If a solid and a liquid are separated from a suspension, this is possible with a belt filter press, a dewatering table (or thickening table, belt thickener), a chamber filter press (or plate filter press) or a decanter. The result is filtered liquid and a solid mass of solids. Examples of suspensions are water treatment sludge, manure, digestate or dredging. Below we explain the operation of a belt filter press, a dewatering table and a chamber filter press.
Example of an belt filter press
(Sludge) dewatering with a belt filter press
A sieve belt press is a machine that compresses a suspension between filter cloth (filter belts), whereby pressure can be built up with the aid of rollers, which results in separation of a solid and a liquid. A belt filter press is part of a larger installation. In such an installation you will find all sorts of peripheral equipment, such as a polymer installation, pumps (sludge supply, belt rinse water, filtrate discharge) and a cake discharge installation.
Applications for filter belt presses can be found in the dewatering of sludge and slurry in waste water treatment, soil cleaning, mining industry, chemical industry, agriculture and horticulture, etc. In addition, belt presses are also used in fruit processing (preparation of fruit juices and wine making). In contrast to a (chamber) filter press, a sieve belt press is in continuous operation.
Sludge removal is an important operational cost item for water treatment. The lower the dry matter content of sludge, the more is paid for the removal of water. The dry matter content in organic waste water sludge rises to around 25%; 60 percent is certainly possible for some inorganic sludges.
Advantages of a belt filter press
- Robust and continuous process
- Autonomous machine; works without operator intervention (system cleans itself)
- Large pre-drainage and press zone
- Maximum dewatering through cracking in the sludge cake while passing the rollers
- Maximum number of rollers in a relatively compact installation (7-15 pieces for extra high dry matter content)
- Maintenance friendly
Example of a (pre)dewatering table or belt thickener
(Pre)dewatering with a dewatering table
A belt filter press is often preceded by a (pre) dewatering table, thickening table or belt thickener. This is also referred to as a gravity drying step, whereby a large amount of free water can be separated from the sludge water mixture. A dewatering table increases the separation efficiency of the filtration at a low cost. On biological sludge, separation yields of more than 99 percent and dry matter concentrations above 10 percent are certainly possible.
Advantages of a dewatering table
- Relatively cheap
- Energy efficient
- Separation efficiency of more than 99 percent for biological sludge
- Works completely autonomously
- Maintenance friendly
After this step, the sludge is mixed with a flocculant or floculant, resulting in a conditioned sludge. A dewatering table is a simplified version of a belt filter press.
Voorbeeld van een kamerfilterpers
(Sludge)dewatering with a chamber filter press
From a technical point of view, a chamber filter press or filter press is a relatively simple and very flexible press installation that is suitable for many applications, particularly in the food industry and mining. The medium to be filtered is pressed batchwise through vertically hanging plates with filter chambers. There is a filter cloth on each plate. This type of press achieves the highest separation efficiency of all mechanical separation techniques, because the product can be pressed directly into sealed ” chambers ”. A chamber filter press achieves a solid content in the filter cake of 30 to about 70 percent depending on the suspension and dewatering properties.
Advantages of a chamber filter press:
- maximum separation efficiency: dry cake, pure liquid
- robust technology with long service life
- a mechanical separation technique in which both cake filtration and cake drying can go together
- everything that comes into contact with the product to be filtered can be made in (resistant) plastic