Coupling electro-dewatering and low-temperature air-drying for efficient dewatering of sludge

Abstract

Abstract This study investigated the effects of electro-dewatering on subsequent low-temperature drying at various potentials and the characteristics of low-temperature air-drying sludge were explored through experiments and multi-physical modeling. Experimental results showed that the extracellular polymeric substance (EPS) content in the sludge was reduced during electro-dewatering process, even the species of organic matter was changed, as well as the dewatered cake tend to form many seepage channels, crack and a certain number of holes. These changes in the properties and structure were conducive to the subsequent low-temperature drying process. For air-drying process, the mass of the sludge cake variation was simulated and results were consistent with the experimental phenomenon. Firstly, the weight of the sludge cake was decreased approximately linearly with time, then tended to stable and reached the dewatering limitation finally. The applied higher electric field intensity (25 V cm−1) in the front-end electro-dewatering were conducive to promote water vapor diffusion activity in air-drying stage. Energy consumption and yield analysis results indicated that the combined technology has lower energy consumption and higher yield than that of directly low-temperature drying.