Electroosmotically enhanced sludge pressure filtration

Wastewater sludge is routinely dewatered to lower the cost of transportation and disposal. Dewatering is achieved via vacuum filtration, centrifugation, sand beds, and belt filter presses. Electroosmosis, the movement of water in the influence of a direct-current (dc) electric field, has been used since the 1930s to dewater soil for construction purposes. This study examines dewatering anaerobically and aerobically digested municipal wastewater solids with applied direct pressure and constant voltage direct current. A pressure filtration apparatus, consisting of a piston and drain plate made of conductive material encased in a body of nonconductive material, was used to apply constant pressure and constant voltage (variable current) during the experiments. Three experimental series were conducted evaluating the effect of polymer dosage and voltage on the final cake total solids; the relationship among pressure, voltage, time, and final cake total solids; and the relationship among initial feed solids and final cake total solids after electroosmotic filtration. Results show that final cake solids were increased to as much as 50% with 60 V de applied. Final cake solids may be enhanced by increasing pressure, voltage, or time, and additional water may be removed from a conventionally dewatered cake by further application of de voltage.