Research On Mechanism And Application Of Sludge Electro-dewatering Based On The System-wide Conductance

Effective solid-liquid separation is the key in the disposal of treatment and disposal of municipal excess sludge.The electro-dewatering(ED)is a solid-liquid separation technology,with a high efficiency,energy saving,effective preservation of organic matter.It can achieve the deep dewatering of the mechanical dewatered sludge,which creates favorable conditions for the subsequent disposal and utilization of the sludge.The dynamic characteristics of each potential function region in the process of ED were studied by combining theoretical analysis and experiments.The characteristics of solid-liquid separation and electric field in the process of ED were studied.The influence mechanism of core structure configuration on sludge ED characteristics was systematic research.Based on the continuous running experiments,the failure mechanism of core structure which affects the long-term stable operation of sludge dewatering technology is discussed.Through the analysis of the system-wide conductance process of sludge ED,it was found that the anode drying layer potential Uca depends on the volume fraction of the dispersed phase under the condition of reaching the ultimate minimum water content,and there is an equation relationship between Uca and the solid content.There is a relationship between Uca and sludge layer potential Us and the increase of Uca reduces the effective electric field intensity Eed,which is the main reason for the lack of dehydration power.Through the analysis of solid-liquid separation characteristics and energy consumption of sludge ED,it was found that under the conditions of 40%solid content,1 cm sludge thickness,20 V·cm-1 electric field intensity and 100 kPa mechanical pressure,the average energy consumption for dehydration was 0.122 kWh-kgdewater-1,about 20%of the energy consumption for heat drying.Taking energy consumption and equipment processing capacity as the evaluation targets,the important indexes for evaluating the efficiency of ED technology were proposed from the perspective of unit dehydration energy consumption(WED’filt)and unit anodic processing capacity(QED’filt).A quadratic equation dynamic model with WED’filt and QED’filt as the dynamic factors was established,which described the effects of voltage and mechanical pressure on energy consumption per unit dehydration and per unit anodic capacity.The results of response surface optimization showed that the model fits well with the experimental data.The core structure configuration and separation mechanism of sludge dewatering were studied,it was found that the processing capacity of the three-dimensional wave anode was 17.8%higher than that of the conventional plane in the ED with the same dewatering degree and energy consumption.The effects of sludge solids,water distribution,sludge potential distribution and electrode surface current distribution(based on COMSOL secondary current model)on WED’filt,QED’filt and electrical dewatering performance coefficient(KsiED)were studied,it was showed that the wave anode could increase the electrochemical reaction strength and increase the electroosmosis flow by increasing the electrochemical reactive point.The characteristics of gas producing and discharging by anodic oxygen evolution during ED were explored,it was found that the gas emission ratio during the dewatering process of the wave surface anode was 0.28,which was higher than 0.08 of the plane electrode.The reason maybe that oxygen evolution reaction gas was easy to be discharged from the upper convex low-stress region of the wave surface anode,so the influence of gas barrier layer on the contact between anode and sludge cake was reduced.By investigating the factors influencing the stability of the continuous operation of ED,it was found that the main reason for the decline of the electric energy input was the decrease of the electric contact caused by the alkaline scaling of the cathode during the 15 d continuous operation of the ED pilot plant.Therefore,the method of increasing mechanical pressure was proposed to control the filter flow rate and the alkaline environment in the cathode area,which reduced the scaling rate of the cathode by about 10.1%and the installed capacity by about 27.7%.The mechanical descaling method can effectively control Usc and realize the batch dewatering time of less than 8 min,the anode utilization rate of 93.8%,and the long-term stable operation of the sludge at a temperature below 65℃.By analyzing the material and energy flow of the full proportion ED system,it was found that the energy consumption of ED accounts for 92.3%of the total energy consumption of the whole dewatering system.The driving force characteristics of the application technology of ED were analyzed,and found that one of the main reasons restricting the application of this technology was that the application structure was difficult to effectively match the mechanical pressure and electrical parameters,which leads to the difficulty in optimizing WED’filt and QED’filt under working conditions.Based on the experimental results and the dynamic analysis of the conductance process,the multilayer vertical electric field intermittent batch ED system was developed to realize the long-term stable operation under the condition that the WED’filt was 0.133 kWh-kgdewater-1,QED’filt was 40.6 kgdewater·m-2·h-1 and the separation efficiency was 97.1%.