Science of Water : Concepts and Applications

9
Water Treatment
If you visit American city,
You will fi nd it very pretty.
Just one thing of which you must beware:
Don’t drink the water…
INTRODUCTION *
—T. Lehrer (1966)
He wandered the foggy, fi lthy, corpse-ridden streets of 1854 London searching, making notes,
always looking … seeking a murdering villain—and fi nd the miscreant, he did. He took action; he
removed the handle from a water pump. And, fortunately for untold thousands of lives, his was the
correct action—the lifesaving action.
He was a detective—of sorts. No, not Sherlock Holmes—but absolutely as clever, as skillful, as
knowledgeable, as intuitive—and defi nitely as driven. His real name: Dr. John Snow. His middle
name? Common Sense. Snow’s master criminal, his target—a mindless, conscienceless, brutal
killer: cholera.
Let us take a closer look at this medical super sleuth and at his quarry, the deadly killer
cholera—and at Doctor Snow’s actions to contain the spread of cholera. More to the point, let us
look at Dr. Snow’s subsequent impact on water treatment (disinfection) of raw water used for potable
and other purposes.
DR. JOHN SNOW
Dr. John Snow (1813–1858), an unassuming—and creative—London obstetrician, achieved prominence
in the mid-19th century for proving his theory (in his On the Mode of Communication of
Cholera) that cholera is a contagious disease caused by a “poison” that reproduces in the human body
and is found in the vomitus and stools of cholera patients. He theorized that the main (although not
the only) means of transmission was water contaminated with this poison. His theory was not held in
high regard at fi rst because a commonly held and popular countertheory stated that diseases are transmitted
by inhalation of vapors. Many theories of cholera’s cause were expounded. In the beginning,
Snow’s argument did not cause a great stir; it was only one of many hopeful theories proposed during
a time when cholera was causing great distress. Eventually, Snow was able to prove his theory. We
describe how Snow accomplished this later, but for now, let us take a look at Snow’s target: cholera.
Cholera
According to the U.S. Centers for Disease Control and Prevention (CDC), cholera is an acute, diarrheal
illness caused by infection of the intestine with the bacterium Vibrio cholera. The infection
is often mild or without symptoms, but it sometimes can be severe. Approximately 1 in 20 infected
persons have severe disease symptoms characterized by profuse watery diarrhea, vomiting, and leg
cramps. In these persons, rapid loss of body fl uids leads to dehydration and shock. Without treatment,
death can occur within hours.
* Adapted from Spellman, F.R., Choosing Disinfection Alternatives for Water/Wastewater Treatment, Boca Raton, FL,
CRC Press, 1999.
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