Other sludge dewatering processes
Electro-dewatering (EDW) technology provides enhanced removal by non-mechanical means through the application of an electric field.
EDW of sludge removes water from the sludge through the principle of electro-osmosis. Electro-osmosis is an electrophoretic phenomenon, where movement of a solid relative to the surrounding liquid, or liquid within a porous solid, can take place on the basis of the charge at the solid−liquid interface when a direct electric field is applied.
An EDW device comprises a narrow horizontal channel through which the sludge is fed. A direct electric field is placed across the channel, with the anode at the top and the cathode and a filter cloth at the base. The cathode on which the filter cloth sits is porous to allow the water to pass through it.
The application of an electric field causes water to be extracted from the sludge under the influence of the electrophoretic force. No additional no mechanical force is required: the rate of water removal is dependent on the charge at the particle surface and the applied voltage.
A cake of up to 50% dry solids (DS) has been claimed from this method, with an accompanying sludge volume reduction of up to 75% at sludge loading rates of 75−150 kgDS/(m2.h) per m2 dewatering area.
Although the process appears to be very effective, the electrical energy consumption is significant – around 300 kWh per ton of water removed. This limits its application to sludges of relatively low water content, i.e. conventionally dewatered sludges. As such, it competes with thermal drying as a water removal technology, rather than mechanical dewatering technologies whose energy consumption is generally well below 20 kWh per ton water removed.
You can get a lot more information from ElodeUSA.com about this process. Some of the energy used per ton of water removed is incorrect here. It uses about 300w/kg of water removed. You can also learn about this process in more detail from this site. We have pilot tested over 50 municipal WWTP sludge cake and it was over 90% effective in reducing the cake for US plants to half the weight for 20%DS or lower cakes.
What's "300 W/kg" in energy per unit mass, Alex? Happy to correct the numbers (which were taken from Metcalfe and Eddy), but they have to be in the correct units :).
Sorry, that would be equal to 300kWh/metic ton of water removed or 300Wh/kg of water removed. We know this number is very close to this because we test almost every week with the machine you have pictured above.
Ok, so it's 300 instead of 100−150 kWh per ton of water removed - right? That means that the energy demand is higher than the figures given in Metcalf & Eddy.
Yes, the energy use is higher than stated of 100-150kWh/ton of water removed. But it is still far less than the low temperature dryer with heat pump which states that they use 250-300kWh/ton of water removed but our test showed about 650kWh/ton of water removed. That is why we offer our clients a free test in our machine to state what we can do. There are too many clients we see being burned by some people's data so we would like to provide more realistic data.
OK. We'll correct the figure on this page and see if we can find some credible thermal dryer SEC data from the literature
OK, the figure has been corrected to 300 kWh/ton