EKG Dewatering and Stabilisation
Dewatering of slurries and sludges which is offered by Electrokinetic is a requirement of a large number of processes and activities. The science and engineering of this activity recognises four broad stages:
- sedimentation or settling: usually achieved by some manner of active or passive settling of solids through a liquid column.
- thickening: taking a liquid mixture such as a sludge and removing water to produce a higher density liquid or paste.
- dewatering: taking a sludge or paste and removing water to effectively create a phase transition wherein the material has been dewatered
- drying: cake (dewatered sludge) is dried to produce a friable granular or free flowing material.
Each stage of the process has a variety of methods that can be adopted. Removal of water from fine grained material is most challenging, as solid particles settle very slowly (sedimentation and thickening), or water flows very slowly through a matrix (dewatering). EKG electroosmosis combined with filtration can yield enhanced performance with increased solid content or increased speed in the dewatering process to the extent that filtration of challenging material can be viable. Aimed at mixtures of water and fine grained solids, there are multiple distinct applications for EKG dewatering methods. Some applications are outlined below.
EKG Dewatering Bags
- Combine electroosmosis and hydraulic filtration to permit dewatering in hanging bags – previously impractical or effectively impossible
- Enable removal of small volumes of water from industrial waste resulting from food production
- Enable removal of water from arisings from borehole drilling
- Enable removal of water from arisings from roadside gulley operations
EKG In Situ Dewatering
- Some materials are placed in open voids in the ground (owing to space availability and the difficulty in dewatering slurry)
- Where materials are very soft and fine grained, removal of water is challenging when material is too thin to shovel but too thick to pump
- Electrokinetic methods combine electroosmosis with conventional well-point technology to permit effective in situ water removal.
The operation of EKG dewatering bags requires the following ancillary equipment:
- a simple framework or a drainage platform
- slurry delivery method e.g. pumping
- a DC supply 0 to 60V up to 2kW per bag depending upon slurry characteristics
- electrical cables for connection
- an anode ring and one set of sacrificial rods.
HOW DEWATERING BAGS WORK
PERFORMANCE AND CAPACITY
The EKG dewatering process involves topping up of the content during removal of water, therefore the overall volume of material that can be removed in one process can range from 2m3 to over 10m3, depending on the solids content and the dewaterability of the waste material.
EKG dewatering bags will operate on a slurry of approximately 0.5% to 10% dry solids and will raise the solids content over a period of 1 to 3 days depending on operating voltage and slurry characteristics.
Typically, the final solids contents for an organic slurry is in the range of 15 to 35% and for a mineral slurry 30 to 50% plus. For multipurpose applications, EKG dewatering bags can be emptied by attaching lifting ropes to the two toe loops at the bottom of the bag and rotating and emptying the bag as shown below.
The anode comprises a circular mounting ring and a series of 16 mild steel rods. The rods can be up to 25mm in diameter and are gradually consumed, the rate of which will be dependent on the characteristics of the slurry.
EKG dewatering bags can be operated with or without the use of flocculent and or coagulant. The use of these chemical additives may enhance dewatering and reduce the time required to turn a slurry into a solid.
EKG In Situ Dewatering
- EKG materials formed as prefabricated vertical drains can increase the rate of consolidation through electroosmotic flow. This may be employed when dewatering materials for subsequent excavation or in situ ground improvement prior to site development.
- In fine grained soils, the electroosmosis induced flow rate can be 3-4 orders of magnitude greater than the hydraulic flow rate.
- Vertical drains can be inserted into the ground by lance or mandrill. Treatment reduces consolidation time by 50-80% compared to conventional wick drains and does not require the addition of surcharge.
- Typical application of in situ EKG dewatering is lagooned materials such as mine wastes or sewage sludges, materials that tend to have high water contents and low hydraulic conductivity.
EKG In Situ Dewatering Applications
- The technique is applicable in situations where conventional approaches are impractical or uneconomic (such as wick drains + surcharge, cementitious stabilisation, dilute and dewater).
- Each application requires individual consideration relating to target strength, speed of treatment and cost.
- Treatment can accommodate these objectives by varying the number of installed electrodes, the applied voltage and the duration of treatment.
- Examples of the use of this technique are the remediation of historical lagoons e.g. tailings or industrial treatment sludges. Please see our download page for examples of the use of this technique.