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Both in the preliminary and final setting basins the sludge should be separated.
To a large extent, the sludge resulting from the final clarification is returned to the circuit. A small part of it (so-called "excess sludge”) is fed to the dewaterting process, like primary sludge.
This can begin in a pre-thickening basin, in which the pre-sludge and excess sludge are mixed and thickened (drained) by the gravitational force.
For this purpose, rakes are usually used. The further dewatering process is usually carried out by machine technologies.
For this purpose, we offer:
- Belt thickeners
- Belt filter presses
The DEWA BTN belt thickener is an outstanding item of equipment for thickening the excess sludge at municial plants. It belongs to the generation of automatic sludge thickeners with the highest sludge concentration when discharging at very high throughput and very low polymer consumption.
Retaining rates of 95-98% speak for themselves. The same applies to the corrosion resistance and top level quality of the materials and components used in the system. Manufactured in six sizes, the BTN belt thickener is a robust, reliable and economical solution.
Belt Filter Presses
For dewatering of sewage sludge, we offer our robust DEWA belt filter presses. Depending on the TS content of the lightweight sludge, the aforementioned belt thickener can be incorporated into existing presses. This is a good arrangement to save space. The machines are characterized by high efficiency, compact design and low maintenance requirements. Water-saving operation ensured by use of the filtrate is a matter of course.
The DEWA screw conveyor horizontally or vertically transports dewatered industrial and municipal sludge, grit or other technical materials. Due its closed design, odour and dust are avoided. The shaftless screw conveyor (auger flight) prevents sticking or trapping the conveyed materials to the shaft and increases the handling capacity.
The customer can select various materials. The replaceable wear plates are made of UHMW-PE. The bolted cover allows easy maintenance of the operated system.
Our automatic polymer preparation station AP from DEWA® is intended for generating flocculation aid solutions. The batched solution is then stirred into the sludge to be dewatered before the sludge comes into the filter press. This poly-electrolyte solution is required for flocculation of the sewage sludge. The like-charged groups on the polymer chain create interacting repulsive forces. Due to these forces, the solid particles of the sludge dissolved in the water are bound to chains (flakes).
Without this flocculation of the sludge, no subsequent dewatering in the filter press would be possible because the solid particles are so small that filter fabric cannot separate them from the water.