Removing water from slurries and sludges is a requirement of a large number of processes and activities. The science and engineering of this activity recognises four broad stages:
1. Sedimentation or settling – usually achieved by some manner of active or passive settling of solids through a liquid column.
2. Thickening – taking a liquid mixture such as a sludge and removing water to produce a higher density liquid or paste.
3. Dewatering - taking a sludge or paste and removing water to effectively create a phase transition wherein the behaviour of the material which has been dewatered resembles that of a solid more than it does of a liquid. This material is often described as a ‘cake’. The transition between the phases is often indistinct.
4. Drying – cake (dewatered sludge) is dried to produce a friable granular or free flowing material.
With each stage there are a large variety of methods and approaches that can be adopted. Removal of water is most challenging from fine grained materials because the solid particles either settle very slowly through water (sedimentation and thickening), or water flows very slowly through a matrix of particles (dewatering). Electrokinetic has developed a wide range of EKG materials that combine electroosmosis and filtration in such a way as to yield an enhanced dewatering performance. This in turn offers improvements in performance (increase in solids content of dewatered material) or an increase in the speed of dewatering to the extent that filtration dewatering of some especially difficult materials becomes viable.
Understanding that electrokinetic dewatering is aimed at mixtures of water and fine grained solids, we have recognised several distinct applications for EKG dewatering methods.
EKG dewatering bags
Filtration bags which act to combine electroosmosis and hydraulic filtration to permit dewatering of materials in hanging bags – an approach which was previously impractical and in some instances effectively impossible. Applications include:
(i) dewatering of small volumes of industrial waste such as may be associated with food production.
(ii) dewatering the arisings of drilling boreholes e.g. for ground source heat boreholes.
(iii) dewatering arisings from roadside gully operations.
There are numerous other potential applications and Electrokinetic have recently invented and patented a new bag design which increases the speed, effectiveness and efficiency of the process.
EKG In situ dewatering
Some materials are placed in open voids in the ground (partly due to availability of the space and partly owing to the difficulty in dewatering the slurry). Where the materials are very soft and fine grained, dewatering is challenging because the materials are often in a condition, which may be described as “too thin to shovel but too thick to pump”. Alternatives to EKG treatment are to mix in dry solid material and stiffen the material in situ or to mix in water and pump to a subsequent dewatering plant (e.g. centrifuge or belt press).
Electrokinetic has devised a method
to combine electroosmosis with conventional well-point technology
to permit an effective in situ dewatering
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Electrokinetic is a trading name of Central Alliance Pre Construction Services Limited, Alliance House, Junction 41 Business Park, South Park Way, Wakefield, WF2 0XJ