Magnetic field enhanced cake filtration of superparamagnetic PVAc-particles

Enhanced technology based for sewage sludge deep dewatering: A critical review

Sludge is an inevitable by product of sewage treatment, and it includes pathogens, heavy metals, organic pollutants and other toxic substances. The components of sludge are complex and variable with extracellular polymeric substances (EPS) being one. EPS are highly hydrophilic and compressible, and make sludge dewatering difficult. Therefore, the development of efficient sludge-dewatering technology is an important means of mitigating rapid sludge growth. At present, the main methods used for sludge deep-dewatering technology are chemical preconditioning with high-pressure filtration and electrical mechanical dewatering. The selection of chemical preconditioning directly determines the final efficiency of the sludge-dewatering process. In this paper, we conduct a comprehensive review of the problems related to sludge dewatering and systematically summarise the impact of different chemical conditioning technologies on the efficiency of sludge dewatering. Furthermore, the characteristics of different enhanced dewatering technologies are evaluated and analysed for their adaptability and final disposal methods. We believe that this review can clarify the chemical conditioner mechanism to improve sludge dewatering, provide reference debugging information for the sludge-dewatering process and promote the development of efficient and environmentally friendly sludge-dewatering technology.

Study on the effect and mechanism of hydrothermal pretreatment of dewatered sewage sludge cake for dewaterability

In China, over 17 million tons dewatered sewage sludge cake (DSSC), with about 80% water content, was generated from wastewater treatment plants in 2010. High water content is the bottleneck of sludge treatment and disposal. In this study, the combination of hydrothermal and mechanical treatments has been chosen in order to improve sludge dewaterability. Sludge thermogravimetry analysis was conducted to determine 180 degrees C as the upper-limit hydrothermal temperature. Five temperatures (60, 80, 120, 150, 180 degrees C) were chosen to study the effects of hydrothermal treatment temperature and the holding time on dewaterability. The higher the hydrothermal temperature, the better was the dewaterability character. The water contents of solid products were positively correlated with the hydrothermal holding time at predetermined temperatures in this study. Degradation of macromolecules into acidic compounds could be the reason of pH decrease of separated liquid. Destruction of zoogloe and decomposition of organic matters improved the sludge dewaterability. Sludge dewaterability experiencing hydrothermal processes in this study was negatively correlated with extracellular polymeric substance (EPS) content. With the rising temperature, sludge flocculate disaggregated to small particles generally, this could also be one of the important reasons for sludge dewaterability.

IMPLICATIONS

High water content is the bottleneck of sludge treatment and disposal. Up to now, only a small amount of research has been conducted to determine whether the dewaterability of dewatered sewage sludge cake can be improved by hydrothermal pretreatment. The mechanism of sludge dewaterability by hydrothermal pretreatment is uncertain. In this study, a new sludge disposal method and corresponding parameters were given. The mechanism of sludge dewaterability was analyzed extensively by extracellular polymeric substances, scanning electron microscope images, element contents, and caloric values, etc. This study will be helpful for knowing about sludge hydrothermal pretreatment technology and its mechanism.

Electrical field: a historical review of its application and contributions in wastewater sludge dewatering

Electric field-assisted dewatering, also called electro-dewatering, is a technology in which a conventional dewatering mechanism such a pressure dewatering is combined with electrokinetic effects to realize an improved liquid/solids separation, to increase the final dry solids content and to accelerate the dewatering process with low energy consumption compared to thermal drying. Electro-dewatering is not a new idea, but the practical industrial applications have been limited to niche areas in soil mechanics, civil engineering, and the ceramics industry. Recently, it has received great attention, specially, in the fields of fine-particle sludge, gelatinous sludge, sewage sludge, pharmaceutical industries, food waste and bull kelp, which could not be successfully dewatered with conventional mechanical methods. This review focuses on the scientific and practical aspects of the application of an electrical field in laboratory/industrial dewatering, and discusses this in relation to conventional dewatering techniques. A comprehensive bibliography of research in the electro-dewatering of wastewater sludges is included. As the fine-particle suspensions possess a surface charge, usually negative, they are surrounded by a layer with a higher density of positive charges, the electric double layer. When an electric field is applied, the usually negative charged particles move towards the electrode of the opposite charge. The water, commonly with cations, is driven towards the negative electrode. Electro-dewatering thus involves the well-known phenomena of electrophoresis, electro-osmosis, and electromigration. Following a detailed outline of the role of the electric double layer and electrokinetic phenomena, an analysis of the components of applied voltage and their significance is presented from an electrochemical viewpoint. The aim of this elementary analysis is to provide a fundamental understanding of the different process variables and configurations in order to identify potential improvements. Also discussed herein is the investigation of the electrical behaviour of a porous medium, with particular emphasis on porous medium conductivity determination.