Electroosmotically enhanced sludge pressure filtration

Wastewater sludge is routinely dewatered to lower the cost of transportatio n and disposal. Dewatering is achieved via vacuum filtration, centrifugatio n, sand beds, and belt filter presses. Electroosmosis, the movement of wate r in the influence of a direct-current (dc) electric field, has been used s ince the 1930s to dewater soil for construction purposes. This study examin es dewatering anaerobically and aerobically digested municipal wastewater s olids with applied direct pressure and constant voltage direct current. A p ressure filtration apparatus, consisting of a piston and drain plate made o f 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 ef fect of polymer dosage and voltage on the final cake total solids; the rela tionship among pressure, voltage, time, and final cake total solids; and th e relationship among initial feed solids and final cake total solids after electroosmotic filtration. Results show that final cake solids were increas ed to as much as 50% with 60 V de applied. Final cake solids may be enhance d by increasing pressure, voltage, or time, and additional water may be rem oved from a conventionally dewatered cake by further application of de volt age.