Influence of Electric Field Application by Reducing Area of Electrode Compared with Cross-Sectional Area of Sludge Bed on Electro-Osmotic Dewatering Process

Abstract

In the process of electro-osmotic dewatering of a semi-solid sludge put between two plate-type electrodes placed above and below a sludge bed, the water content in part of the bed near the upper electrode opposite to a lower drainage surface is considerably reduced, resulting in electrically poor contact between the upper electrode and the bed being dewatered, and then an excessive increase in electrical contact resistance between them. This obviously obstructs the efficiency of electro-osmotic dewatering throughout the entire bed, and consequently, the continuation of the dewatering process becomes increasingly difficult. From the viewpoint of lowering the influence of increasing electrical contact resistance, the usage of an upper plate-type electrode, in which the area of such electrode is smaller than the cross-sectional area of the sludge bed, is regarded to be practical in improving electro-osmotically the performance of sludge dewatering. In this study, electro-osmotic dewatering is experimentally investigated by reducing the area of not only the upper electrode, but both the upper electrode and the lower one on the drainage surface, and compared with the same-area electrode as the cross-section of the bed. Thus, the influence of such electrode arrangements in reducing the area of the electrode(s) on the dewatering process in terms of water removal and electrical energy consumption is examined using calcium carbonate as solid particles for sludge conditioning. As a result, it has been found that the amount of removed water and electrical energy efficiency for water removal can be increased compared with the same-area electrode as the bed, except for the case of an excessively small electrode area.