The Use of Polymers For Improving Chemical
Sludge Dewatering on Sand Beds
JOHN T. NOVAK, Associate Professor
MARK LANGFORD, Graduate Student
Department of Civil Engineering
University of Missouri-Columbia
Columbia, Missouri 65201
INTRODUCTION
The dewatering characteristics of chemical sludges have received an increasing amount
of interest, primarily because of recent legislation affecting the discharge of water treatment
plant wastes. The wastes from water treatment are generated from a variety of processes and
vary widely as to their dewatering characteristics (1,2). Due to the wide variation in sludge
characteristics many processes have been suggested for sludge dewatering and drying.
Selection of a dewatering process will depend upon the site where the sludge is generated,
the characteristics of the sludge and the performance of the sludge dewatering facility.
Unfortunately we are unable to rationally compare sludge dewatering alternatives without
extensive pilot plant studies because process performance has not been sufficiently tied to
sludge characteristics to permit process comparisons.
In a recent study by Novak and Montgomery (3.) an attempt was made to relate sludge
performance on sand beds to the sludge characteristics. Of the factors which were found to
influence sand bed performance, the sludge specific resistance, r, and the sludge
compressibility as characterized by the coefficient of compressibility, s, had the greatest
influence.
The sludge specific resistance was found to influence the sludge drainage rate as shown
in Figure 1. For sludges which drain easily (low specific resistance) deep applications of
sludge could be made while those sludges which drained poorly (high specific resistance)
could only be applied at depths less than one foot if drainage was to occur in a reasonable
time.
Sludge compressibility was also found to influence sand bed performance. It was
observed by Novak and Montgomery that unless the value of the coefficient of
compressibility exceeded 0.7, penetration of sludge into and through the sand bed would
occur. When such penetration occurs frequent sand replacement is required and direct
filtrate discharge is not acceptable. The penetration data of Novak and Montgomery is
shown in Figure 2.
A recent study by Novak and O'Brien (4) has shown that inorganic polymer conditioning of chemical sludges results in a large decrease in the sludge specific resistance and
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