Dewatering
In full scale trials, electrokinetic geosynthetic (EKG) materials retrofitted to belt filter presses have increased the solids contents of sewage cake from ~20% dry solids to ~31% dry solids and diamond mine tailings from ~62% dry solids to ~75 dry solids%.
The former resulted in a 40% volume reduction and prospective cost savings to water companies of £132,000 per belt filter press machine per annum.
The latter offered the possibility of substantial cost savings to mining companies associated with tailings disposal and management.
Details of these trials are available on the case studies page.
EKG materials have applications in ground dewatering including:
- Electrokinetic belt filter press
- Electrokinetic plate filter press
- EKG dewatering bags for mixed wastes
- In situ dewatering of lagoon wastes
Dewatering of materials using filtration or centrifugation becomes increasingly difficult as the materials become progressively more fine grained. Electroosmosis can aid the dewatering process and is particularly suited to fine grained materials. The benefits of this are particularly evident in materials such as clays, sludges and fine tailings, see graph below.
Electrokinetic Belt Filter Press
Electrokinetic belt filter press technology has been developed by Electrokinetic Ltd. The basic set up is shown below.
The fundamental concept of the system is to add the electrokinetic effects whilst preserving, the existing hydraulic dewatering performance.
The system operates by confining the voltage to and controlling the voltage within the dewatering zone. It is designed to be adaptable to a wide range of existing conventional belt filter presses.The benefits of the electrokinetic belt filter press over alternative dewatering methods include:
- Increased solids content of dewatered cake, e.g. raising dewatered sewage cake from 20% dry solids to over 30% dry solids
- Improved stackability of dewatered cake
- Reduced overall energy consumption
Refer to the case studies page for more details.
EKG belts are available in a variety of designs to optimise the dewatering of different types of slurries and sludges.
The electrokinetic belt filter presses are now commercially available either as new equipment or as retrofits to installed machines. In order to adapt a machine the conversion requires:
- New belts
- DC power supply
- Brackets brushes and cabling
Electrokinetic Plate Filter Press
The understanding gained from the development of the EKG materials for the electrokinetic belt filter press is being applied to the development of an electrokinetic plate filter press.
The overall concept is the same as for the electrokinetic belt filter press: the addition of electrokinetic function together with complete preservation of hydraulic function to yield improved performance.
Similarly to belt filter presses fitted with EKG belts and ancillaries, the concept for the EKG plate filter press has been to develop a system which can be retro-fitted to a wide variety of existing machines.
Trials so far have used machines with plate sizes of 300mm and cake thicknesses of 30 – 50mm. Results show that the technology has improved the dewatering performance of problematic sewage containing 70% surplus activated sludge (SAS) from ~20% to 35%. Data (see below) collected during the trial runs show clearly the effect of electrokinetic dewatering after the squeeze stage.
Final cake solids EKG Control
70% SAS : 30% primary 37.0%ds 20.4%ds
40% SAS : 60% primary 45.9%dsd 32.1%ds
Control cake 20% dry solids EKG cake 37% dry solids
Clean filtrate water
EKG Dewatering Bags
Belt presses and plate presses are suited to materials of a homogeneous nature, and constant supply. Also owing to the capital cost of the equipment, they are generally used where the volumes of waste to be treated are large. Such applications are to be found in water and sewage treatment, mining and large scale industrial processes.
However there are some market sectors whose waste production is characterised by difficult to dewater heterogeneous materials, in intermittent supply and often in small or medium sized volumes. Example sectors include, ground engineering & drilling, gully clearance, small scale dredging, agriculture and some parts of the food industry.
Matrix of waste dewatering showing applications of EKG
EKG dewatering bags have been developed to offer a simple, low cost dewatering method.
A small scale example of the dewatering performance is shown below.
In Situ Dewatering of Lagoon Wastes
As shown above, some wastes are stored in temporary lagoons for subsequent processing. If the material is thicker than the above (top left photograph) then it may fall into the class, which can be described as ‘too thick to pump – too thin to shovel’. Further if the lagoon is historic in nature then it may contain significant heterogeneities such that an in situ dewatering treatment is the appropriate method.
EKG materials in the form of electrokinetic prefabricated vertical drains or ePVDs can be used to dewater lagoon wastes in situ. An example is given on the case studies page.
