Environmental Engineering Reference
In-Depth Information
Introduction
We live on a planet with a surface that is three-fourths covered with water,
so we recognize the irony inherent in the fact that many areas of the world
face critical shortages of drinking water. Most of Earth's water is seawater,
of course—far too saline for human consumption. Of the little “fresh” water
that remains, most is trapped in polar ice caps, where harnessing it for use
is difficult. Much of the accessible natural supply of potable water is stressed
by a growing world population, which increases the basic demand for this
natural resource while reducing the supply further through contamina-
tion. Major population centers in developing nations (those without estab-
lished waste treatment or water treatment infrastructure) often suffer from
epidemics of waterborne disease. In these areas, raw sewage can directly
contaminate the rivers and streams used for drinking, washing, and cook-
ing. In other cases, unchecked industrialization leads to water contami-
nation through improperly disposed of chemical and nuclear wastes. The
drinking water purveyor must ensure that the drinking water supplied is
safe for human consumption. In fact, the primary reason for the develop-
ment and installation of a public water system is the protection of public
health. Basically, a properly operated water system serves as a line of defense
between disease and the public. Properly operated water treatment and sup-
ply systems are defined as those that
• Remove or inactivate pathogenic microorganisms including bacte-
ria, viruses, and protozoans
• Reduce or remove chemicals that can be detrimental to health
• Provide quality water, thus discouraging the customer from seeking
better tasting or better looking water that may be contaminated
This last point is critical, but one often overlooked in the operation and
management of public water systems. When the water produced by a system
is objectionable because of odor, taste, or appearance, customers will seek
another source for their drinking water. Ironically, these alternative sources,
although they look, taste, and smell fine (“better than city water”), could
contain microorganisms or chemicals that are harmful. In this chapter, we
discuss the drinking water practitioner's most important function: ensuring
that water delivered to the public is properly treated and arrives as the clean,
wholesome, safe product that it must be.
A typical water treatment plant treats stream or river water (turbid surface
water with organics) and processes the raw water using various unit pro-
cesses, including: (1) screening, (2) coagulation, (3) flocculation, (4) sedimenta-
tion or settling, (5) filtration, (6) hardness treatment, (7) disinfection, and (8)
fluoridation (see
Figure 11.1
). This chapter provides a brief overview of each
