Encyclopedia of Environmental Science and Engineering, Volume I and II

536 INDUSTRIAL WASTE MANAGEMENT

Power Generation Industry

The power generation industry uses large volumes of

water for cooling purposes. It is estimated that total cool-

ing water demand for power generation is in excess of

400 billion cubic meters per year. This is approximately

one-fifth of the total runoff in the United States.^33 Direct

discharge of cooling water in streams, lakes, and estuaries

has an impact on water quality and the ecosystem in three

ways: it pollutes the water thermally, it subjects aquatic

organisms to a variety of physical stresses as it is pumped

through the plant, and it pollutes the water chemically.

Types of Cooling Systems

Basically, there are three ways of dissipating heat: once

through cooling systems, cooling ponds, and cooling towers.

The average condenser water requirement and consumptive

use for different cooling systems are summarized below:^36

Condenser requirement 120 liters per KWH

Consumptive use:

once through 0.7 liter per KWH

cooling ponds 1.0 liter per KWH

cooling tower 1.4 liter per KWH

A general discussion on three types of heat dissipating

systems is given below:^37

Once Through Cooling The most common and least

expensive method for removing heat from power plant

condensers is a once-through-cooling system. The system

requires large intake structures and has the largest environ-

mental impact. Aquatic organisms are forced through the

condenser tubes resulting in high mortality. The 2 to 5°C

warmer discharge upsets stratification, lowers dissolved

oxygen, increases the metabolic rate of aquatic animals, and

increases undesired bacteria.

Cooling Ponds The cooling water is circulated through

cooling ponds in a closed-loop. Cooling occurs by evaporation,

conduction, and long-wave radiation. Land area of the ponds

are generally 0.5–1 hectare/MW.

Cooling Towers Cooling towers are used to eliminate

discharge of heated water into natural bodies of water.

There are two types of cooling towers: natural-draft and

mechanical-draft. Natural-draft cooling towers rely on

natural air circulation to dissipate waste heat to the atmo-

sphere. The mechanical-draft cooling towers use induced

drafts to promote evaporative heat transfer. Both require

heat transfer between water and air. Dry cooling towers use

a temperature driving force between the water inside the

tubes and air flowing past the tubes.

Wastewater Treatment

Chemical discharges from the power-generation industry result

from makeup water treatment; chemicals added to plant cool-

ing water or steam generator; products of corrosion, erosion,

wear, or chemical reaction from plant system; and residuals

from pollution control equipment. The chemicals generally

controlled in effluent discharge permits are: pH, PCBs, TSS,

oil and grease, heavy metals, free and total residual chlorine,

phosphorus, and corrosion inhibitors.^34 Treatment methods

generally used for removal of contaminants include: neutral-

ization, coagulation, and precipitation of corrosion inhibitors,

TSS, heavy metals and phosphorus; flotation or American

Petroleum Institute (API) separator for oil and grease; ion-

exchange or reverse osmosis for TDS control; and evaporation

for concentration and residue recovery and disposal.

REFERENCES

1. Henry Lee, Legislation and Standards: Status, Trends Significance,
   Chapter 1, “Industrial Wastewater Management Handbook”, H.S. Azad
   (Editor), McGraw-Hill Book Co., New York, 1976.


2. Qasim, S.R., Wastewater Treatment Plant: Planning Design and Opera-
   tion, Technomic Publishing Company, Inc. Lancaster, PA, 1994.


3. Federal Water Pollution: Control Act Amendment of 1972 (PL 92-500),
   92nd U.S. Congress, October 18, 1972.


4. Clean Water Act (PL 95-217), 95th U.S. Congress December 27, 1977.


5. Wentz, C.A., Hazardous Waste Management, McGraw-Hill Book Co.,
   New York, 1995.

TABLE 8

Origin, characteristics, and treatment of wastes in four major metal industries

Industries Producting Wastes Origin of Major Wastes Major Characteristics Major Treatment and Disposal Methods

Steel Coking of coal, washing of

blast-furnace flue gases,

and pickling of steel

Low pH, acids, phenol, ore, coke,

limestone, alkali, oils, mill

scale, and fine suspended solids

Neutralization, recovery and reuse,

chemical coagulation

Iron-foundry products Wasting of used sand by

hydraulic discharge

High suspended solids, mainly

sand; some clay and coal

Selective screening, drying of reclaimed

sand

Metal container Cutting and lubricating metals,

cleaning can surface

Metal fines, lubricating oils,

variable pH, surfactants,

dissolved metals

Oil separation, chemical precipitation,

collection and reuse, lagoon storage.

Final carbon adsorption

Metal-plated products Stripping of oxides, cleaning and

plating of metals

Acid, metals, toxic, low volume,

mainly mineral matter

Alkaline chlorination of cyanide;

reduction and precipitation of

chromium; lime precipitation of

other metals

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