Coarse Media Reverse Grain Filtration Technique And Its Application To Drinking Water Treatment

Filtration is one of the key technique for water treatment. Since the reverse grain filtration can overcome most of the problems of the tradition downstream filtration in theory, it has been believed to be a long term potential water filtration. However, there has been not obvious evolution for this technique both in theory and application. Based on previous results, this study has made a detailed investigation to this technique and has solved most of the problems of the reverse grain filtration using the method of increasing the grain size and changing the grain proportion with different sizes of the filter medium through laboratory simulation and in situ production tests. The concept of coarse media reverse grain filtration and its technique parameters has been suggested. The results have shown that there are some important advantages of the coarse media reverse grain filtration over tradition downstream filtrations, such as a larger accepted capability for pollutant, a larger amount of water production, a stronger reverse washing intensity, a longer working period, a clearer washing of filter medium, and a significant saving of investment. Under the conditions of the coarse quartz sand filter medium with a grain size of 0.63-1.60mm or 0.71-2.00mm and a thickness of 82-85 cm, and a turbidity of 30 NTU for filtrating water, a good treatment result has been obtained: an 16 m/h average filtration speed, a less than 1NTU turbidity for filtrated water, and a 14-24 h long filtration cycle, and an over 90% removal for suspend grain, organic matter, bacterium and coliform group. Its filtration speed is 1.5 time of the normal fast filter cell, but its size has reduced to 2/3. The coarse media reverse grain filtration technique has wide application to not only new water plants reconstruction, older water plant alteration, but also to treatment of some source waters highly polluted by iron, manganese or organic matter.