Electro-Osmotic Dewatering (EOD) of Bio-Materials
- 1.7k Downloads
In practical application of electro-osmotic dewatering (EOD), it is very important to increase the dewatering rate, and to decrease the final water content and the electric power consumption for water removal. In a batch apparatus for dewatering operation of colloidal suspensions or sludges, electric power applications, such as alternating current (AC) electric field and interrupted or intermittent electric field, and also arrangements and configurations of the electrode in contact with the suspension or sludge can be available for improving the performance of electro-osmotic dewatering. The effects of these electric field applications and the electrode arrangements and configurations on the dewatering processes are shown, and the usage of electro-osmotic dewatering is focused to biomaterials such as sewage/activated sludge, waterworks sludge, food processing products and wastes, and biomass sludge.
KeywordsSewage Sludge Alternate Current Water Removal Electric Power Consumption Specific Electric Conductivity
For applying EOD practically to various kinds of materials, it is important essentially to increase the dewatering rate, and to decrease the final water content and the electric power consumption for water removal, as much as possible. From these points of view, various applications of electric field, which are different from continuous DC condition, have been attempted to improve the performance of EOD. In order to reduce the negative effect for dewatering, which is characteristic of EOD, such as the increase of electrical contact resistance mentioned above, many investigations have been carried out for better and higher performance of EOD.
The mechanism of EOD is different from that of such widely used dewatering processes as mechanical methods using fluid pressure, compressive and centrifugal forces. EOD has some advantages compared with mechanical dewatering methods, and it can be more effective for solid–liquid mixtures consisting of colloidal particles and gelatinous and biological materials that are not successfully dewatered by mechanical methods. EOD has been applied to numerous materials, mainly inorganic materials such as peat, clay, soil, coal, cement, concrete, metal and hydroxides (Rampacek 1966). EOD for clay slurries and washed mineral sludges has been examined for over a century. Referring to biomaterials, EOD has been used for dewatering of waterworks and sewage sludges, food processing wastes, biological wastes, and biomass sludges.
R&D on EOD carried out in the last two decades is described in this chapter. This overview includes various published applications of electric field for processing EOD which are expected to be available for enhancing the performance of EOD are shown in terms of water removal and energy consumption.
2 Theoretical Backgrounds
2.1 Recent Theoretical Developments
Equation (7) suggests that the e- and the p S -distributions are not uniform numerically at the final stage of dewatering, and that e at the drainage surface does not change; that is, the initial value of e is maintained during dewatering and p s becomes a maximum value near the upper electrode opposite to the drainage surface.
In this equation, p S,i is the pre-consolidation pressure, and ω 0 , the total mass of solid particles per unit cross-sectional area of the bed.
Here L is the thickness of the bed in the dewatering process, and L i and L f , the initial and the final thicknesses of the bed, respectively. C e and E pg in Equations (9–10) are determined based on experimental data. Thus, for the process of EOD under constant electric current, the time evolutions of L, the p S - and the e-distributions in the material are estimated from Equations (12–13).
2.2 Principles for High Performance EOD
As described previously in the Section 1, the water content near the upper electrode opposite to the drainage surface is locally reduced during EOD, resulting in increase of electrical contact resistance between the electrode and the material being dewatered. The specific electric conductivity, λ?, of the material is ordinarily decreased with decreasing water content, and then such a circumstance enhances the increase of the electrical contact resistance. Consequently the efficiency of EOD is reduced markedly.
For high-performance EOD, it is advisable to maintain low electrical contact resistance and to make the strength of electric field throughout the material bed as uniform and large as possible in the dewatering process. As it is difficult to estimate local strength of electric field acting effectively for dewatering in the material, the average strength of electric field, E av , applied to all over the bed in the dewatering process is discussed as follows.
If L and λ av are assumed to be nearly constant, V and I should be increased to intensify Eav. L is actually decreased and λ av is also usually decreased with dewatering, as described above.
Incidentally, EOD can be operated under constant voltage or constant current condition. Accordingly, when an electric field is applied at a constant voltage operation (V \(\,=\,\)constant), E av in Equation (16) should be increased theoretically because of the decrease of L. However, a net value of E av applied to the material being dewatered is just reduced due to the occurrence of a large electrical contact resistance enhanced with the progress of dewatering. While in the operation at constant current (i \(\,=\,\)constant), net E av in Equation (16) could be increased with decreasing λ av in spite of the enhancement of electrical contact resistance. In this operation, however, the electric power would be poorly utilized; in other words, the applied voltage required to maintain a constant current condition would be too high due to the large electrical contact resistance. Equation (16) also indicates that E av is increased if A is smaller.
From the viewpoints mentioned above, various applications for better and higher performance of EOD can be devised in principle to improve the dewatering rate, the final water content, and the efficiency of electric power consumption for water removal.
2.3 Characteristics of Materials Suitable for EOD
where ζ is the zeta potential of the solid particle and D is the dielectric constant of liquid. E, μ, I, and λ are as before. The electro-osmotic flow is a phenomenon that is caused by the ζ-potential in an electric double layer at the interface between different phases. In the derivation of Equation (17), it is assumed that the thickness of the electric double layer is quite small compared with the diameter of the capillary or pore size. As the electric double layer thickness is usually smaller than the capillary diameter, Equation (17) is applicable to most cases, and u is independent of the capillary structure; in other words, the electro-osmotic flow is not affected by the diameter of the particles contained in the dewatered material. Hence, EOD can be particularly effective for the material including very fine particles (e.g., colloids).
Equation (17) also indicates that u is proportional to the electrical properties such as the ζ-potential of solid particles and the dielectric constant of liquid D, and that is inversely proportional to the viscosity μ and the specific electric conductivity λ of the liquid. Therefore, large ζ and small μ and λ of the original material can be appropriate for EOD, and it is advantageous that ζ changes to the larger and λ changes to the smaller value in the dewatering process.
As the electro-osmotic flow is theoretically considered to be independent of the capillary structure, EOD could be effective for materials that have minute capillary structures like fibrous plants.
Sewage sludge or activated sludge can hardly be dewatered mechanically, because such sludge disposed biologically contains very fine particles such as microorganisms and organic decomposed products.
The suspended particles in typical sewage sludge generally have negative ζ-potential. However, in the case that many kinds of colloidal particles are contained not as the suspended particles in the liquid, the viscosity μ of the liquid becomes high, resulting in a disadvantage for EOD.
Coagulated or agglomerated sludge produced in wastewater and sewage treatments is very compressible, collapsible and transformable, so that such a sludge is extremely difficult to dewater by mechanical methods such as vacuum dewatering, pressure dewatering or expression.
Gelatinous materials are often found in food processing products, and those are also hardly removed by mechanical dewatering methods.
Proteins, polymers made of amino acids, exist as both cationic and anionic electrolytes in aqueous solution and have a net charged surface with positive or negative ions environmentally depending on pH of the solution. Then the proteinaceous macromolecules have positive or negative ζ-potential in the solution, and the proteins may be regarded as the particulates in solid-liquid separation for bio-materials.
If corrosion of the electrode material is caused by electrolysis, the bio-materials dewatered electro-osmotically are contaminated, and also they may be denatured by ohmic heating.
3 Applications of Electric Field for High-Performance EOD
As shown in Fig. 5, EOD under the condition of DC power supply is successively performed downwards and the water content is reduced considerably in the upper part of the bed opposite to the drainage surface. The reduction of the water content near the upper electrode enhances the increase of electrical contact resistance between the upper electrode and the top surface of the sludge bed shown in Fig. 4, resulting in a large expenditure of the voltage applied to the bed. In such circumstances, the applied electric field does not act effectively in the lower part of the bed, and then continuation of EOD becomes increasingly difficult.
Different applications of electric field, besides continuous DC, have recently been investigated in an effort to improve the performance of EOD. New developments for high-performance EOD are described in the next section.
3.1 Electric Field Application with Electrode Polarity Reversals
An improvement for the performance of EOD under continuous DC condition had been originally tested by Gray and Somogyi (1977). They investigated an electro-osmotic treatment with the electrode polarity reversals of every 30 min for red mud sludge and suggested that reversals of electrode polarity or electric current direction improved consolidation of the sludge and more efficient dewatering.
The electric field application of alternating current (AC) with periodic reversals of the electrode polarity has been also investigated from the viewpoint of lowering an increase of the electrical contact resistance between the upper electrode and the sludge being processed (Yoshida et al. 1999). By applying a very-low-frequency AC electric field combined with mechanical expression to the sludge bed, the direction of liquid flow in the bed by electro-osmosis can be reversed periodically with time, and this EOD process was expected to be useful for sludge dewatering from both sides of the bed between the electrodes.
3.2 Interrupted or Intermittent Electric Field Application
Lockhart (1986), Lockhart and Hart (1988) studied many of the variables in terms of EOD, and one of the variables was interrupted electric power application; in other words, on–off power application. According to their studies, the experimental results of on–off alternations with equal periods up to 5 min suggested that better results than continuous DC power application were not always appeared, and that the results depended on the material dewatered and the apparatus used in the experiments. It was also noted that the interrupted power applications did not offer any inherent advantage or power saving capability, but the on–off power regimes were not suggested to be not useful for practical value from power interruptions.
In the rectified half-wave IEF, a diode was added to the AC circuit described before for half-wave rectification of AC, and on-time of the electric power supply was equal to off-time, and the on-off time was set in the region of more than 50 s, namely, very low frequency below 0.01 Hz of AC. Then the process of EOD under the IEF was investigated experimentally, under both conditions of the same PV and the same EV as the constant voltage applied under DC or AC condition (Yoshida 2000).
The effect of the half-wave IEF under pulsed DC was investigated by using a cross-flow continuous-type experimental apparatus which consisted of two vertical cylindrical electrodes. In such an apparatus used for electrokinetic dewatering of slurry, an electric field was applied to the slurry flowing downwards continuously between the vertical cylindrical electrodes. Thus the slurry can be dewatered electro-osmotically toward both sides of the flowing path across the vertical electrodes. The half-wave IEF was also available for the cross-flow continuous dewatering apparatus, and the intermittent power application could be useful for improving the performance of EOD not only in the batch experiment but also in the continuous one (Yoshida 2001).
3.3 Electric Field Generated by Combination of Constant Current and Constant Voltage Conditions
The process of EOD has been principally operated and investigated under conditions of either constant voltage, abbreviated to CV, or constant current, abbreviated to CC here. If the electric resistance between two electrodes R E , namely the electric resistance of the dewatered material is increased with proceeding of the dewatering, the EOD process operated at CV goes to an end because the electric current passing through the material bed gradually decreases, while the operation at CC has to be stopped forcibly because the voltage required to maintain the condition of CC is too high. The increase or decrease of R E depends on the physical and electrical properties of the material to be dewatered. Therefore, a combination of CV and CC could be determined according to the properties of the material so as to make the average strength of electric field, E av , applied to the whole bed of the material as large as possible in the dewatering process, as described previously in the Section 2.2.
3.4 Electrode Arrangements and Configurations
Electrode arrangements for electrodewatering in relation to impoundments had been investigated by a group of the Commonwealth Scientific and Research Organization (CSIRO, Australia) (Lockhart 1986). Both horizontal and vertical electrode arrangements were examined for in situ dewatering of sand and coal washery tailings, and their electrodes were respectively set with mesh arrangement with considerable open area in each impoundment. The field trials for dewatering were carried out using horizontal electrode arrangements at a coal washery tailing pond, and the findings were attractive, especially considering the high cost of chemical flocculants needed for centrifugal dewatering practice. The vertical electrode arrangements were found to be more appropriate at a sand washery tailing pond.
From this point of view, electric field application was experimentally investigated by decreasing the area of the plate-type upper electrode opposite to the drainage surface compared with the cross-sectional area of the sludge bed, and the influence of such electric field application as decreasing the area of the upper electrode on the dewatering process was discussed in terms of total amount of water removed and electric power consumption (Yoshida and Okada 2006).
4 EOD of Bio-Materials
As described earlier in the Section 2.3, EOD has the potential for dewatering of biomaterials and has some advantages compared with conventional mechanical dewatering methods. It has so far been used in practice mainly for dewatering of biomaterials or biosludges produced from bioindustry and the related industrial fields: for example, sewage/activated sludge, waterworks sludge, food processing products and wastes, and biomass sludge.
4.1 Sewage/Activated Sludge and Biomass Sludge
Many installations for disposal of biosludge produced by wastewater treatment process are used widely, so that a large amount of excess sewage/activated sludge gets discharged from the process. Such sludges that are colloidal in nature with extremely small particle size are very difficult to dewater purely mechanically.
CSIRO in Australia investigated the applicability of EOD to aerobic wastewater treatment sludges which were particularly difficult to dewater using conventional mechanical equipment (Barton et al. 1999). It was reported that the bench-scale dewatering experiments produced cakes with solid contents of 42–46% in weight using EOD, compared with 24–30 wt% using pressure dewatering alone. Thus, EOD showed a substantial increase in the cake solid contents from sewage sludges produced by biological wastewater treatment processes. Barton et al. (1999) discussed a mathematical model for EOD described in the Section 2.1; the basic differential Equation (6), which represents the process of EOD, for the adaptability of application to sewage treatment sludges, and consequently preliminary results provided meaningfully a reasonable simulation of the modeling procedure for the EOD process of sewage sludges as well.
In order to identify a relationship between water removal limits by EOD and the forms of water in sewage sludge, the freezing–thawing technique was also examined using an analysis of proton nuclear resonance (NMR) spectroscopy. And the NMR analysis showed to provide a good way of quantifying the degree of association of water with the solids in thickened sewage sludge, and the dewatering limits by EOD was identified by estimating the forms of water removed by mechanical dewatering (Barton et al. 1999).
For the activated sewage sludge in wastewater treatment, the combined field techniques of both EOD and pressure filtration or expression have been investigated on laboratory and pilot-plant scales by many researchers to find the dewaterability of the sludge and the technical possibility for it. And these techniques were confirmed to be promising for the dewatering of the biological sludges in terms of attainable solid contents (to more than 60 wt%) and very low power consumption compared to that needed by thermal drying techniques (Smollen and Kafaar 1994; Saveyn et al. 2001, 2005, 2006).
Biomass sludge resulting from the concentration of waste slurry from biological wastewater treatment and enzyme production are rich in nutrients, and the sludge can be used as fertilizer for agricultural soils. For the purpose of this utilization, it has to be dewatered previously from around 3–5 wt% to 30 wt% in dry solid contents, which could be easily demonstrated by the operation of EOD experimentally, and low power consumption could be obtained when keeping the strength of electric field to a low level, since the electrical conductivity was quite high for the biomass sludge (Hansen et al. 2003).
4.2 Food Processing Products and Wastes
The operation of EOD combined with mechanical pressure (expression), which was called the combined field dewatering, has so far been applied to food processing industry, and several studies have been carried out on EOD of food materials.
To produce sardine powder for a gelatinous product such as “kamaboko", a continuous screw-press-type bench scale dewatering machine that is applicable to avoide protein denaturation of fish meat was developed by applying combined field of electro-osmotic and mechanical methods. In this EOD machine, the screw is used as one electrode and the strainer as the other electrode. Final water content of sardine minced meat soaked with water was only 60% by the conventional mechanical method, but it was reduced to less than 40% in only 15–18 min by applying the combined field (Suzuki et al. 1990).
The process of the combined field dewatering, involving electro-osmosis and expression, was studied experimentally for seaweed (Lightfoot and Raghavan 1994, 1995). They observed that the addition of electro-osmosis to expression significantly improved the performance of dewatering of seaweed. They also found that electro-osmosis reduces the energy consumed for producing kelp meal for animal consumption if dewatering is followed by thermal drying to produce the final product dried.
The potential benefits of combined field dewatering were also investigated for brewer's grain, apple pomace, and vegetable waste (Orsat et al. 1996). They conducted that their solid concentrations with the addition of an electric field to expression can be increased respectively from 30% to 48% for brewer's spent grain, from 23% to 53% for apple pomace, and from 11% to 67% for vegetable waste. As mentioned above, the combined field dewatering of kelp (seaweed) before drying process had been shown to be useful for reducing energy requirements for drying (Lightfoot and Raghavan 1994). This preliminary investigation led to the development of a pilot-scale operation for the production of kelp meal, and the kelp after treating chemically and draining was dewatered experimentally using the pilot-scale roller-press-type machine for the combined field dewatering (Orsat et al. 1999). The roller press consisted of seven rollers (four bottoms and three tops) and two idler rollers mounted on an aluminum truss frame, and the material to be dewatered was loaded onto a belt, which carried the material through the press rollers where the combined field was applied simultaneously. In this pilot-scale electro-osmotic roller press operation for kelp meal production, it was ensured that the combined field was effective at removing water from the drained kelp, in spite of remaining problems with capacity and reliability.
Vegetable wastes produced from the food industry are costly to handle because of their high moisture content. Effectiveness of the combined field dewatering for such vegetable waste sludges was studied experimentally on small scale (Chen et al. 1996). Chen et al. (1996) used fresh vegetable sludge samples made from one part by weight of cauliflower and two parts of cucumber as a model of vegetable waste. In the experiments with such a vegetable sludge, the final average water removal of 55% was achieved by the combined field dewatering, and this was twice as high as that of mechanical pressure alone and four times as high as that of EOD alone.
“Tofu" is a soy food generally regarded as one of the healthy foods and is very popular in east Asia. The production of tofu yields enormous waste stream known as “okara," which is the solid residue after separation of soymilk produced by squeezing or centrifugation of soybean mash. A large amount of okara discharged in tofu manufacturing process has to be dried and burned or sent to landfill, but the storage and transportation of it are very difficult because of its high moisture content on wet basis (around 80%). Hence, okara treatment and disposal have been a serious problem in food processing. To enhance the dewatering efficiency of okara, a twinscrew-press-type ceramic filter with electro-osmosis was designed and examined (Isobe et al. 1996; Li et al. 1999). It was reported that the water content of okara was decreased by the screw press from 85% to 74% of which the dewatering efficiency was 50%, and that was reduced considerably up to 40% in case of a batch compression process with the addition of electro-osmosis. The experiments by electro-osmosis were performed using DC and AC electric fields with the frequency from 0.2 to 0.5 Hz, and the low-frequency AC fields combined with mechanical pressure had the potential to be used in the dewatering of okara compared with DC operation (Isobe et al. 1996).
Removal of water by EOD from tomato paste suspension was also used to concentrate the suspension (Al-Asheh et al. 2004; Jumah et al. 2005). For the purpose of this treatmet, an apparatus was designed in a vertical orientation, and laboratory tests demonstrated applying electric field under both DC and AC operations to the tomato paste suspension held between two electrodes. The effects of applied voltage, electric current, height of the bed, pH, and initial solid concentration of the suspension were examined in terms of water removal and energy consumption for dewatering. It is reported that significant amounts of water can be removed by EOD under the operating conditions used. This process saved 70% of energy compared with that needed to dry the same amount of water. The application of AC electric field provided more promising results than those by DC application.
4.3 Miscellaneous Topics
There are a few interesting papers which are related to EOD applications where dewatering per se is not objective (Vijh 1999a,b,c; 2004). Electrochemical treatment of cancerous tumors has been studied experimentally. Vijh (1999c) proposed a theoretical model to analyze the primary mechanism of electrochemical treatment of the tumors. The idea for the analysis was that the process of electrochemical treatment can be regarded as a case of EOD of the tumor tissue with the consequent changes in pH, with the concomitant role of reactions at the electrodes. That is, the electrochemical treatment of tumor causes a net flow of water from the anode to the cathode, causing EOD of the tissue, based on the electrically induced flow of water trapped between the tumor cells. All the main experimental observations—for example, water removal near the anode and water accumulation near the cathode as well as the associated pH changes and other factors considered to be involved in necrosis—were explained by the analysis proposed. Some suggestions were made based on the analysis to explain the enhancement of the efficacy of the process of electrochemical treatment of cancerous tumors.
Electrokinetic remediation of contaminated soils and dredged sediments isanother application of EOD, which has attracted major attention. However, this subject is outside of the scope of this chapter (e.g., Shaplro and Probstein 1993; Reddy et al. 2005).
5 Closing Remarks
Although EOD has been examined both theoretically and experimentally for decades and its advantages in dewatering are well documented, commercial applications are still few. Typically EOD is not as cost-effective as a stand-alone operation. It is necessary to use it in combination with pressure or vacuum dewatering. Thus the equipment capital cost is higher than that of conventional dewatering equipment. Future R&D will hopefully allow cost-effective development of EOD-enhanced equipment for sludge dewatering and contaminated soil remediation.
- Gray, D. H. and Somogyi, F. (1977) Electro-osmotic dewatering with polarity reversals. Journal of Geotechnical Engineering Division. 103(1), 51–54.Google Scholar
- Gopalakrishnan, S., Mujumdar, A. S., Weber, M. E. and Pirkonen, P. M. (1996b) Electro-kinetically enhanced vacuum dewatering of mineral slurries. Filtration & Separation. Nov/Dec, 33, 929–932.Google Scholar
- Isobe, S., Uemura, K. and Noguchi, A. (1996) Dewatering of soybean residue “okara" by electro-osmosis and screw press, Proceedings of The Second International Soybean Processing and Utilization Conference. Bangkok, Thailand, pp. 523–527.Google Scholar
- Kondoh, S. and Hiraoka, M. (1990) Commercialization of pressurized electro-osmotic dehydrator (PED). Water Science and Technology. 22(12), 259–268.Google Scholar
- Li, L., Li, X., Uemura, K. and Tatsumi, E. (1999) Electro-osmotic dewatering of okara in different electric fields. Proceedings of The 99-th International Conference on Agricultural Engineering. Beijing, China, pp. IV58–IV63.Google Scholar
- Li, X., Nanayama, K, Uemura, K, Sakabe, H. and Isobe, S. (2002) Production of tofu sheet by electro-osmosis combined with mechanical compression. Proceedings of The Third Annual Meeting of The Society of Food Engineers, Japan. Tokyo, Japan. OF-5, p. 75.Google Scholar
- Lightfoot, D. G. and Raghavan, G. S. V. (1994) Combined fields dewatering of seaweed (nereocystis luetkeana). Transactions of the ASAE. 37(3), 899–906.Google Scholar
- Lightfoot, D. G. and Raghavan, G. S. V. (1995) Combined fields dewatering of seaweed with a roller press. Applied Engineering in Agriculture. 11(2), 291–295.Google Scholar
- Lockhart, N. C. (1986) Electro-dewatering of fine suspensions. In: H. S. Muralidhara (Ed.), Advances in solid-liquid separation. Battelle Press, Columbus, pp. 241–274.Google Scholar
- Orsat, V., Raghavan, G. S. V. and Norris, E. R. (1996) Food processing waste dewatered by electro-osmosis. Canadian Agricultural Engineering 38(1), 1–5.Google Scholar
- Rampacek, C. (1966) Electro-osmotic and electro-phoretic dewatering as applied to solid-liquid separation. In: J. B. Poole and D. Doyle (Eds.), Solid-liquid separation-a review and a bibliography-. Her Majesty's Stationery Office. London, pp. 100–108.Google Scholar
- Saveyn, H., Huybregts, L. and Van der Meeren, P. (2001) Enhanced sludge dewatering by electro-filtration; a feasibility study. Meded Rijksuniv Gent Fak Landbouwkd Toegep Biol Wet. 66(3a), 71–78.Google Scholar
- Shirato, M., Murase, T., Kato, H. and Fukaya, S. (1967) Studies on expression of slurries under constant pressure. Kagaku Kogaku. 31(11), 1125–1131.Google Scholar
- Smollen, M. and Kafaar, A. (1994) Electro-osmotically enhanced sludge dewatering; pilot-plant study. Water Science and Technology. 30(8), 159–168.Google Scholar
- Suzuki, Y., Konno, M., Sato, Y. and Shishido, I. (1990) Development of continuous dehydrator for fish meat by electro-osmotic method. Kagaku Kogaku Ronbunshu. 16 (6), 1133–1137.Google Scholar
- Vijh, A. K. (1999c) Electrochemical treatment of tumors (ECT): Electro-osmotic dewatering (EOD) as the primary mechanism. Drying Technology. 17(3), 585–596.Google Scholar
- Wakeman, R. J. and Tarleton, E. S.(1999) Filtration -equipment selection modelling and process simulation. Elsevier Advanced Technology. Oxford, pp. 244–246.Google Scholar
- Yamada, K., Hobo, Y., Hayashi, N., Uchida, E. and Watanabe, S. (2001) Achieving increased efficiency in a solid-liquid separation process using electro-osmosis. Proceedings of Filtration and Separation Symposium '01. Tokyo, Japan, pp. 161–164.Google Scholar
- Yamaguchi, M., Arai, T. and Matsusita, H. (1986) Dewatering of Wastewater and sewage sludges by an electro-osmotic dewatering system. Yosui To Haisui (Water and Waste). 28(4), 36–41.Google Scholar
- Yoshida, H., Tanaka, K. and Komatsu, M. (2001) Influence of on and off times of power application on electro-osmotic dewatering under intermittent electric field. The Transactions of Filtration Society. 2(1), 27–32.Google Scholar
- Yoshida, H. and Yukawa, H. (1991) Analysis of dewatering processes enhanced by electro-osmosis. Fluid/Particle Separation Journal. 4(1), 1–7.Google Scholar
- Yoshida, H. and Yukawa, H. (1992) Analysis of electro-osmotically enhanced sludge dewatering. In: A. S. Mujumdar (Ed.), Advances in drying, vol.5. Hemisphere, Bristol, pp. 301–323.Google Scholar
- Yukawa, H., Hakoda, M., Okonogi, H. and Yoshida, H. (1986) Electro-osmotic dewatering of wasted activated sludge. Yosui To Haisui (Water and Waste). 28(6), 30–35.Google Scholar