Vacuum Filtration — Media and
Conditioning Effects
EDWIN R. BENNETT Assistant Professor
Department of Civil Engineering
University of Colorado
Boulder, Colorado
DAVID A. REIN, Lieutenant
U. S. Navy
DAVID J. DEVROY, Project Engineer
American Can Company
Green Bay, Wisconsin
INTRODUCTION
Over the last ten yr, there has been a steady and sizeable increase in the
application of vacuum filters for dewatering of wastewater sludges. This is true of
larger municipal operations where space limitations favor this form of mechanical
dewatering and for industrial applications for disposal of solid materials not
amenable to digestion.
Vacuum filtration equipment and operations have been passing through a
period of evolution with the major changes occurring in the type of filter media and
conditioning methods used. The early sewage sludge vacuum filters were similar to
those used in the starch industry. The filter media was a densely woven cotton cloth.
Modern waste treatment vacuum filters use a more open weave media selected for the
specific sludge application. Filter belts of wire mesh, synthetic fabrics or coil springs
in corduroy-like layers are available.
Selection of vacuum filtration equipment has been allocated, in many cases, to
the suppliers. Laboratory-scale testing with the Buchner funnel technique or the leaf
test apparatus can be used to establish the general range of filterability of the sludge,
although direct up-scaling to full size units is sometimes difficult. Some filter
manufacturers have pilot-scale equipment that can be transported to the waste
treatment plant and used to establish the filterability characteristics of the sludge.
These methods are used to select the filter equipment and media, without strong
emphasis on the conditioning chemical requirements. The effects of coagulant dose
and sludge septicity are very important and optimum operating characteristics must
be established on a continuous basis after the equipment has been installed.
Much of the vacuum filtration literature relates to optimization of conditioning
chemical dose. This is because the chemical dose is the major control parameter
available to the operator. The effect of the filter media on efficient operation has not
been as well described. It is the purpose of this study to investigate the
interrelationship of the filter media and the conditioning method on the operation of
vacuum filters used in waste treatment.
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