Solid-Liquid Separation
WEC Projects offers a variety of solid-liquid separation solutions designed to suit the client’s requirements, from low-cost, low-maintenance installations to sophisticated, high yield systems.
Solid-Liquid Separation Solutions
Sludge is a by-product of water and wastewater treatment, consisting of both a water and a solids component, with water making up the majority of the sludge (typically 85% to 98%).
The separation of the solids component from the liquid is important, particularly from the viewpoint of environmental responsibility. Both components need to be properly treated once separated to ensure that they meet the required standards with the water usually being recycled back into the system and the treated (dewatered) sludge being discharged safely into the environment.
Settling Systems - Thickeners
At its simplest level, a settling system operates by allowing the solids, which are heavier than water, to separate out and sink, or settle, to the bottom of a tank. This process is called thickening where the amount of water in the settled sludge is reduced. The sludge is then removed and, if necessary, processed further.
This process can be designed to operate on a continuous basis with sludge fed into the settling system continuously and, once it has settled and thickened, removed by a scraper for further processing (dewatering) or discharge.
Dewatering Systems
Dewatering describes the further removal of water from thickened sludge. Dewatering usually follows the settling process as it is more cost-effective to dewater sludge that has already been thickened.
Drying Bed
A drying bed is a simple method of dewatering sludge and usually consists of a concrete or brick enclosure with a porous bottom layer. The sludge is spread evenly across the bed where it undergoes a further settling process.
Once the sludge is settled, the water at the top layer of the bed is decanted while the remaining water drains through the porous bottom of the bed and the remaining sludge is left to dry in the sun. After two to four weeks, the solids, which have now formed into a “cake”, are manually or mechanically scraped off. Since the water has been removed from the sludge, its volume has been reduced, making it easier and more cost-effective to handle and dispose of.
Drying bed technology is usually deployed in remote areas where simpler, low-maintenance treatment solutions are required and are also ideal for smaller sewage and water treatment plants.
Filtration
The filtration of sludge involves forcing the water through the solids in order to separate the two.
Gravity filters
Gravity filters utilise filtration media such as woven geotextile Gravity allows the water to percolate through the filter medium while the remaining solids are trapped on the medium.
Pressure filters
A common pressure filter uses the force of pressure to push water through a filter medium such as a filter cloth. The dewatered solids cake remains behind on the filter cloth which is then removed periodically. There are many configurations of pressure cloth filters, the most common being a plate and frame filter press.
Belt filter
A belt filter utilises a revolving porous belt onto which the sludge is deposited. The water drains through the porous belt material while rollers press the remaining water out of the sludge (cake) which is then discharged.
Screw press
A screw press uses mechanical pressure to squeeze water from the sludge.
Centrifugal dewatering
Centrifugal dewatering is achieved through a mechanical device rotating at a relatively high speed. As the density of the solids in the sludge is higher than that of the water, the solids are forced to the outside of a revolving centrifuge vessel where they are continuously removed by a scraper.
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