Polyelectrolytes in
Industrial Waste Treatment
ROBERT B. SCHAFFER, Technical Service Representative
The Dow Chemical Company
Midland, Michigan
INTRODUCTION
The use of synthetic organic polyelectrolytes or polymers in waste treatment
for process improvement in all solids-liquid separations is being explored and advocated by a number of chemical producers and waste treatment specialists. Such
chemicals have proven themselves valuable in a number of applications for many
years but not until recently have they come into their own in the many and varied
solids-liquid separation processes in waste treatment.
Solids removal is important in all treatment operations since it is, more often
than not, a qualitative measure of treatment efficiency or an effluent requirement.
Solids are also of indirect importance in their relationship to BOD. Since this
paper discusses industrial waste treatment, each type of solid and each type of
waste must be considered as a separate problem. Factors such as pH, ionic charge,
temperature, solids concentration and many others make it virtually impossible for
one particular chemical to apply in each instance. Because of these variations,
the PURIFLOC flocculants were developed by the Dow Chemical Company. The
application of these materials will be discussed in this presentation.
These flocculants will agglomerate a wide variety of inorganic and organic
solids, including colloids, which are present in waste waters. They are intended
exclusively for use in water and waste water treatment for enhancing solids-liquid
separations in clarification, filtration, and thickening processes. These flocculants are all high molecular weight, water soluble, synthetic organic polymers.
They are described in relation to their ionic character in solution in Table I. Due
to the variation in molecular weight and ionic character, one of these flocculants
will, in most every instance, improve a solids-liquid separation system.
Some of the descriptions and data included in this paper are limited due to
the proprietary nature of the information, and in some instances, the lack of desired sampling and analysis. It is common practice in many industrial waste treatment plants to operate with as little control as possible and much of the data that
we would like to have to completely evaluate plant operations are simply not
available. Therefore, it is the intent of this paper to provide an insight into the
possible applications of polyelectrolytes in industrial waste treatment.
Meat Packing
Laboratory and pilot studies using polymers for the operational improvement
of an anaerobic contact process used by Wilson and Company in Albert Lea, Minnesota, were encouraging enough to warrant a full-scale trial. Fortunately, the
1.7 MGD treatment plant was constructed in parallel so that it was possible to treat
one-half of the plant with polymer and use the other half as a control.
The plant (Figure 1) is equipped with a raw waste equalizing tank to provide
storage for equalizing the flow over a full 24-hr period. Digestion takes place in
two concrete digesters with gas tight concrete covers into which the raw wastes,
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