Purification of process water in settling tanks
A Belgian company that is processing raw calcium carbonate into chalk powder for a.o. the plastics reworking industry and the paper and pulp industry had a problem with its waste and process water treatment unit.
The basic aim of this waste water treatment unit is to settle the removal of as many as possible undissolved particles from the wastewater. If the density of the particles is larger than that of water, they sink to the bottom (sedimentation). Sedimentation takes place in the wastewater settling tanks in which the waste water slowly flows. At the bottom of the basin of larger settling units often a sludge scraper is mounted to remove the sludge disposal. The steepness of the slope varies per type of settling unit. The steeper the bottom, the better the drainage to the middle. There are many sorts of settling tanks, round or rectangular, with or without sludge scraper or scum stripper.
All of the water that is used in the plant, for cleaning or in the process, is recuperated and fed to settling tanks. After the solid particles have settled and the water is therefore once again purified, it is pumped from the top of the tanks to the user reservoir.
The pump that was used on top of the tank used to be a vertical self priming centrifugal pump. This centrifugal pump is only suitable to pump water. But if there is a leak somewhere in the installation and sludge or calcium carbonate stone ends up on the floor and is then washed away – that very thick sludge will end up also in the settling tanks. The solid particles will most of the time than not settle quickly enough.
With the result that the pump on the tank has to pump back water for reuse that is still excessively contaminated.
Whenever pieces of thick sludge and calcium stone end up in this centrifugal pump, the pump will certainly stop and be damaged. Also tank overflow will occur.
The solution
In order to prevent the centrifugal pump running dry a density meter is installed in the feed pipe to the settling tanks. A Verderflex peristaltic hose pump is installed in a bypass line to emergency settling tanks that are located nearby.
The Verderflex hose pump is activated when the density meter measures excessive thick sludge. The waste water is then extracted and fed, via the bypass, to the emergency settling tanks were the Verderflex hose pump is installed. The peristaltic pump is deactivated again when the load level in the water returns to normal. The settling time in the emergency settling tanks is longer and the water is only pumped out once it is sufficiently clear. This means that the peristaltic hose pump VF 125 has solved a potential problem in the calcium carbonate plant.
If you have a pumping problem at your waste water treatment plant please contact us.
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