Environmental Engineering Reference
In-Depth Information
water before us and we perceive a full glass of crystal clear, refreshing water,
what we are really seeing is a concoction of many chemicals mixed with
water, forming the chemical cocktail.
The most common chemical additives used in water treatment are chlo-
rine, fluorides, and flocculants. Because we have already discussed fluorides,
we focus our discussion in the following sections on the byproducts of chlo-
rine and flocculant additives.
byproducts of Chlorine
To lessen the potential impact of that water cocktail, the biggest challenge
today is to make sure that the old standby, chlorine, will not produce as
many new contaminants as it destroys. At the present time, arguing against
the use of chlorine is difficult. Since 1908, chlorine has been used in the
United States to kill off microorganisms that spread cholera, typhoid fever,
and other waterborne diseases. In the 1970s, however, scientists discovered
that, although chlorine does not seem to cause cancer in lab animals, when
used in the water treatment process it can create a long list of byproducts
that do. The byproducts of chlorine that present the biggest health concern
are organic hydrocarbons, known as
trihalomethanes
, which are usually dis-
cussed as total trihalomethanes (TTHMs).
The USEPA classifies three of these trihalomethane byproducts—chlo-
roform, bromoform, and bromodichloromethane—as probable human car-
cinogens. The fourth, dibromochloromethane, is classified as a possible
human carcinogen. The USEPA set the first trihalomethane limits in 1979.
Most water companies met these standards initially, but the standards were
tightened after passage of the 1996 Safe Drinking Water Act (SDWA) amend-
ments. The USEPA is continuously studying the need to regulate other can-
cer-causing contaminants, including haloacetic acids (HAAs), also produced
by chlorination.
Most people concerned with protecting public health applaud the USEPA's
efforts in regulating water additives and disinfection byproducts; how-
ever, some people involved in the water treatment and supply business
have expressed concern. A common concern often heard from water utili-
ties having a tough time balancing the use of chlorine without going over
the regulated limits revolves around the necessity of meeting regulatory
requirements by lowering chlorine amounts to meet byproducts standards
and at the same ensuring that all the pathogenic microorganisms are killed
off. Many make the strong argument that, although no proven case exists that
disinfection byproducts cause cancer in humans, many cases—an extensive
history of cases—show that if we do not chlorinate water, then people get
sick and sometimes die from waterborne disease.
Because chlorination is now prompting regulatory pressure and compli-
ance with new, demanding regulations, many water treatment facilities are
looking for other options. Choosing an alternative disinfection chemical
