Electro-dewatering of sludge under pressure and non-pressure conditions.

The electro-dewatering method is regarded as a promising approach to reduce the water content in sludge. Laboratory scale non-pressure and pressure-driven dewatering reactors were set up to study the dewatering rate in different types of sludge and the water content in the final sludge cake after electro-dewatering process. It was observed that in non-pressure experiments, the water removal rate was highly dependent on sludge pH buffering capacity and the type of sludge; the highest water removal rate (83.2 lm(-2) day(-1)) was achieved with anaerobic sludge. When pressure was applied, the rate of removal of water from the anode and the cathode depended on alkalinity as well as current density. During the electro-dewatering process, pressure had a significant contribution to water reduction in the final sludge cake in experiments using raw sludge and raw sludge with added alkalinity in comparison with non-pressure experiments using the same types of sludge. However, experiments using anaerobically digested sludge in non-pressure and pressure-driven reactors resulted in the same water content in the final sludge cake (40%). In general, different types of sludge with various amounts of alkalinity affected sludge electro-dewatering capacity by changing zeta potential and pH. Migration of negatively charged organic substances occurred during the applied low-level direct current (15 V), and chemical oxygen demand and total organic carbon concentrations in removed water were found to be higher at the anode and lower at the cathode in comparison with control experiments.