Performance Analysis Of Sludge Electro-osmotic Dewatering Under Constant Electric Field And Pulsed Electric Field

With the rapid development of China's economy,the demand for sewage sludge production,treatment and disposal is increasing day by day,and the environmental protection policy pursued by the state is becoming stringently.So how to reduce the harm of municipal sludge and make use of it has become a subject of great concern in related fields.The premise of sludge treatment and disposal is to reduce the water content of sludge.As a new sludge dewatering technology,electro-osmotic dewatering technology(EDW)has the characteristics of strong dehydration and energy saving.In this paper,the research object is wet sludge with water content of82.74%,which has been dewatered by mechanical pressure in municipal sewage treatment plant.This experiment analyzed the influence of voltage gradient on sludge dewatering performance,removal efficiency of organic matter and heavy metal elements,and selected the optimal voltage of electro-osmosis by the analysis of energy consumption economy.Then the effect of duty cycle of pulse signal on dewatering capacity of sludge electro-osmosis process was studied,it is concluded that the performance of sludge dewatering can be further improved by applying pulsed electric field.In addition,cut the sludge into three layers,to analysis the migration with time and space about water content,pH,zeta potential,conductivity and volatile organic matter content in sludge.The results show that increasing the electro-osmotic voltage can effectively reduce the water content of sludge.When the voltage exceeds 30 V,the increasing trend of sludge dewatering performance slows down.And the pH of the filtrate also showed similar change law.When the voltage is between 0V and 10 V,the COD value of filtrate decreases,as the voltage continues to rise,COD gradually rises.The voltage gradient of electro-osmotic has affected the removal of Cu,Cr,Zn and Pb.Among them,the removal effect of Cu and Pb is better,the removal effect of Cr and Zn is weaker,but that of Cd and Ni is not obvious.Considering the dehydration effect and energy consumption,the optimum voltage is 30 V.Adjusting duty cycle of pulsed electric field can promote sludge dewatering performance,but the effect of adjusting pulse frequency has no obvious improvement,and when the duty cycle is about 50%,the electro-osmotic dewatering effect is the strongest.When the duty cycle is between 40% and 60%,the sludge water content can be reduced to less than 60% to meet the needs of post-treatment and disposal.Under pulsed electric field,the distribution of water in sludge is more uniform and the resistance of sludge is relatively small,and the current through the sludge cake fluctuates strongly.The energy consumption of electro-osmotic dehydration is much lower than that of thermal drying at the same level.Under the experimental conditions,when dried 1t wet sludge to 58.2% water content by different methods,energy consumption is lowest when duty cycle is 60%.The energy consumption of electro-osmotic dewatering at 60% duty cycle is 28.12% less than that of constant electric field electro-osmotic dewatering at the same voltage,and the water content of sludge has decreased by 5.3%.This shows that adjusting the duty cycle of pulsed electric field can promote the dewatering performance of electro-osmosis and greatly reduce energy consumption.Experiments show that water in sludge moves from anode area to cathode area under electric field and discharges from cathode,which is related to the change of sludge pH value and zeta potential.The decrease of sludge pH in the anode area leads to the decrease of zeta potential absolute value of sludge cake.This will increase the degree of colloidal polymerization of sludge and inhibit electro-osmotic dewatering,and the change of cathode area is opposite.Both constant electric field and pulsed electric field electro-osmosis can inhibit the dewatering in the anode region,however,the suppression level of pulsed electric field on the dewatering effect in the anode region is lower,and the overall dewatering performance of the sludge cake is strengthened.The conductivity changes with the migration of charged particles.The conductivity in the anode region is the highest,followed by the cathode region and the lowest in the middle region.