67    HIGH DENSITY SOLIDS FROM ACID WASTEWATER
TREATMENT
James B. Pfeiffer, Process Manager
TETRA Technologies, Inc.
Coraopolis, Pennsylvania 15108
INTRODUCTION
The imposition of stricter environmental limits on liquid effluents by RCRA has caused manufacturers to place greater emphasis on the operation of wastewater treatment facilities. There is a pressing
need for better control of liquid effluent quality, putting pressure on the operating personnel to assure
that effluent criteria are met. In the case of waste acid treatment, the concentrations of dissolved
metals, as well as total dissolved and suspended solids, must be accurately monitored and maintained
within the prescribed limits.
A natural consequence of removing metals from waste acids is the generation of metal hydroxide.
There is a need to minimize costs associated with the handling and disposal of these solid residues.
Typically, the solids that are generated by conventional neutralization processes settle poorly and
seldom attain solids concentrations greater than 5% upon gravity settling. At this concentration, 20
pounds of sludge must be discarded for each pound of solids generated. The reason for this gelatinous
mass is the occurrence of excessive water-bonding on the surface of the particles in conventional
processes, as illustrated (Figure 1).
It is common practice in the industry to dewater these settled sludges in either a plate-and-frame
filter press, belt filter or rotary vacuum filter press to produce a cake containing up to 25% solids. At
this higher concentration, only four pounds of sludge must be discarded for each pound of solids
generated.
Although these dewatering devices succeed in removing a considerable amount of water from the
sludge, cycling frequencies are low, compromising throughput, often requiring additional quantities
of supplemental body feed and demanding either large single processing units or several smaller units
to attain the capacity required to process all the sludge generated.
For a number of years, TETRA has operated dewatering equipment to enable clients to close
lagoons, and has relied on the dewatering capabilities of these devices while recognizing the need for
improving the handling and dewatering characteristics of sludges. Recently, TETRA acquired the
exclusive rights to a process that transforms low-density gelatinous metal sludges into a compact, high
density mass while the sludge is being generated.
Bonded Water
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.Causes Poor Sludge Concentration       __   ,	
■ Figure 1.    Excessive water bonding.
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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