Freeze Conditioning of Waste Activated Sludge
TIMOTHY TILSWORTH, Assistant Professor and Head
Program of Environmental Health Engineering
R. SAGE MURPHY, Director
Institute of Water Resources
University of Alaska
College, Alaska
LARRY E. GARINGER. Sanitary Engineer
Manitoba Department of Mines, Resources, and Environmental Management
Winnipeg, Manitoba
Canada
JAN WAGNER, Doctoral Student
University of Kansas
Lawrence, Kansas
INTRODUCTION
Ultimate disposal of wastewater sludge has long been a problem which to a large degree
has been ignored. Haney (I) in 1971 stated that: "Until process sludge can be handled with
minimum environmental impact, we cannot claim to have a viable wastewater treatment
process." The relationship of sludge disposal to total treatment processes is emphasized by
noting that sludge handling and disposal represents up to 50 percent of the total treatment
capital and operating costs (2). Processing of wastewater sludge will, no doubt, receive
increased attention in the future because of environmental concerns for our air, land and
water.
Present technology for processing wastewater treatment plant sludge is well
established and includes conditioning, dewatering, and disposal. Many of these processes
are highly sophisticated and relatively expensive. Most of the more advanced processes are
unsuitable for small wastewater treatment facilities in Alaska.
The extended aeration modification of activated sludge has been widely used as a small
unit biological waste treatment process. Although several types of waste treatment
processes have been constructed and operated with varying degrees of success in the remote
regions of Alaska, the extended aeration modification appears to be one of the most
promising systems available. Nonetheless, extended aeration, as with most biological waste
treatment processes, produces more activated sludge than can be auto-oxidized within the
aeration chamber. The excess activated sludge is an inherent characteristic which is well
documented in the literature (3,4,5). Excess sludge from extended aeration activated sludge
is, in many instances, intentionally discharged with the plant effluent. Even though the
material is well oxidized it can be detrimental to the receiving stream, particularly during
winter months when many of Alaska's streams have relatively little flow. It is anticipated
that regulatory agencies will prohibit such disposal practices in the future.
Many solutions to the sludge disposal problem have been developed but most are
either uneconomical for the small installations or are unfeasible for the severe
climatological conditions inherent to Alaska. The presently used processes of vacuum
filtration, incineration, and centrifugation are satisfactory but too expensive for the small
plants found in Alaska which are generally in the 500 - 5000 population equivalent range.
One solution to waste sludge disposal which appears feasible for small installations in
Alaska consists of a combination of conventional sand drying beds and the freeze-thaw
technique. Research on the freezing and thawing of sewage sludge has shown that this
technique yields sludge having good dewatering characteristics (2). This fact, coupled with
Alaska's natural refrigeration, suggests the potential for use of the process in cold regions.
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