The Disposal of Waste Brine from
Desalting Operations
WILLIAM F. McILHENNY, Associate Scientist
M. A. ZEITOUN, Research Specialist
PAUL G. LeGROS, Senior Research Engineer
The Dow Chemical Company
Freeport, Texas
INTRODUCTION
An increasing number of communities and industries are being forced to seek
additional or alternate sources of fresh water and are finding insufficient resources of
good quality water to supply the demand. Desalination of brackish or saline water is,
in many cases, the most economical method of extending water resources to supply
these increasing demands.
A necessary accompaniment to the product water is a waste stream containing
in a more concentrated solution all or almost all of the soluble salts that made the
original feed stream unusable. The disposal of this waste brine in such a manner as to
minimize damage to the environment presents a problem with serious economic,
engineering and legal aspects.
The salt content of any effluent brine will consist almost entirely of some
combination of the same seven ions: sodium, potassium, calcium, magnesuim, chloride, sulfate, and bicarbonate, whether the original source was the ocean, an inland
saline water, or an underground brine. In addition, the waste will contain any materials either intentionally or unavoidably added during the desalination process. Heat is
also an additional environmental stress contained in the waste stream when power is
generated or when the desalination process is thermally driven.
The effluents are troublesome because it is these simple inorganic constituents
that originally rendered the feedwater unusable. They cannot easily be converted
into harmless substances since the amounts are large and the constituents have little
instrinsic value.
The entire water system must be examined to determine the actual cost of
water and to realistically appraise the effects of disposal. The entire system includes
the acquisition of the raw water from whatever source, the pretreatment, if necessary
to allow desalting, desalination itself, post treatment and disposal by one or more
methods.
At coastal locations, where seawater is available both as a feed and as a disposal
sink, an obvious method of disposal is through an outfall located in tide water
(Figure 1). The amount of salt on the land is not increased and the effects of brine
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