46    A FIELD EVALUATION OF VACUUM ASSISTED SLUDGE
DEWATERING BED SYSTEMS
Arthur J. Condren, Principal Engineer
James M. Montgomery, Consulting Engineers, Inc.
Pasadena, California 91109
Alfred T. Wallace, Professor
Department of Civil Engineering
University of Idaho
Moscow, Idaho 83843
Ivan A. Cooper, Assistant Vice President
HDR Infrastructure
Denver, Colorado 80203
James F. Kreissl, Environmental Engineer
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
INTRODUCTION
The vacuum assisted sludge dewatering bed (VASDB) process was developed in the mid-1970s as an
alternative to conventional sludge drying beds and other dewatering technologies normally utilized at
small-to medium-sized wastewater treatment facilities. There are currently about 100 VASDB installations in the U.S. for dewatering a wide variety of sludges. About 25% of these systems have been in
operation long enough to provide a meaningful data base for judging their performance and both
capital and O&M costs. During the spring and summer of 1985, a field evaluation of twelve operational VASDB systems was conducted. Data were collected on several other operating systems by
telephone contacts. Additional information was obtained from the known manufacturers of VASDB
systems, each of whom was visited or otherwise contacted in conjunction with this study.
Sludges which have been successfully dewatered on these systems include:
1. Aerobically digested sludge
2. Anaerobically digested sludge
3. Undigested secondary sludges from
a. Oxidation ditches
b. Extended aeration plants
4. Mixtures of undigested secondary sludge plus alum or lime treated primary sludge
5. Imhoff tank sludge
6. Water treatment plant alum sludge
7. Metal hydroxide sludge
PHYSICAL DESCRIPTION
The "heart" of the system is the rigid media plate. It consists of a layer of gravel, bonded together
with epoxy and topped with a level layer of epoxy-bonded material of smaller particle size. Figure 1 is
a cross section through a "typical" plate.
The media plates are placed either directly on a flat or slightly sloped concrete support slab or on a
compacted and leveled gravel layer above a concrete support slab. Once the plates are arrayed on the
bed and leveled, they are bonded together to form an integral media surface. As the plates are subject
to thermal expansion and contraction, the inclusion of expansion joints in the design of VASDB
systems is important, especially for those systems which will not be contained in a building. At a
minimum, the expansion joint should encompass the entire perimeter of the bed, placed between the
concrete containment walls and the edges of the abutting media plates. The expansion joint should
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