• The Effectiveness of a Contact Filter for the Removal of Iron from Ground Water

      Kim, Steve W. (University of Alaska, Institute of Water Resources, 1971-01)
      Various types of modified filters were investigated to replace greensand filters which clogged when removing ground water. A properly designed uniform-grain sized filter can increase the filtration time more than ten times that of ordinary sand or greensand filters. The filter medium was obtained by passing commercial filter material between two standard sieves of a close size range, so that the resulting medium was of a uniform size. The head loss rate on such a medium was independent of the filter depth and was inversely proportional to the almost 3/2 power of the grain size. On the other hand, the filter depth was almost linearly proportional to the time of protective action. The effects of the grain size, filter depth, and filter material on the filter run were evaluated with a synthetic iron water; and optimum filter depths for each unisized material were determined. At identical filtration conditions, anthracite had a 70 to 110% longer filter run than the sand medium, and it was attributed to the greater porosity of the former. Expectedly, the time to reach initial leakage of the iron floc was greater with the coarse and more porous medium. but was reduced to an insignificant amount when the filter depth was increased to three to six feet. The performance of unisized filters on permanganate-treated ground water was much better than that of fine-grained greensand. Applicability of experimental data on an existing filtration theory was investigated