Transcript Freeman 1e: How we got there

CHAPTER 28
Wastewater Treatment, Water Purification,
and Waterborne Microbial Diseases
Wastewater Microbiology and
Water Purification
Public Health and Water
Quality
• Microbial culture methods for evaluating the
health significance of polluted drinking water
were not practiced until coliform-counting
procedures were developed and adapted in
about 1905.
• Until then, water purification was limited to
filtration to reduce turbidity. Although
filtration significantly decreased the microbial
load of water, many microorganisms still
passed through the filters. In about 1910,
chlorine was discovered to be an extremely
efficient disinfectant for large water supplies.
• Drinking water quality is determined by
counting coliform bacteria. Strict adherence to
uniform microbiologic standards makes this
method a reliable and reproducible indicator
of fecal contamination in all public water
supplies in the United States.
• Filtration and chlorination of water supplies
significantly decreases microbial load.
Application of water purification methods to
drinking water is the most important public
health measure ever devised (Figure 28.2).
Wastewater and Sewage
Treatment
• Wastewater enters a treatment plant and,
following treatment, the effluent water—
treated wastewater discharged from the
wastewater treatment facility—is suitable for
release into surface waters such as lakes and
streams or to drinking water purification
facilities.
• Wastewater treatment is primarily concerned
with treating sewage and industrial wastes to
reduce the biochemical oxygen demand
(BOD) to acceptable levels.
• Figure 28.3 diagrams
wastewater treatment processes.
• Primary, secondary, and tertiary
wastewater treatment involves physical,
biological, and physicochemical processes.
• Figure 28.5 shows anoxic secondary
wastewater treatment, and Figure 28.6
shows aerobic secondary wastewater
treatment processes.
• After secondary or optional tertiary
treatment, water may be suitable for release
directly to a water purification plant.
Drinking Water Purification
• Drinking water plants employ industrialscale physical and chemical systems that
remove or neutralize biological, inorganic,
and organic contaminants from a variety of
natural, community, and industrial sources.
• To further ensure that residual chlorine
levels are maintained throughout the
distribution system, most municipal water
treatment plants also introduce ammonia gas
with the chlorine to form the stable,
nonvolatile chlorine-containing compound
chloramine.
• Figure 28.8 traces the flow of raw water (untreated
water) through a typical treatment scheme.
• Raw water is first pumped from the source
to a sedimentation basin where anionic
polymers, alum (aluminum sulfate), and
chlorine are added. After mixing, the particles
continue to interact, forming large, aggregated
masses, a process known as flocculation.
• Sediment, soil, sand, mineral particles, and
other large particles settle out. The sedimentfree water is then pumped to a clarifier
(coagulation basin), a large holding tank
where coagulation takes place.
• The alum and anionic polymers form large
particles from the much smaller suspended
solids. The resulting water is potable,
finished water, free of chemical and
biological contamination.
Waterborne Microbial Diseases
Sources of Waterborne
Infection
• Drinking water and recreational water may
both be sources of waterborne pathogens. In
the United States, the number of disease
outbreaks due to either of these sources is
relatively small in relation to the large number
of exposures to water (Tables 28.1, 28.2).
• Worldwide, lack of adequate water treatment
facilities and access to clean water contribute
significantly to the spread of infectious
diseases.
Cholera
• Vibrio cholerae is a pathogen that causes
cholera, an acute diarrheal disease resulting in
severe dehydration.
• Cholera occurs in pandemics. The current
pandemic has endemic foci in the Americas,
the Indian subcontinent, Asia, and Africa. In
endemic areas, appropriate precautions to
avoid contaminated water and food are
reasonable preventive measures.
• Oral rehydration and electrolytes are the most
efficient and effective ways to treat the disease,
reducing overall mortality to about 1%.
Giardiasis and
Cryptosporidiosis
• Giardiasis and cryptosporidiosis are spread
by the chlorine-resistant cysts of Giardia
intestinalis and Cryptosporidium parvum,
respectively, in drinking water and
recreational water contaminated by the feces
of infected humans or animals.
• Infection with either parasite causes diarrhea
and may lead to more serious disease in
compromised individuals.
Legionellosis (Legionnaires’
Disease)
• Legionella pneumophila is a respiratory
pathogen that causes legionellosis and
Pontiac fever. L. pneumophila grows to high
numbers in warm water and is spread via
aerosols. The prevalence of legionellosis is
not decreasing, and infections are
underreported.
Typhoid Fever and Other
Waterborne Diseases
• Typhoid fever, viral infections, and
amebiasis are important waterborne diseases.
Waterborne typhoid fever and viral illnesses,
although still common diseases in developing
countries, have been controlled by effective
water treatment in developed countries.
• Amebic dysentery caused by Entamoeba
histolytica is a worldwide problem that affects
millions of people. Meningoencephalitis is a
rare but serious condition caused by
Naegleria amebiasis.