Research On Sewage Sludge’s Characteristics Of Electro-dewatering Assisted By Adsorptive Material And Device Development

Based on the characteristics of charges on sludge surface, the electro-dewateringtechnology separates the water from sludge particle by the effect of the electric fieldforce, which achieves the purpose of dehydration. The paper focused on the way toseparate water from sludge. That is converting the gravity separation way toadsorption separation way using adsorbent material beneath the cathode to improvethe efficiency of dehydration. By adding adsorbent material, the water dewatered fromsludge was separated from electrode quickly, and the obstacle to subsequent waterremoved was weakened.By adding adsorbent materials, the final water content of sludge and the energyconsumption of electro-dewatering process were lower than that of no adsorbentmaterials. Meanwhile, the effects of applied voltage, mechanical pressure anddifferent cathode on sludge electro-dewatering process after adding adsorbent materialwere also studied. The experiment showed that for sewage sludge cake thickness of5mm, there was an optimal voltage between40V and50V. With the increasing ofmechanical pressure, the final water content decreased at first and then kept constant,and the best dehydrating effect appeared when the pressure was21kPa. The betterdehydration effect was obtained when the stainless steel net of pore diameter of58μm(250mesh) was used as cathode, also this cathode might play the role of filter cloth.The best operation condition obtained was that50V,21kPa and the58μm（250mesh）stainless steel net as cathode. And in this condition, the water content of sludgedecreased from82.7%to56.1%in90seconds, and the energy consumption was186kWh per ton wet sludge.Improvement was made based on the existing electric dehydration equipments’disadvantages, and two kinds of sludge dewatering equipments were developed.Through the practical application, it was found that sludge electro-dewateringequipment of circular electric field and pressure synergy not only avoided thephenomenon of electrodes’ deformation under pressure, but can remove the water inthe sludge rapidly and effectively due to slow current attenuation process. But someproblems still need to be settled, such as the rolling resistance was too big anddewatering time was too short. In order to optimize the operation unit for sludge treatment, three kinds of sludgetreatment schemes were designed: the scheme Ⅰ was that first sludge was dried tomoisture content of20%, then burned and the heat of incineration was used tosludge-drying; the scheme Ⅱ was that through the electro-dewatering, the sludge wasdewatered to water content of70%, then dried to moisture content of20%, finally itwas used for incineration power generation; the scheme Ⅲ, analogous to the schemeⅡ, through the electro-dewatering, the water content of the sludge was decreased to65%, then dried to20%, finally it was used for incineration power generation. Bycomparing the energy consumption of these three different schemes, it was found thatscheme Ⅰcouldn’t achieve its own system energy balance and needed extra energysupplement everyday; scheme Ⅱ and Ⅲ could not only achieve its own energybalance, but also could output some thermal energy. Scheme Ⅲ output much moreenergy than scheme Ⅱ.