University of Alaska, Institute of Water Resources
Abstract
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 investigatedThe work upon which this report is based was supported by funds (Proj.
A-025-ALAS) provided by the United States Department of the Interior, Office of
Water Resources Research, as authorized under the Water Resources Act of 1964
