HYDRAULICS OF UPFLOW FILTERS

Abstract

Separation of impurities from water when it passes through a sand bed, is found to be due to a combi-nation of several individual processes. A good deal of research has been made to assess the contribution of each of these processes and various theories have been put forward to explain the mechanism of filtration. The design of sand filter has developed with the development of the theory of filtration. The introduction of upflow filters is a recent development and it shows a lot of promise. Upflow filters have been in use on a large scale in Russia for over a decade. There is, however, a lot of scope for research in the theory of upflow filtration and improve-ment in the design of upflow filters. This dissertation is the result of a study of the available literature & some experimental work done by the author on the hydraulics and design of Upflow Filters. The experimental work was carried out with the help of a 10 cm square cross-section filter model. Test runs of the filter model were carried out first at the Roorkee University laboratories and then at the public waterworks at Lucknow where the filter model was run in parallel with the commercial rapid gravity filters of the waterworks for a direct comparision of performance. It has been found that for the same rate of filtration an upflow filter has a longer run and a lesser final head-loss than a conventional downflow rapid filter. An upflow filter can also cope with water of a higher turbidity than a downflow filter on account of the coarse media also taking part in the filtration process. In this study a new idea of reducing the cross-section of the filter where the coarser media are located, has been introduced and tried. This improves backwashing of the coarse media and the process of flocculation in the lower portion of the filter. This arrangement would also reduce the cost of the filter appreciably due to reduction in the quantities of the filter media and the under-drainage system of the filter. • • •