Modification of slow sand filtration of secondary effluents by electric fields: electrokinetics and influence factors

In this study, the effect of electric fields applied to a quartz sand bed on electrokinetics and the disinfection performance of an E-slow sand filter (reduction of Escherichia coli) were investigated. Results of electrokinetic experiments have shown that coliforms are electroosmotically transported to the cathode with a velocity of 0.6 cm h(-1) (E = 4 V cm(-1)). In the absence of an electric field and at electric field strengths of <4 V cm(-1), a diffuse random movement to the cathode and the anode was the only translocation mechanism. Hence, the electroosmotic transport may represent an additional component of motion during E-slow sand filtration influencing its disinfection performance. Based on this, comparative experimental investigations on the disinfection performance of a slow sand filter without and combined with an electric field were carried out. In the absence of an electric field, the adsorptive filter effect of quartz sand contributes to an initial bacterial retention by 0.8 log levels. Applying an electric field strength of 4 V cm(-1) caused an increase of E. coli reduction up to 4 log levels. The electrokinetically enhanced accumulation of E. coli in the filter bed is assumed to be the major effect mechanism in the E-slow sand filter.