A Practical Approach
to the Environmental Effects of
Thermal Discharges
LAWRENCE P. BEER,   Director
Environmental Sciences Division
Industrial Bio-Test Laboratories
Northbrook, Illinois
WESLEY O. PIPES, Professor
Department of Civil Engineering
Northwestern University
Evanston, Illinois
INTRODUCTION
Public and professional concern over the possible deleterious effects of waste
heat in aquatic environments has been mounting rapidly in the last few years. Estimates of the present and projected magnitude of the problem vary with projections of
future cooling water requirements. According to the Federal Water Pollution Control
Administration (1), industrial cooling water usage in the United States in 1964
amounted to more than 50 trillion gal with more than 40 trillion gal being used by
the electric power industry alone. Electric power generation is increasing at a rate of
7.2 per cent annually and this rate is expected to increase (2). Cooling water usage by
other industries and for commercial and industrial air conditioning is also increasing.
Thus,   in   quantitative   terms,  there  is good  reason  for  the  increasing  concern.
The present major demand for cooling water is from the power industry and
this demand has been extrapolated to give projected future demands. According to a
forecast (3), electric power use is expected to be 1,503 billion kw hr in 1970 and to
increase to 2,022 in 1975, 2,754 in 1980, and 3,639 in 1985. Heat rejection by
thermal electric plants varies between 5,000 and 10,000 Btu/kw hr. The amount of
cooling required for power plants in 1980 will be between 13,870 and 27,540 trillion
Btu. Based on present-day powerplant technology and design, this waste heat must be
discharged to the environment in some form.
Air cooling systems for large power plants are feasible but very expensive and
they consume an appreciable fraction of the power produced by the plant. Evaporative water cooling devices include cooling ponds, aerators, agitators, natural draft
cooling towers, and mechanical draft cooling towers. Evaporative cooling towers are
proportionally less expensive than dry cooling towers, however, they are very expensive and represent a consumptive water use. The use of cooling ponds for a power
plant is equivalent to buying or building a lake solely to use as a heat sink. The same
types of problems occur in these ponds as those which occur in natural lakes and
streams but usually in an intensified form. Likewise, if the cooling pond needs to be
constructed, the cost may be prohibitive.
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