Dewatering

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.

These include:

MaterialsTreatment

Method

Supply

  Constant Intermittent

 Large volume

Small volumeLarge volume

Small volume

 

Homogenous

Existing

Belt press

Plate press

Centrifuge

Small belt press

Pump and tanker

Temporary lagoon

Pump and tanker

  EK EKG belt press Small EKG EKG wick EKG

EKG plate filter press

belt press

Small EKG plate filter press

drains in temporary lagoon

dewateringbag

 

Mixed

Existing

Screen then thicken and centrifuge / belt or stabilise

Screen and thicken then tanker

Temporary lagoon thenscreen andtanker

Screen andthicken andtanker

  EKScreen thenEKG belt press

EKG dewatering bag

EKGdewateringtube

EKG dewateringbag

 

  EK methods actually applied by Electrokinetic

 

EKG belt filter press

Standard belt filter press technology with existing belt presses retro-fitted with EKG filter belts and electrical collection and distribution systems. Applications include:

(i) Mine tailings - dewatering of mine tailings in cases where dewatering was previously considered impractical or uneconomic. Dewatering of tailings to form cake permits the transportation by conveyor and the avoidance of disposal in tailings dams (tailings storage facilities).

(ii) Sewage sludge – dewatering of municipal sewage sludge to produce cake which is of a higher solids content than that achieved by pressure-driven filtration alone. This produces a reduction in the volume of waste and an improvement in its mechanical handling characteristics, both of which are economically beneficial.

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.

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 method.