Research On Safety And Stability By Electro-dewatering For Sewage Sludge

Sludge dewatering is a paramount process in wastewater treatment system as itrelates to the costs for sludge disposal downstream and the value of utilization.Currently, the thermal drying method and plate&frame type filter were widely used,however, problems to the former method was high capital and operating costs, thelatter method was increase the dry weight of the sludge. Based on the surface chargeof the sludge, by the action of the electric force, the water separated from the sludgeparticles to achieve the purpose of dehydration, electro dewatering as a newsolid-liquid separation technology has been paid attention. In this article, with a focuson safety and stability by electro dewatering technology of sewage sludge, as well asthrough the study of the change of heavy metal and microorganisms in sewage sludge,in order to make a comprehensive evaluation of electro dewatering technology onsewage sludge for future reference.Through comparing of the heavy metal content of sewage sludge and afterelectro dewatering, the results show that when the anode is using graphite (inert)material, when the graphite plate (inertia) was used as the anode, after electricdewatering, the heavy metal content of the sludge was lower than the original content.These results indicate that electro dehydration can cause the heavy metal content inthe sludge to be reduced, allowing for the separation of heavy metal in sludge. Whenthe operating voltage is40V, the percentages of separation achieved by Cr, Ni, Zn, Cuand Pb in the sludge were10.79%,9.47%,7.29%,16.64%and14.04%respectively. Itconfirmed that the common metal anodes can be caused a large amount of corrosionin the process of electro dewatering. After electro dewatering, the content of Cr, Niand Cu were high increased in the sludge; with the iridium plating titanium plate asthe anode, the results with the inert electrodes (graphite plate) were basic identically,and no corrosion occurred, the content of heavy metal in the sludge was reduced. Theuse of the iridium plated titanium plate also had no negative impact on the sludgedehydration.By comparing the experimental results of the total number of bacteria in thesewage sludge before and after electro dewatering, analysis the effect and the changesof bacteria in the sewage sludge by electro dewatering technology. The results show that the working voltage of30V, the total number of bacteria in sewage sludge wasreduced by33.13%; compared to the raw sludge40V for working voltage, the totalnumber of bacteria in sewage sludge was reduced by54.07%; with comparing of thesewage sludge before and after electro dewatering, when working voltage was50V,the total number of bacteria was reduced by67.97%. It has inactivation ofmicroorganism in sewage sludge after electro dewatering, and the inactivate effect ofanode area was greater than the sludge of cathode area.Experiments were measured on the properties and index of the electrodewatering filtrate, including pH, COD, suspended solid (SS), total nitrogen (TN) andheavy metal content. Through the experiment, it ware found that the pH of electrofiltrate was11.92, the value of the total nitrogen was375.6mg/L, COD value was1800mg/L, the water samples must be treated to meet the standard to discharge; TheSS of electro dewatering filtrate were increased with the increased voltage; the heavymetal content in electro dewatering filtrate and the heavy metal content in the sewagesludge were correspondence, and both satisfied with the effluent standards.