Effect of permeability and loading conditions on dehydration of sludge in its pressurization process
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ORIGINAL PAPER
Effect of permeability and loading conditions on dehydration of sludge in its pressurization process Z. Xiaochun1,2 · F. Yao1,2 · H. Ying1,2 Received: 1 March 2020 / Revised: 17 September 2020 / Accepted: 28 September 2020 © Islamic Azad University (IAU) 2020
Abstract The mechanical dehydration method is generally used for reducing the moisture content in sludge. However, there is little understanding of the physical and mechanical properties and dehydration mechanism of sludge during pressurization. In this paper, characteristics of sludge were studied from the perspective of soil mechanics. The water permeability, loading conditions, and dehydration performance of the sludge during the pressurization process were analyzed through a series of geotechnical laboratory experiments. 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 by 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. Unlike the seepage consolidation of ordinary clay, which has only one stage, the seepage consolidation of sludge could be divided into three stages. The removed water in the first stage is mainly free water; the discharge in the second stage is the combination of free water and bound water, and bound water was mainly discharged in the third stage. 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 and is benefit to solve the problem of sludge dewatering. Keywords Sludge · Pressurized dehydration · Conditioner · Permeability coefficient · Compression and consolidation
Introduction Sludge is a solid waste from the sewage treatment process and generally discharged from the secondary settling tank or sedimentation clarifier. It is generally contains more than 98% water than mass (Elliot and Mahmood 2007). The sludge composition is complex, including nitrogen, phosphorus, organic matter, trace elements, and even toxic and hazardous substances which are concentrated and difficult to Editorial responsibility: Binbin Huang. * H. Ying [email protected] 1
School of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004, People’s Republic of China
Hebei Province Key Laboratory of Deep Remediation of Heavy Metals in Water and Resource Utilization, Yanshan University, Qinhuangdao 066004, People’s Republic of China
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be degraded, such as heavy metals and pathogenic bacteria. Long-term accumulation of excess sludge will contaminate water bodies and soil, and even threaten ecological safety and human health (Ras et al. 2008). According to the Global Environmental Pr
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