective of the change of soil mechanics indexes,and is beneficial to essentially solve the problem of sludge dewatering.