Tube settlers are gravity settlers wherein the settler is provided with No. of inclined tubes to increase the surface area of separation of solids from the liquid.
The basic theory of tube settlers is that it reduces the detention period to few minutes and achieves the required settling of the turbidity in comparison with conventional settling basin having detention period of 1-4 hrs. This is possible because of the vast area for settlement offered by the tubes installed within the clarifier unit. The area of settling basin is reduced with the high over flow rates viz. to the extent of two to three times higher than convention basins.
The flocculated water is fed into the feed basin centrally located in the gravity settler. The Tube settler is characteristically provided with steep bottom hoppers.
Heavy flocs will settle faster in the hopper of the tube settler while the light particles enter the inclined tubes. Due to a very low velocity of particles inside the tube and also due to the large surface area of the tube, the flocs agglomerates into the bigger size and slides down from the tubes into the hopper, this is then removed as sludge from the tube settlers.
As the units are provided with steep hoppers, there is no need to provide any sludge scrapping/ collection mechanism. Sludge blow off is affected by the static head of water in the tube settler. Sludge is withdrawn from the bottom of the Tube settlers as underflow and sent to sludge sump for the further de-watering process. The clarified water is obtained as an overflow from the tube settler is sent for further treatment in Sand Filters.
Tube settlers are designed based on specific overflow rates and the settling velocity of the solids.
Tube settlers are largely prevalent in large raw water treatment units and help in minimizing capital cost.
