Flow Filtration Applications. On

Compared with conventionally rapid filter, upflow filtration is a more sensible filter method, which is characterized by large capacity for storage of solids, small head loss and long filter run. The main disadvantages of upflow filtration appear to be (a) the tendency for the expansion of the media because of increasing flow rates, (b) the difficulty of backwashing if layers of deposit accumulate at certain depths of the media.On the basis of former experience, further study about upflow filtration and have air-water backwashing have been conducted through pilot-plant test. In this article. optimum of the depth and grain size of the media is achieved. At the same time, the minimal grain size of the media and available head loss are also determined. In addition, the influence on the function of the upflow filtration caused by change of l/de ratio (in which 1 is the bed depth and de is the geometric mean size of the media) is discussed. Furthermore, the regularity of impurities removal, head loss of the filter and the variation of effluent turbidity have been studied. To solve the problem in upflow filtration that the fine grains at the top of medium are apt to be fluidized when the filtration rate is increased, feasible advices are proposed in this article. During the test. air-water backwashing is applied to upflow filtration for the first time. The best parameters of air-water backwashing are obtained through orthogonal tests, meanwhile, the most satisfying effect of air-water backwashing is decided by comparison. Thus, the difficulties in backwashing of upflow can be overcome successfully.