Influence Of Electric Control Mode On Electro-dewatering Performance And Optimization Research Of Sludge

For sludge electro-dewatering?EDW?technology,current and voltage are the most direct and key factors affecting its dehydration performance.By adjusting the electronic control mode during the electro-dewatering process,the dewatering effect can be directly improved without changing the sludge properties or adding foreign substances,and is suitable for most sludges.Therefore,this study discussed the influence of electric control mode on sludge electro-dewatering effect by changing the operating conditions of two electric control modes,namely,a single constant current mode and a constant current and constant voltage combined mode,and combining with the filtrate flow rate,temperature rise rate,final dry solids content,unit energy consumption and other aspects in the dehydration process.At the same time,because it is difficult to remove the bound water in cells by traditional electro-dewatering,and low-temperature pretreatment can break sludge cells and extracellular polymeric substances?EPS?to release internal water,the feasibility of low-temperature pretreatment to improve sludge electro-dewatering efficiency was investigated.The main experimental conclusions are as follows:?1?Under constant current mode?C-EDW?,the dry solids content growth rate of sludge electro-dewatering remains stable,and increases with the decrease of initial dry solids content and sludge thickness and the increase of current intensity.The final dry solids content after dewatering increases with the decrease of initial dry solids content and sludge thickness and the increase of mechanical pressure.Under constant current mode,the final dry solids content of sludge was reduced to 48.7%after electro-dewatering with the optimal process parameters:current density 1.4A,mechanical pressure 31.4kPa,sludge thickness 8mm,and initial dry solids content 18.5%.The unit energy consumption of electro-dewatering was 0.135⁰.269kW·h·kg^-1_waterater under constant current mode,on which the initial dry solids content of sludge had the greatest impact.When the initial dry solids content increased by 2%,the unit energy consumption required for sludge electro-dewatering is reduced by about 0.05 kwh/kg_waterater on average.?2?Compared with the C-EDW,the electro-dewatering of sludge in constant current-voltage mode?CV-EDW?has the advantages of high final dry solids content,low heating rate and low unit energy consumption.The final dry solids content and unit energy consumption increase with the decrease of current level in constant current stage or the increase of voltage level in constant voltage stage.Compared with the constant voltage mode?V-EDW?,the constant voltage-current mode?VC-EDW?significantly improves the sludge dewatering rate,and the final dry solids content increases with the decrease of the current level and voltage level.However,the unit energy consumption of dewatering under the two modes is small,both of which are 0.132⁰.163 kWh/kg_water,and are mainly affected by the voltage level in the constant voltage stage.When the voltage level is decreased by 10 V,the unit energy consumption is reduced by an average of 27.15±1.77%on average.Compared with CV-EDW,the dehydration rate of VC-EDW is increased by 72.9%on average.However,the unit energy consumption required for dehydration increases by 43.09%when the dry solids content is less than 45%.?3?Compared with the sludge without low-temperature pretreatment,the SCOD,NH₃-N and electrical conductivity of the sludge were significantly improved after low-temperature heat treatment,and with the increase of the pretreatment temperature,the SCOD concentration increased and the NH₃-N concentration decreased.The filtrate flow rate and final dry solids content of the pretreated sludge were not significantly improved during electro-dewatering process.When the dry solids content of the sludge is lower than 43%,the heating rate and unit energy consumption of the sludge after low-temperature heat treatment are significantly lower than that of the sludge without low-temperature pretreatment during electro-dewatering,and the heating rate and unit energy consumption decrease with the increase of the pretreatment temperature.When the dry solids content of the sludge is higher than 43%,the temperature rise rate and unit energy consumption of sludge after low-temperature pretreatment will rise sharply during electro-dewatering,even exceeding that of the sludge without low-temperature pretreatment.When the dry solids content of the sludge is 40%,the dehydration energy consumption is reduced by about 0.01 kWh/kg_waterater for every 10?increase in the pretreatment temperature.