Review of Current Experimentation on
Dewatering of Paper Mill Sludges
W. L. CARPENTER, Regional Engineer
Kalamazoo, Michigan
N. J. LARDIERI, Research Engineer
National Council for Stream Improvement
New York, New York
INTRODUCTION
For some years the National Council for Stream Improvement has been engaged in a research program seeking more efficient methods for dewatering and
disposal of sludges resulting from the clarification of mill effluents. Basic laboratory work in this field has been conducted by Council projects at Rutgers University and more recently at Kalamazoo College. Extensive field testing of dewatering methods such as centrifuging has been carried on by Ohio member mills and
others. Major efforts on various phases of dewatering and disposal have also been
made by many individual companies.
A description of the physical characteristics of sludges resulting from effluent
clarification has been given by Gehm (1) who also reviewed the theory explaining
the high energy requirement needed todewater these sludges by mechanical means.
The more positive results of Council research on this problem have also been extensively reported (2,3,4). The present paper is in the nature of a progress report
on some of the more recent research at Kalamazoo College into methods which
appear to offer some promise of a more economical and technically feasible solution to the problem.
VACUUM FILTRATION WITH FLY ASH AS A FILTER AID
Preliminary work at this project (4) indicated that fly ash was a filter aid of
considerable promise in the dewatering of paper mill sludges. Vacuum filter rates
were improved in pilot tests of deinking sludge with fly ash aid and the dewatered
sludge volume was only slightly higher than where sludge was filtered alone. In
all cases, the cake discharge characteristics were materially improved. The
availability of fly ash as a waste product at many mill locations which normally
must also be disposed of enhances the attractiveness of this disposal method.
Subsequent research on this phase of dewatering has been devoted to ascertaining the effect of variables such as fly ash particle size distribution, filter rate,
and type of sludge on the process. The studies also developed basic information
regarding cake formation and discharge characteristics when using fly ash.
Conventional laboratory leaf test filter units, modified by the installation of
a two-inch circular shim between the clamp and the leaf, were employed for these
tests. This unit provided a means for building up a two-inch precoat on the leaf
which was equipped with a mono-filament nylon cloth face. All reference to precoat refers to a two-inch initial bed. A vacuum of 15 ins. of mercury was employed during both formation and drying cycles. Loading rates reported are for
cycle times (nitration and drying) of one min duration or fraction thereof.
Twelve samples of fly ash were collected from various mill power plants.
Sieve analyses were made of the dried samples and combustible matter varied from
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