Removal of Waterborne Particles by Electrofiltration: Pilot-Scale Testing

Abstract

Theoretical analysis using a trajectory approach indicated that in the presence of an external electric field, charged waterborne particles are subject to an additional migration velocity that increases their deposition on the surface of collectors (e.g., sand filter). Although researchers conducted bench-scale experiments to verify the effectiveness of electrofiltration, few studies have reported on the applications of electrofiltration in larger scale facilities. In this study, a prototype pilot-scale electrofiltration unit, consisting of an acrylic tank (0.3 × 0.3 × 1.2 m) with vertically placed stainless steel mesh electrodes embedded in a sand filter was tested at a local drinking water plant. Presedimentation basin water was used as the influent with a turbidity ranging from 12 to 37 NTU. At an approach velocity of 0.84 mm/s, an electrode voltage at 8 and 12 V increased the particle removal coefficient pC* [defined as −log(Cout/Cin)] to 1.79 and 1.86, respectively, compared to 1.48 when there was no electric field. Reducing the approach velocity from 0.84 to 0.42 mm/s increased pC* from 1.48 to 1.64, when the electrode velocity was 16 V. Repetitive experiments were conducted and the results were in agreement with those calculated by a theoretical trajectory analysis. The electrofiltration process was demonstrated to be more effective for removal of smaller particles (<4 μm), the size range of many waterborne bacteria. A voltage of 8–12 V was shown to be the most cost-effective range, considering both the energy cost and filtration performance. The findings from this pilot-scale study are important for full-scale applications of the electrofiltration technology.