Electrical field: A historical review of its application and contributions in wastewater sludge dewatering

The production of wastewater treatment sludge, the basic characteristics of the sludge and the state of the water in the sludge are described in this paper. The methods for the determination of bound water content are discussed. The literature (including patents) on sludge dewatering and drying is reviewed, including vacuum filters, belt presses, centrifuges, direct dryers, indirect dryers and combined mode drying systems. The issues related to drying are briefly discussed. Photographs or schematics of typical dewatering and drying systems are also included.

Sludge dewatering and drying

Influence of salt, pH and polyelectrolyte on the pressure electro-dewatering of sewage sludge

The efficiency of separation processes can usually be assured either by an energy input or by external forces. The majority of conventional sep- arations applies mechanical or thermal energy in combination with pressure or gravity forces. The ability of superimposed electric fields to improve separation processes has been well known for many years. The familiar industrial applications range from solid-solid separation in the beneficiation of ores in the mining industry, coalescence of “water-in-oil” emulsion in the petroleum industry, to cleaning of exhaust gases from solid particles in various technologies.

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Electric Field Driven Separations: Phenomena and Applications

Innovative technologies for producing and preserving intermediate moisture foods: A review.

The electroosmotic dewatering of a homogeneous semisolid material is investigated. The basic differential equation for electroosmosis through compressible materials is derived by use of Kobayashi’s equation, which considers the tortuosity of a flow path and the effect of the hydraulic pressure profile in the materials. It is recognized from Kobayashi’s equation that at the impermeable upper wall the electroosmotic flow and the pressure flow compensate each other. The relation among local hydraulic pressure, solid compressive pressure and external pressure is also derived, and is the same as those in mechanical filtration and expression. It is assumed in the analysis that no electroosmotic flow occurs in the layer where the local void ratio is smaller than a certain critical value. Based on numerical calculation, the pressure flow opposed to the net flow propagates from the upper electrode to the lower electrode. The electroosmotic dewatering rates of a homogeneous bentonite clay material calculated by the present method compare favorably with experimental observations.

Analysis of Electroosmotic Dewatering

To analyze the electroosmotic dewatering process precisely, the variations of water content and electric potential distributions in the sludge are made clear. The distributions of water content and electric potential in gelatinous bentonite sludge with electroosmotic dewatering were studied experimentally under the conditions of both constant voltage and constant electric current. It is proved that the water content distribution is generally related to the electric potential distribution throughout the dewatering process. Electroosmotic dewatering under constant voltage is compared with that under constant electric current. Electroosmotic dewatering combined with vacuum dewatering is also discussed from the viewpoint of these distributions.

Water content and electric potential distributions in gelatinous bentonite sludge with electroosmotic dewatering.

It is possible to apply electroosmosis to dewatering of sludge In this paper, the mechanism of electroosmotic dewatering of compressible sludge under condition of constant electric current was discussed, based on the model of electroosmotic flow through the particle packed bed, and the effects of the operating conditions on the rate of electroosmotic dewatering and the electric power consumption were theoretically analysed The equations obtained theoretically were confirmed experimentally under condition of constant electric current with the compressible sludges such as white clay, magnesium hydroxide and bentonite Theoretical equations were available for the design of electroosmotic dewatering apparatus The electroosmotic dewatering was particularly effective for gelatinous sludges

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Fundamental study on electroosmotic dewatering of sludge at constant electric current

Electroosmotic dewatering is very effective for sludge which is difficult to dewater by mechanical methods. Its use under condition of constant voltage was investigated. The mechanism of electroosmotic dewatering for compressible sludge under condition of constant voltage was studied by using the model of electroosmotic flow through a compressible-particle packed bed. The rate of electroosmotic dewatering and the electric power consumption were theoretically analysed. Experiments were performed by using compressible sludges such as white clay and bentonite. The equations obtained theoretically were confirmed experimentally. The theoretical equations of electroosmotic dewatering proposed in this paper are useful for the design of practical electroosmotic dewatering equipment. A few characteristics of electroosmotic dewatering under condition of constant voltage are also shown.

Hiroshi Yoshida

Papers

Analysis of Electroosmotic Dewatering

Water content and electric potential distributions in gelatinous bentonite sludge with electroosmotic dewatering.

Fundamental study on electroosmotic dewatering of sludge at constant electric current

Electroosmotic dewatering of sludge under condition of constant voltage.

Combined operation of electroosmotic dewatering and mechanical expression