Concentration of Sludges by
Gravity and Pressure
BRIAN L. GOODMAN, Director
Technical Services
ROBERT B. HIGGINS, Manager
Ecodyne Corporation
Smith and Loveless Division
Affiliate of Trans Union Corporation
Lenexa, Kansas
INTRODUCTION
Probably the largest, most perplexing problem in the wastewater treatment
field today is sludge disposal. This problem has led to an extensive research program
by Smith and Loveless in the field of solids-liquid separation and solids dewatering
which, in turn, resulted in the development of a new wastewater sludge treatment
unit. Termed the S&L Sludge Concentrator, it utilizes a unique combination of
sludge conditioning, gravity dewatering, and pressure dewatering to greatly increase
the solids content of waste sludges prior to their final disposal. This concentrator
can, by increasing the solids content of waste sludges, both decrease the volume to be
transported and increase the ease with which sludge can be handled both during
trucking to the disposal area and final disposition by burial.
UNIT AND PROCESS DESCRIPTION
The S&L Concentrator was designed to take maximum advantage of the
characteristics of sludges which have been conditioned by synthetic, cationic, high
molecular weight polyelectrolytes. Such sludges are characterized by the rapid,
complete separation of their solid and liquid phases through the formation of
relatively large tough floe particles which display a high rate of sedimentation (20
ft/hr or more).
The Concentrator is equipped with a sludge feed pump, polymer system, high
rate thickener, and two stage dewatering unit (see Figure 1 and Figure 2). Sludge is
transported from its source by a variable speed diaphragm pump to the point of
polymer addition. Concentrated polymer solution is pumped from the polymer
mixing tank to a blending eductor by a metering pump. The concentrated polymer
solution is diluted by the blending eductor prior to the initial separation of solids and
liquid in the high rate sludge thickener. Overflow from the thickener is used in the
blending eductor for polymer dilution, and the underflow solids from the thickener
flow to the first stage of the dewatering unit.
The first stage of the dewatering unit employs an endless, variable speed,
relatively open mesh filter screen. The conditioned sludge is distributed substantially
horizontally to the moving screen with the result that the solids are retained on the
screen while the bulk of the remaining liquid passes through the screen. Solids from
the first dewatering stage pass on to the second stage of the dewatering unit. The first
stage screen is washed with spray water on its return trip to the distribution trough
so that a clean surface is always exposed to the conditioned sludge flowing from the
thickener. The open mesh filter screen facilitates complete washing.
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