| Filtration is the key step of a water-treatment process. Some specialists in the world put forward the theory of reverse grain filtration what would be of high filtration efficiency and good water quality comparing to Down-flow filtration. Up-flow filtration with coarse sand media, the water intaking from the bottom layer where the particle diameters of coarse media were the widest and outputting from the surface layer where the particle diameters of coarse media were the thinnest in the single media, was studied theoretically and experimentally in this research. It solved the difficult technical problem of reverse grain filtration. Pilot-scale experimental results showed that, comparing to conventional gravity filtration, the up-flow filtration has greater capacity in containing removed suspended solid and producing filtrate under the test conditions. Coarse media with particle diameter ranging 0.63-2.00mm were used in order to apply relatively higher backwash rate of 21 L/(m2 .s) for achieving better media clean-up after a filtration run. Under the test conditions, the media thickness ranging 82-85 iron, water temperature ranging 6-27, and influx turbidity of 30 NTU, it achieved the results of the average filtration rate ranging 16-18 m/h, the average effluent turbidity of 1 NTU, and action cycle ranging 14-24h. Further, full-scale experiments were carried out and the results demonstrated that the up-flow filtration with coarse media was efficient in removal of suspended solid, backwash of cleaning, and long action cycle. An effluent turbidity of 1 NTU was always achieved with an average filtration rate of 20 m/h. The design parameters of Liudong waterworks showed that, the rate of the Up-flow filtration improved over 50% comparing to the normal Down-flow filtration. So its filter area is less one-third than the others in same scale for less investment. It is a promise filtration technology especially suitable for the cases of filter renovation in order to increase its filtrate. |
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