Research On Electro-osmotic Dewatering For The Sewage Sludge Cake After Mechanical Dewatering

With the rapid increase of sludge production and the more stringent regulations forthe treatment and disposal of sludge in China, it needs to use a cost-effective technologyfor the further dewatering of sludge so as to reduce the volume of sludge. In this paper,we used the sludge after mechanical dewatering for the research. The effectiveness ofthe electro-osmotic technology for the further dewatering of sludge was validated, andthe operating parameters were optimized. In addition, the characteristics of sludge cakeand removed water after electro-dewatering under different voltage gradient werestudied, and the change of sludge’s characteristics on the performance ofelectro-dewatering was also discussed in this paper.The use of electro-osmotic dewatering technology could reduce themoisture content of sludge to less than60%so as to meet the requirement forlandfilling and agricultural using in China. During the electro-osmoticdewatering process, the role of mechanical force was to ensure the close contactbetween electrode and sludge, and76kPa was suitable. With the increase ofvoltage gradient, the dewatering rate in the initial phase and the energyconsumption were both increased. But for the consideration of dewateringefficiency and energy consumption, the voltage gradient of30V/cm was thebest. At the same voltage gradient, the dewatering efficiency could be the bestwhen the thickness of sludge cake was1.0cm. From the perspective ofdewatering efficiency and energy conservation, the optimal operating conditionsfor the electro-dewatering of sewage sludge were determined to be themechanical pressure of76kPa, the voltage gradient of30V/cm, and the sludgethickness of1.0cm. In addition, compared with the use of titanium plate anodeand stainless steel plate anode, the coated titanium anode had betteranti-corrosion and dewatering efficiencies.During the electro-osmotic dewatering of sludge, the electrolysis of watercould occur in the area of electrodes so that H+would generate near the anodeand OH-would generate near the cathode. Because of the action of theelectro-migration, the positively charged substances could move to the cathode and the negatively charged substances could move to the anode. Therefore, afterthe electro-osmotic dewatering, the moisture content, volatile substancescontent, pH, conductivity, as well as some of the metal ion contents of sludgewould have some changes. And the pH, conductivity, COD, ammonia nitrogenand total phosphorus of removed water would also change under differentvoltage gradient.The effect of the conductivity of sludge on the dewatering efficiency andenergy consumption were evaluated via adjusting the conductivity using Na2SO4adding and deionized water washing, and the results showed that theconductivity of sludge would have little influence on electro-dewatering, but theenergy consumption would increase significantly after the adding of Na2SO4anddecrease after the deionized water washing. After the pretreatment of excesssludge by ultrasonic technology, the bound water content, zeta potential, organicmatter content in the water increased, but the particle size decreased. After thepretreatment of excess sludge by ozonation technology, the bound water content,zeta potential, particle size would be reduced, but the organic matter content inthe water increased. In addition, after the pretreatment by ultrasound and ozone,the electro-osmotic dewatering efficiency of sludge would be reduced and theenergy consumption of electro-dewatering would increase.