Page 321 - Water Engineering Hydraulics, Distribution and Treatment

299
10.3 Public Health Issues and Drinking Water Treatment
Legionella, which are aerobic, non-spore forming, typi-
in 1940 in which about 30,000 cases of mild enteritis and 5
cases of typhoid fever followed the inadvertent opening of
a valve serving an emergency connection between the pol-
severe epidemic of pneumonia at an American Legion con-
luted industrial water supply of the city and its drinking water
vention in 1976. The incident led to the isolation and char-
acterization of the pathogenic bacteria, L. pneumophila.
supply. From 1946 to 1960 there were, in the United States,
In the spread of schistosomiasis, which results from the
39 outbreaks of waterborne typhoid fever, 11 outbreaks with
improper disposal of human feces, infection of man does
563 cases of shigellosis, and 4 outbreaks with 24 cases of
not take place in the water itself, but when larvae released
salmonellosis. In Madera, CA, in 1965, both shigellae and
salmonellae were implicated in an outbreak of 2,500 cases of
by their snail hosts are forced into the skin from shrinking
infection traced to the contamination of a well by irrigating
water droplets as bathers or waders emerge from infected
an adjacent pasture with unchlorinated wastewater effluent.
waters. Because the United States and Europe are free from
The attack rate was as high as 53.6% for water drawn from a cally flagellated, gram-negative bacteria, were named after a
the specific snail hosts of pathogenic schistosomes,theyare
370 ft (113 m) well. also free of schistosomiasis. However, the snail hosts and
At the turn of the last century the annual death rate from larvae of schistosomes that cause swimmer’s itch, a skin dis-
typhoid fever still averaged 30 per 100,000 in US communi- ease (cercarial dermatitis), do occur in some parts of the
ties. By that time the principal epidemic focus of cholera had United States. They are transported from one body of water
more or less retreated to Bengal (India and East Pakistan), to another by infected water fowl.
where cholera could retain a foothold because of favorable Of the few reasonably well-documented waterborne out-
climatic and social conditions. After the chlorine compounds breaks of virus infections, two possibly waterborne outbreaks
(1908 in the United States) and the chlorine itself (1911 in the of poliomyelitis in the United States and Canada, and the
United States) were dosed to water for disinfection, the inci- apparently waterborne outbreak of infectious hepatitis at
dence of waterborne typhoid fever was driven substantially New Delhi, India, in 1955–1956, are commonly listed in
to the vanishing point at less than 1 per million in orga- the epidemiological roster.
nized communities of the United States and Europe. Records At the beginning of the industrial revolution, chlori-
of waterborne paratyphoid, namely, typhoid-like fevers or nation was the only drinking water treatment technology
salmonelloses, are few. used for the sole purpose of disinfection. Today disinfection
In the case of ameba, or amoeba, only three major water- remains to be the most important process among all water
borne epidemics of amebic dysentery are on record in the treatment processes and has been significantly improved in
United States. The first was confined to the patrons of two terms of having more disinfection alternatives and more effi-
hotels; the second, to firemen and spectators at a stockyard cient disinfectant by-product control.
fire; and the third, to workers in an industrial establishment. The widespread use of synthetically produced organic
In the period from 1946 to 1960 there were 2 outbreaks with and inorganic chemical compounds, including pesticides,
36 cases. insecticides, polychlorinated biphenyls (PCBs), gasoline,
Giardiasis is a diarrheal illness caused by a microscopic pharmaceutical compounds, and industrial compounds con-
parasite, Giardia intestinalis (also known as Giardia lam- taining heavy metals and volatile substances, has required
blia). Once a person or animal has been infected with Giar- the use of additional water treatment technologies, such
dia, the parasite lives in the intestine and is passed in feces. as aeration, chemical precipitation, coagulation, sedimenta-
Because the parasite is protected by an outer shell, it can tion, flotation, filtration, carbon adsorption, ion exchange,
survive outside the body and in the environment for long ozonation, and membrane filtration, for drinking water
periods of time. During the past two decades, Giardia infec- production.
tion has become recognized as a common cause of water- Substances that alter the quality of surface water or
borne disease in humans in the United States. Giardia can groundwater may be classified under four major categories:
be found worldwide and within every region of the United (1) physical, (2) chemical, (3) biological, and (4) radiologi-
States. cal. The four categories and the US and international drink-
Cryptosporidium is resistant to chemical disinfectants, ing water standards (World Health Organization (WHO),
remains viable in raw water for extended periods of time, Canada, and Mexico) are presented in subsequent sections
and has been identified as a leading cause of waterborne dis- when available. All drinking water standards require not only
ease outbreaks in the United States in recent decades. Since inactivation of pathogenic microorganisms, but also removal
Cryptosporidium is smaller than Giardia and more resistant of toxic or undesirable impurities listed in the drinking water
to chemical disinfectants than Giardia, it is assumed that if standards. Section 10.8 discusses the drinking water stan-
the required Cryptosporidium level of water treatment can be dards in detail. It should be noted that the drinking water
achieved then the required Giardia level of water treatment standards are similar to any other laws, which are subject to
can also be achieved. Cryptosporidium, at 3–5 microns, is change from time to time. The reader should always search
physically smaller than Giardia with a size of approximately for and use the latest local drinking water standards for water
5–15 microns. quality control.