Electrokinetic Dewatering of Sewage Sludge with Fixed and Moving Electrodes: Attenuation Mechanism and Improvement Approach

Abstract

This paper presents a laboratory study on electrokinetic dewatering (EKD) of sewage sludge with fixed and moving electrodes. The experiments with fixed electrodes were conducted in two purposely designed Perspex cylinders to investigate the mechanism of attenuation in electroosmotic flow and dewatering efficiency. The experiments with moving electrodes were performed in an innovatively designed apparatus, in which the anode made of an array of stainless rods can be moved toward the fixed cathode plate. The fixed-electrode experiments showed that the electrical resistance of the dewatered section near the anode increased with the treating time, and hence the voltage gradient left for the undewatered section decreased. The increased electrical resistance resulted in an increase in the invalid energy consumption, and the reduced voltage gradient at the undewatered section resulted in an attenuation in electroosmotic flow and dewatering effect. Comparison tests conducted with the moving-anode apparatus further demonstrated the attenuation mechanism. Only a slight attenuation in the electroosmotic flow was observed in the moving-anode experiments, in which the anode array was moved to pass by the dewatered section and keep the voltage gradient on the undewatered section unchanged. As compared with the fixed-electrode experiments, the dewatering effect for the moving-anode experiments was much better, and the energy consumption in terms of removed water volume was significantly lower. When the moving-anode method was applied with a voltage gradient of