Sludge dewatering by electrokinetic technique: effect of processing time and potential gradient

A sludge cake (87.8% of moisture content) from a wastewater treatment plant was used to investigate the effects of processing time and potential gradient on the water removal by an electrokinetic (EK) process. A potential gradient ranging from 2.5 to 5.0 V/cm was applied to induce the movement of bound water within the sludge specimen for a time period of 4-41 h. Results showed that the direction of electroosmosis (EO) flow was from the anode to cathode. Due to the release of HI and OH- through electrolysis of water, the sludge pH was maintained at 2.4-6.6 near the anode side and 8.7-10.7 near the cathode after EK treatment. At an applied potential gradient of 5.0 V/cm for 41 h, the moisture content of sludge decreased further to 62.6%. The EO permeability and the power consumption throughout the test period were approximately 0.24-1.38x10(-5) cm(2)/V s and 11.5-249.7 kW h/m(3), respectively. A total disposal cost saving of up to 17.4-25.6% was achieved with the aid of the EK technique. Results also showed that increasing either the potential gradient or the processing time would enhance the sludge dewatering efficiency. (C) 2002 Elsevier Science Ltd. All rights reserved.