Water Resources Research Center, University of Minnesota
Newsletter or Bulletin
The use of a spherical buoyant media in filtration has many potential
advantages. The media stratify during backwashing such that the largest
spheres are at the top of the bed and the smallest are at the bottom.
During upflow filtration solids may be removed by both straining on the
underside of the filter and by depth filtration. The accumulated solids
may be readiiy dislodged by a brief downflow backwash and gravity assists
i n this cleaning process.
Basic studies on the removal of coagulated clay suspensions indicated that
the clay was removed throughout the depth (D.3m) of the filter for media
sizes between 0.6 and 1.0 mm. Straining was not observed to be significant
but it would become more important for smaller media sizes or more flocculant
solids. Headloss development was monitored and followed the expected behavior
for depth filtration. Low headlosses could be maintained by using shallow
bed of media and backwashing frequently.
These preliminary studies indicate that if the buoyant media are to be used
in an effective low energy filter, the system design wi11 be very important.
A straining mechanism may be preferred since the solids are retained on the
underside of the filter and gravity wi1'l assist in cleaning the bed during
backwash. However, to avoid rapid headloss development depth filtration
must be used also.
Additional studies are needed to characterize the backwashing behavior of the
media and to identify the best operating strategies for long-term use.
Brezonik, P. Chiesa, S. Semmens, M.J. 1983. Low Energy Filtration Using Buoyant Media. Water Resources Research Center.
Water Resources Research Center
Brezonik, P.L.; Chiesa, S.; Semmens, M.J..
Low Energy Filtration Using Buoyant Media.
Water Resources Research Center, University of Minnesota.
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