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.     

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.     

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.     

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…     

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.     

THE ELECTRODEWATERING OF SEWAGE SLUDGES

Electrodewatering (EDW), the enhancement of conventional pressure filtration by an electric field, is an emerging technology with the potential to improve dewatering especially for difficult materials. CSIRO has many years of experience in EDW, ranging from bench scale tests to demonstration trials. A recent programme has investigated the applicability of EDW to aerobic wastewater treatment sludges which are particularly difficult to dewater using conventional equipment.

The bench scale filtration experiments produced cakes with solids contents of 35-46 wt% using EDW, compared with 24-30 wt% using pressure filtration alone. This paper : • describes how the dewatering results were achieved;

•identifies a relationship between moisture removal limits by EDW and the forms of water within the sludge;

•shows the results of preliminary attempts to mathematically model the EDW process     

THE ELECTRODEWATERING OF SEWAGE SLUDGES

ABSTRACT

Electrodewatering (EDW), the enhancement of conventional pressure filtration by an electric field, is an emerging technology with the potential to improve dewatering especially for difficult materials. CSIRO has many years of experience in EDW, ranging from bench scale tests to demonstration trials. A recent programme has investigated the applicability of EDW to aerobic wastewater treatment sludges which are particularly difficult to dewater using conventional equipment.

The bench scale filtration experiments produced cakes with solids contents of 35-46 wt% using EDW, compared with 24-30 wt% using pressure filtration alone. This paper : ? describes how the dewatering results were achieved;

?identifies a relationship between moisture removal limits by EDW and the forms of water within the sludge;

?shows the results of preliminary attempts to mathematically model the EDW process     

Experimental Study on Thermal Hydrolysis and Dewatering Characteristics of Mechanically Dewatered Sewage Sludge

After mechanical dewatering, sewage sludge has a moisture content of around 80 wt% and further disposal is required. A new sewage sludge semi-drying (dewatering) process is proposed and verified. It combines thermal hydrolysis and subsequent mechanical dewatering, with less energy consumption than traditional thermal drying. Sludge treated using this new process satisfies further disposal requirements (e.g., landfill or autothermal incineration). In the present study, a high-pressure test reactor was used to study the thermal hydrolysis of dewatered sludge. Thermally hydrolyzed sludge was subsequently dewatered by centrifugal sedimentation or by pressure filtration. The amount of organic compounds returning to the water phase was also measured. According to the results from centrifugal settling tests, the optimal thermal hydrolysis treatment temperature was 180°C. The moisture content then dropped to 1.44 kg/kg dry solids (DS; 59 wt%) after dewatering under relative centrifugal force of 9,000 × g from 5.67 kg/kg DS (85 wt%). Pressure filtration further reduced the moisture content of filter cakes to only 0.5 kg/kg DS (33 wt%, hydrolysis temperature 180°C). After thermal hydrolysis, the heating value of sludge (moisture-free basis) was about 80% that of the untreated sludge.     

Dewatering of Sewage Sludge

Dewatering of sewage sludges is usually carried out using belt filter presses or centrifuges. The ability to remove water from sludges by mechanical dewatering is a property of both the sludge and the equipment used for dewatering. Newer high-solids centrifuges can remove more water than a belt press but require a higher chemical conditioning dose. The Gt value, the product of the mean velocity gradient and the shear time, has been found to be a useful parameter for characterizing the shear in mechanical dewatering equipment. Dewatering can be considered a two-step process, filtration followed by expression. The expression step is the most important of these and the benefits of various sludge processing techniques and conditioning chemical types remains a fruitful area of research.     

Dewatering of Sewage Sludge

Dewatering of sewage sludges is usually carried out using belt filter presses or centrifuges. The ability to remove water from sludges by mechanical dewatering is a property of both the sludge and the equipment used for dewatering. Newer high-solids centrifuges can remove more water than a belt press but require a higher chemical conditioning dose. The Gt value, the product of the mean velocity gradient and the shear time, has been found to be a useful parameter for characterizing the shear in mechanical dewatering equipment. Dewatering can be considered a two-step process, filtration followed by expression. The expression step is the most important of these and the benefits of various sludge processing techniques and conditioning chemical types remains a fruitful area of research.     

ULTRASOUND IN THE SUSPENSION SEPARATION METHODS

Investigations were carried out on the effect of the ultrasonic field and some selected chemical compounds on the process of preparing sludges to be dewatered by mechanical devices.

The tests; were performed in a laboratory on real sludges. The processes occurring in sludges due to presence of ultrasonic field and applied chemical reagents were determined on the basis of a commonly used method of determining the sludge dewatering, in both filtration and sedimentation.

The interdependences of value changes of the above mentioned factors and the possibilities of applying ultrasonic waves to intensifying sludge dewatering process were examined. The obtained results confirm the applicability of ultrasonic waves to the process of sludge treatment and prove that the initial assumptions concerning the use of ultrasonic field in the suspension separation methods to be valid.     

ULTRASOUND IN THE SUSPENSION SEPARATION METHODS

Investigations were carried out on the effect of the ultrasonic field and some selected chemical compounds on the process of preparing sludges to be dewatered by mechanical devices.

The tests; were performed in a laboratory on real sludges. The processes occurring in sludges due to presence of ultrasonic field and applied chemical reagents were determined on the basis of a commonly used method of determining the sludge dewatering, in both filtration and sedimentation.

The interdependences of value changes of the above mentioned factors and the possibilities of applying ultrasonic waves to intensifying sludge dewatering process were examined. The obtained results confirm the applicability of ultrasonic waves to the process of sludge treatment and prove that the initial assumptions concerning the use of ultrasonic field in the suspension separation methods to be valid.     

Gewinnung von Brennstoff für Kraftwerke aus Klärschlamm

Production of a combustible for coal-fired power stations based on sewage sludge . This article describes various means of achieving more extensive mechanical dewatering of sewage sludges. The heat content of the sludge solids can become available for combustion processes. The sludge filter cakes obtained by the “CarboSed” process can be disposed of with minimum energy consumption by fluidized bed combustion or be used after appropriate work-up as a combustible in coal-fired power stations with full exploitation of their heat content for generation of steam and electric current. Partial substitution of primary energy sources such as coal and fuel oil by sludge filter cake is feasible in all cases. The processes thus make a contribution to the saving of energy resources and the disposal of sludge.     

Dewatering behaviour of water treatment sludges associated with contaminated site remediation in Antarctica

Sludge reduction and dewatering is an important aspect of water and waste water treatment. This is especially true in the case of Australia's Antarctic contaminated site remediation program, where the reduction in volume of wastes to be returned to Australia can lead to significant transport and handling cost savings. The dewatering characterisation of water treatment sludges from an Antarctic contaminated site was conducted using a theory of suspension dewatering developed by Buscall, Landman and White. This theory uses fundamental material properties of compressibility and permeability to determine the diffusivity of a suspension. Diffusivity is a useful property that can be used to directly compare the dewaterability of various sludges. In this investigation, several water treatment sludges were collected and characterised in the field to determine the impact of temperature and additives on compressibility, permeability and diffusivity. The Antarctic sludges were found to be less compressible and less permeable than materials such as mineral suspensions and alum water treatment sludges. Compressibility was found to decrease with the addition of powdered coagulation aids such as bentonite and chitosan.     

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.