Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370-450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370–450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be: 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and the thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370–450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Improvement of sludge electrodewatering by anode flushing

An improvement of the sludge electrodewatering process is proposed: anode flushing by filtrate recirculation. According to this technique, the mixture of filtrates obtained at cathode and anode sides is used for continuous flushing of the anode chamber of the filter press during electrodewatering. Anode flushing aims to eliminate essential problems of electrodewatering: ohmic heating, rise of electric energy consumption, electrode corrosion, and filtrate contamination. This is attained by better control of the filtrate pH, the filter cake temperature, and the dryness at the anode side, where the physicochemical conditions are most aggressive. The efficiency of the proposed technique is evaluated at lab scale on drilling sludge electrodewatering with and without anode flushing. In experiments without anode flushing, increasing electric current density caused strong increase of anode temperature, desiccation of the filter cake at the anode side, rise of voltage, and significant alkaline contamination of filtrate. The application of anode flushing allowed controlling the electric field strength and temperature. Thus, the dewatering of the sludge has been extended at high electric field without damaging the filter equipment by drastic heating. Furthermore, it reduced filtrate contamination by neutralization of the electrolysis products.     

PRESSURIZED ELECTROOSMOTIC DEWATERING IN A FILTER CYCLE*

This paper describes the role of pressurized electroosmotic dewatering (EOD) in a filter cycle. A laboratory-scale filter-press was used to filter a highly conductive silica suspension under constant pressure, followed by washing and mechanical precompression of the filter cake and finally by pressurized EOD at constant electric current. The influence of filter cycle parameters (filtration and washing pressure and duration, mechanical pressure, and electric field intensity) on the final cake dryness and energy consumption was studied. Electrodes of different materials, forms, and surfaces were used. The optimal conditions of each filter cycle operation were found to minimize the energy consumption during EOD and maximize the cake dryness. With mechanical pressure and electric field intensity increasing, the total energy consumption increased, but the specific energy consumption (per kg of expressed water) decreased, and the final filter cake was dryer. The pressurized EOD also used less energy than thermal drying.

     

PRESSURIZED ELECTROOSMOTIC DEWATERING IN A FILTER CYCLE *

This paper describes the role of pressurized electroosmotic dewatering (EOD) in a filter cycle. A laboratory-scale filter-press was used to filter a highly conductive silica suspension under constant pressure, followed by washing and mechanical precompression of the filter cake and finally by pressurized EOD at constant electric current. The influence of filter cycle parameters (filtration and washing pressure and duration, mechanical pressure, and electric field intensity) on the final cake dryness and energy consumption was studied. Electrodes of different materials, forms, and surfaces were used. The optimal conditions of each filter cycle operation were found to minimize the energy consumption during EOD and maximize the cake dryness. With mechanical pressure and electric field intensity increasing, the total energy consumption increased, but the specific energy consumption (per kg of expressed water) decreased, and the final filter cake was dryer. The pressurized EOD also used less energy than thermal drying.     

PRESSURIZED ELECTROOSMOTIC DEWATERING IN A FILTER CYCLE

This paper describes the role of pressurized electroosmotic dewatering (EOD) in a filter cycle. A laboratory-scale filter-press was used to filter a highly conductive silica suspension under constant pressure, followed by washing and mechanical precompression of the filter cake and finally by pressurized EOD at constant electric current. The influence of filter cycle parameters (filtration and washing pressure and duration, mechanical pressure, and electric field intensity) on the final cake dryness and energy consumption was studied. Electrodes of different materials, forms, and surfaces were used.

The optimal conditions of each filter cycle operation were found to minimize the energy consumption during EOD and maximize the cake dryness. With mechanical pressure and electric field intensity increasing, the total energy consumption increased, but the specific energy consumption (per kg of expressed water) decreased, and the final filter cake was dryer. The pressurized EOD also used less energy than thermal drying.     

Performance evaluation of electrodewatering system for sewage sludges

A laboratory-scale electrodewatering system, incorporating an electric field as an additional driving force to conventional pressure dewatering, has been developed to decrease the water content of sludges generated in wastewater treatment. Consisting of a piston-type filter press, a power supply and a data acquisition system, the electrodewatering system’s performance was evaluated as a function of applied pressure, applied voltage, sludge type and filtration time. Experiments were carried out using sewage sludges with the electric field up to 120 V/cm and pressure ranging from 98.1 to 392.4 kPa. Electrodewatering involving a combination of electric field and pressure enhances both the dewatering rate and final dewatered volume. The final water content of sewage sludges in the electrodewatering system can be reduced to 62 wt%, as compared to 78 wt% achieved with the pressure filtration alone. The electrodewatering system shows the potential to be an effective method for reducing the water content in sludges.     

阴极滤布对活性污泥电渗透脱水的影响(英文)

The mechanical dewatering of activated sludge is troublesome due to its high compressibility of solids. The dewatering can be enhanced dramatically by the use of electroosmosis,in which an electric field is applied to the sludge cake.In this study,the influence of filter cloth on the cathode on the dewatering of activated sludge was investigated.It was found that thicker filter cloth led to lower water removal from the sludge cake,so a stainless steel cathode net with small pore size instead of filter cloth was applied,which improves the dewatering efficiency and reduces the electric power consumption.Moreover,water absorbent materials were helpful to remove the water from the sludge cake.For the electroosmotic dewatering at 7 kPa and 24 V·cm-1,the water content in the sludge cake decreased to 60%(by mass) with the average 0.075 kW·h·kg-1of water removed by using the cathode net.     

Effect of Electro-Osmotic Dewatering on the Quality of Tofu Sheet

As a new dewatering technology with high efficiency and energy saving, electro-osmotic dewatering can be applied to food processing. The objective of this work was to study the effect of combined field dewatering (CFD) involving electro-osmosis and mechanical pressure on the quality of tofu sheet. Combined field dewatering was performed on the dewatering process of tofu sheet for 10 to 30 min at a voltage ranging from 30 to 50 V under various pulse-time ratio (t₊ = 120 s, t_- = 5 s) electric field and 0.047 MPa pressure field. The texture and structure of tofu sheet after treatments were examined by a rheometer and scanning electron microscope (SEM). The result showed that the three quality indexes, i.e., hardness, tensile strength, and ductility of tofu sheet near the anode were 45%, 30%, and 12% higher respectively than those dewatered by common mechanical pressure method. However, those near the cathode were 15%, 25%, and 10% lower respectively. When the electric field was applied for 10 min at 30 V, these indexes reached their maximum values. Meanwhile, the tofu sheet structure near the anode was more compact and homogeneous than that near the cathode. The result indicated that CFD could enhance the quality of tofu sheet.     

水平电场污泥脱水过程

引　言剩余污泥处理是活性污泥法处理污水工艺流程的一个重要组成部分 ,污泥脱水技术的研究旨在提高剩余污泥固含量 ,以降低污泥后处理和再利用的成本 .活性污泥絮凝体中含有大量的水 ,根据水在絮凝体中的位置和功能不同 ,可将其划分为结合水(ｂｏｕｎｄｗａｔｅｒ)、邻位水 (ｖｉｃｉｎａｌｗａｔｅｒ)、毛细管水(ｃａｐｉｌｌａｒｙｗａｔｅｒ)和自由水 (ｆｒｅｅｗａｔｅｒ) [1] .结合水参与形成污泥中生物量 ;邻位水紧贴污泥颗粒表面 ;毛细管水存在于污泥絮凝体的毛细结构中 ;自由水分布在污泥颗粒之间 .这些水与污泥颗粒之间相互作用力…     

Statistical evaluation of hyperbaric filtration for fine coal dewatering

A statistical design of parametric study of pressure filtration for fine coal dewatering is presented. The effects of five major parameters of the dewatering, i.e. applied pressure, filtration time, cake thickness, solids concentration and slurry pH, on cake moisture reduction and air consumption were investigated. The study was conducted starting with two level factorial experiments to identify the most significant parameters, and concluding with response surface methodologies to establish an optimum operating condition for the dewatering of fine coal. It was observed that applied pressure, cake thickness and filtration time were identified to be the key operating variables for reduction of filter cake moisture as well as air consumption. With the key parameters, an optimum condition for the dewatering was determined to be an applied pressure of 93 psi with a cake thickness of 2.5 cm and a filtration time of 4.8 minutes for the laboratory filtration system. At these optimum conditions the filter cake containing about 22 percent moisture by weight and consuming air by 4.1 m³/(m²·min·kg) on dry solid basis was obtained.     

Performance evaluation of electrocoagulation and electrodewatering system for reduction of water content in sewage sludge

Electrocoagulation is applied to sewage sludge as a pretreatment process of an electrodewatering system to reduce the water content of sludge generated in wastewater treatment. The electrodewatering system, by incorporating an electric field as an additional driving force to the conventional pressure dewatering, has been evaluated as a function of an electrode material, applied voltage and filtration time. Experiments were carried out using sewage sludge with a pressure up to 392.4 kPa and applied electrical field ranging up to 120 V/cm. Mass median diameter of the sewage sludge by the effect of electrocoagulation increases from 34.7 μm to the 41.3 μm. The final water content of sewage sludge in the combination of both electrocoagulation and electrodewatering system can be reduced to 55 wt%, as compared to 78 wt% achieved with pressure dewatering alone. The combination of electrocoagulation and electrodewatering system shows a potential to be an effective method for reducing the water content in sludge.     

Control of Sludge-to-Wall Adhesion by Applying a Polarized Electric Field

An application of a polarized electric field to reduce adhesion of a biological sludge to the dryer wall was studied experimentally by contact drying of a sludge cake deposited on a heated metal plate serving as the cathode. It was found that the adhesion intensity is greatly reduced due to a water layer formed at the heated plate, when a fraction of water in the sludge migrates to the cathode by electro-osmosis, as well as by gas bubbles, which are generated by the electrochemical reaction. The voltage gradient from 4 to 5 V/cm was found optimal for drying 10-mm-thick sludge samples. Under these conditions, the electric energy consumption amounted to 3.87 kWh/t. An increase in cathode temperature reduced the sludge-adhering intensity and shortened drying time. The beneficial effect of an electric field on reducing sludge adherence decreases with increasing wall temperature.     

Thermal Dewatering (TDW) to Reduce the Water Content of Sludge

Thermal dewatering describes the process whereby a heating plate and heat supply unit are incorporated into a filter press system to improve separation of water from sludge. The performance of our thermal dewatering system for both wastewater and waterworks sludge was measured and compared with mechanical dewatering in terms of water content, dewatering velocity, cake specific resistance, and energy consumption. Dewatering velocity was improved by a factor of two, cake water content was lower, and specific cake resistance was improved. However, energy consumption was higher. Thermal dewatering systems may be economical and have practical application to improving dewaterability.     

Effect of Cake Compression on the Performance of Centrifugal Dewatering

The effect of cake compression on the centrifugal dewatering is investigated under various rotating speeds and different kinds of cakes. A numerical method is proposed to estimate the capillary pressure and cake permeability under various cake saturations. The most dewatering in this study are operated at the funicular state of cake. The cake permeability decreases, while the capillary pressure increases rapidly, with the decrease of cake saturation during a centrifugal dewatering. The cake saturation can also be simulated once the relations among capillary pressure, cake permeability, and cake saturation are known. The deviations between simulated saturations and experimental data for compressible talc cakes are less than 2%. The centrifugal dewatering of compressible cake includes two mechanisms, the water squeeze due to cake compression and the centrifugal drainage due to pressure difference. The role of cake compression is dominant at the initial 500 s of the dewatering period, and these two factors are almost equal in magnitude as well as in importance when the cake approaches its equilibrium saturation. The porosity and compressibility of cake play the major roles in determining the equilibrium cake saturation. The equilibrium saturation of the compressible talc cake with a lower porosity is much higher than that of incompressible Al₂O₃ cake under a fixed rotating speed. An increase in rotating speed (centrifugal effect) results in a lower equilibrium cake saturation for either compressible or incompressible cakes; however, the increase in rotating speed is more efficient for an incompressible cake in the centrifugal dewatering.     

煤气化细渣陶瓷膜真空脱水试验与数值模拟

气化细渣是煤炭气化过程的废弃物,高效脱水是其资源化利用、减量化处置的必要前提。本文采用陶瓷膜真空过滤系统开展了脱水实验并对脱水过程进行了数值模拟。气化细渣料浆浓度和液下吸附时间影响滤饼厚度且滤饼厚度增加导致水分运移路径增长,使得有效脱水时间增加;滤饼脱水过程的脱水速率值呈现非线性降低趋势且滤饼水分极限值为40%,这与气化细渣物化性质有关;真空度>0.08MPa时气化细渣滤饼中“通道水”能够在约24s有效脱除。Fluent数值模拟过程选用了欧拉模型并确定了陶瓷膜滤板和气化细渣滤饼的阻力系数,脱水过程的实验值与模拟结果误差小于5%,证实了模型可靠性。模拟过程分析了气化细渣脱水过程中压力场和水分含量分布云图的演变规律,结果表明,增加脱水系统真空度、降低滤饼厚度、提高“通道水”比例以及增大气化细渣颗粒等效当量直径能够提高气化细渣脱水效率。此外,陶瓷膜真空脱水过程所得滤液洁净度高且部分指标达到了工业用水的标准。     

WATER REMOVAL FROM SLUDGE IN A HORIZONTAL ELECTRIC FIELD

A new method for sludge dewatering was proposed, in which a horizontal electric field was applied in order to facilitate the dissipation of gases produced at electrodes and to keep the anode soaked in water during the dewatering process. The effects of operation conditions such as the magnitude of electric field strength, pH of aqueous phase, the pretreatment procedures including flocculation, freezing and heating on the water removal were examined, respectively. The morphological difference between the concentrated sludge produced by electrodewatering and by vacuum filtration was revealed with scanning electron microscopy, which shown that electrodewatering was effective in removing the capillary water in the sludge floc. At electric field strength of 1200 V/m, the sludge concentration could be increased from 3 to 8%(w/w), indicating that over 60% of water was removed from the sludge. Compared to those operated in a vertical electric field, the method described in the present study has the advantages in terms of high eficiency, simple structure and ease of operation.     

WATER REMOVAL FROM SLUDGE IN A HORIZONTAL ELECTRIC FIELD

A new method for sludge dewatering was proposed, in which a horizontal electric field was applied in order to facilitate the dissipation of gases produced at electrodes and to keep the anode soaked in water during the dewatering process. The effects of operation conditions such as the magnitude of electric field strength, pH of aqueous phase, the pretreatment procedures including flocculation, freezing and heating on the water removal were examined, respectively. The morphological difference between the concentrated sludge produced by electrodewatering and by vacuum filtration was revealed with scanning electron microscopy, which shown that electrodewatering was effective in removing the capillary water in the sludge floc. At electric field strength of 1200 V/m, the sludge concentration could be increased from 3 to 8%(w/w), indicating that over 60% of water was removed from the sludge. Compared to those operated in a vertical electric field, the method described in the present study has the advantages in terms of high eficiency, simple structure and ease of operation.     

液力过滤与液力压密脱水的理论(一)

将滤室固定不变的板框或箱式压滤机的操作过程分成滤饼过滤阶段和液力压密脱水阶段两个过程来研究。在滤饼过滤阶段 ,应用表面过滤机理 ,采用传统的鲁思过滤基本方程和平均过滤比阻的理论进行研究。在液力压密脱水阶段 ,应用达西定律建立了液力压密基本微分方程 ,根据研究得出滤饼渗透系数与孔隙率在压密脱水阶段的线性取代关系的结论 ;滤室固定的限制条件和物料平衡条件 ,推导出液力压密的脱水方程式。分析了影响液力压密脱水的时间因素和液力压密速率的各操作参数。建立了完整的液力过滤和压密脱水理论 ,为自动压滤机的设计提供了理论指导