Water Pollution
Chapter 20
Dave Sang
Nora Tibbetts
20-1
What are the Causes and
Effects of Water Pollution?
Causes of Water Pollution
 Water pollution - any chemical, biological, or
physical change in water quality that harms
living organisms or makes water unsuitable for
desired uses.
 Agricultural activities - leading cause
 Industrial facilities
 Mining
 Parking lots
 Widespread use of human-made materials
(plastics, etc.)
 Climate change as a result of global warming
Point Sources
 Point sources - discharge pollutants at
specific locations through drain pipes,
ditches, or sewer lines into bodies of
surface water.
 Examples: factories, sewage treatment
plants, underground mines, oil tankers
 Located at specific places, and are easy
to identify, monitor, and regulate.
 Many developed countries have laws
that help to control point-source
pollution.
Nonpoint Sources
 Nonpoint sources - are broad, and
diffuse areas, rather than points, from
which pollutants enter bodies of surface
water or air.
 Examples: runoff of chemicals and
sediments from cropland, livestock
feedlots, logged forests, urban streets,
parking lots, lawns, golf courses
 Difficult and expensive to identify and
control such discharges, so not much
progress has been made.
Effects of Water Pollution
 Exposure to infectious disease organisms (pathogens)
mostly through contaminated drinking water.
 3.2 million people die prematurely each year as a
result of contaminated drinking water.
 An average of 8,700 premature deaths a day.
20-2
What are the Major Water
Pollution Problems in Streams
and Lakes?
Water Pollution Problems in Streams
Streams can cleanse themselves if
we do not overload them:
 Undergo a natural recovery process
 Can remove biodegradable wastes, but not slowly
degradable and non-degradable pollutants
 The breakdown of biodegradable wastes by bacteria
depletes dissolved oxygen and creates an oxygen sag
curve
Ohio’s Cuyahoga River
 Water pollution control laws enacted in the 1970s
have greatly increased the number and quality of
waste water treatment plants in the United States
and most other developed countries.
 Extremely polluted with flammable chemicals.
 Prompted by a highly publicized photo of the
burning river in 1969, elected officials enacted laws
that limited the discharge of industrial wastes into
the river and into local sewage systems and
provided funds to upgrade sewage treatment
facilities.
 Today, river is cleaner, no longer flammable, and
highly used by boaters and anglers.
 Successful use of bottom-up pressure by citizens.
India’s Ganges River
 Viewed as a holy river.
 Each day, large numbers of Hindus
bathe, drink from, or take a dip in the
river for religious reasons.
 Highly polluted, yet 350 million people
live in the Ganges River Basin.
 Hindus believe in cremating the dead to
free the soul and throwing the ashes
into the river.
 Indian government plans to build waste
treatment plants to ease pollution.
Water Pollution Problems in Lakes
 Generally less effective at diluting
pollutants than streams are because:
 Often contain stratified layers that undergo little vertical
mixing
 Have little or no flow
 Very vulnerable to contamination by
runoff
 Contaminants can kill bottom life and
fish and birds that feed on
contaminated aquatic organisms.
Cultural Eutrophication
 Cultural eutrophication - over nourishment
of aquatic ecosystems with plant nutrients
(mostly nitrates and phosphates) because of
human activities such as agriculture,
urbanization, and discharges from industrial
plants and sewage treatment plants.
 Produces dense growths or blooms of
organisms like algae and cyanobacteria
during hot weather or drought.
 Reduce lake productivity.
 85% of the large lakes near major U.S.
population centers have some degree of
cultural eutrophication.
Prevention and Reduction of Cultural
Eutrophication
 Luckily, lakes can usually recover from
cultural eutrophication.
 Use advanced (and expensive) waste
treatment to remove nitrates and
phosphates before wastewater enters lakes.
 Mechanically remove excess weeds.
 Control undesirable plant growth with
herbicides and algicides.
 Pump air through lakes and reservoirs to
prevent oxygen depletion.
20-3
What are the Major Pollution
Problems Affecting
Groundwater and Other
Drinking Water Sources?
Major Pollution Problems Affecting
Groundwater
 Common pollutants can seep into groundwater from numerous
sources.
 Contaminates are not diluted and dispersed effectively.
 Much lower concentrations of dissolved oxygen and smaller
populations of decomposing bacteria.
 The cold temperatures of groundwater slow down chemical
reactions that decompose wastes.
 Can take decades to thousands of years for contaminated
groundwater to cleanse itself of slowly degradable wastes (like
DDT). On a human time scale, non degradable wastes (like
toxic lead and arsenic) remain in the water permanently.
Protecting Groundwater
 Treating a contaminated aquifer involves
eliminating the source of pollution and
drilling monitoring wells to determine how
far, in what direction, and how fast the
contaminated plume is moving.
 A computer model is used to project future
dispersion of the contaminant in the aquifer.
 Develop and implement a strategy to clean
up the contamination.
 Preventing contamination is the least
expensive and most effective way to protect
groundwater sources
Purifying Drinking Water
 Complex Techniques:
 Is usually stored in a reservoir and treated in a purification plant
in developed countries.
 Countries like Japan are developing plants that process sewer
water into drinking water.
 El Paso, Texas: 40% of drinking water comes from recycling and
purifying waste water.
 Orange Country, California: completed the world’s largest plant
devoted to making sewer water as pure as distilled water
 Simple Techniques:
 Exposing a clear plastic bottle filled with contaminated water to
intense sunlight
 Nanofilters to clean contaminated water
 LifeStraw
Laws Protecting Drinking Water Quality
 U.S. Safe Drinking Water Act of 1974 - requires
the EPA to establish national drinking water
standards, called maximum contaminant levels,
for any pollutants that may have adverse effects
on human health.
 Despite this, the UN estimates that 5.6 million
Americans drink water that does not meet EPA
standards.
 Health scientists call for strengthening the U.S.
Safe Drink Water Act
Is Bottled Water the Answer?
 Between 1976 and 2006, average bottled water
consumption per person in the US increased
from 7.5 liters (2 gallons) to 113 liters (30
gallons) a year.
 About one-fourth of it is ordinary tap water in a
bottle.
 Bacteria or fungi contaminate about 40% of
bottled water.
 Many bottles are thrown away without being
recycled.
 Manufacture of plastic water bottles emits toxic
gases and liquids.
 Greenhouse gases and other air pollutants are
emitted by the fossil fuels burned to make and
to deliver bottled water to suppliers.
20-4
What are the Major Water
Pollution Problems Affecting
Oceans?
Ocean Pollution is growing and
poorly understood
 About 40% world population lives on coasts
 That population will double by 2050
 Ocean pollution has a large effect
 85% of sewage in developing countries is dumped
untreated into oceans
 Cruise ships also dump tons of waste into oceans
 This pollution creates and spreads disease
 Runoffs release nitrates and phosphates into the
water, creating algae blooms
 Algae blooms deplete oxygen and kill ocean
animals
 They also poison seafood, harming humans
Northern Gulf of Mexico
 Collects agricultural
runoff for 31 states
 Has large zone of
depleted oxygen due to
eutriphication
 Many attempts to reduce
size
 All failed, and zone is still
growing
 Scientists fear soon it
will be uninhabitable
Ocean Oil is a Serious Problem
 Oil spills and blowouts spew large amounts of oil into the ocean
 Costly to clean up
 Most oil pollution comes from leaks from urban runoff
 Oil immediately kills many larvae
 Oil stuck of birds causes them to drown
 Recovery from refined oil usually take triple the time as crude
oil
 Oil slicks on beaches can destroy fishing and tourist economies
 Oil spills can be mechanically cleaned up (booms/skimmers),
but only about 15% effective
 Preventing pollution is the most important goal (double hull)
20-5
How Can We Best Deal with
Water Pollution?
We Need to Reduce Surface Water
Pollution from Nonpoint Sources
 Farmers keep soil
vegetated to prevent
erosion
 Use slow release
fertilizer and use buffers
to prevent runoff
 Use manure for fertilizer
 Use less pesticides and
use IPM
Laws can Help Reduce Water
Pollution from Point Sources
 Federal Pollution Control
Act
 Clean Water Act
 Water Quality Act
 Sets standards for
pollutant limits
 EPA : discharge traing
policy
 Buy credits from other
permit holders
 Would require heavy
scrutiny and gradual
lowering of caps
 Neither is currently in
the policy
Success and Failures of Clean Water
Act
 Annual wetland loss
decreased 80% since
1992
 Swimmable US streams
increased from 36 to
60%
 US population served by
sewage treatment
increased from 32 to
74%
 Number of American
getting good water
increased from 79 to
94%
 40% of streams still too
polluted for fishing
 Tens of thousands of gas
tanks are leaking
 Environmentalist want
more preventive policies
 Very costly to keep
testing amounts of water
pollution
Sewage Treatment Reduces Water
Pollution
 25% of US homes use septic
tanks
 Home wastewater is pumped
into the tank
 Soil and bacteria are used to
treat the water
 When the tank fills every few
years, it must be pumped into
a tank truck
 If not maintained, they can
cause sewage to back up and
Sewage treatment plants
 Sewer pipes bring wastewater to plants
 Primary sewage treatment: Physically removes
suspended solids with screens/filters
 Secondary: Biologically removes dissolved wastes
 Tertiary: Uses specialized processes to remove specific
pollutants. Very costly
 Chlorination: removes disease before discharging
 Storm waters can overflow sewer systems and cause
sewage discharge
 Better to have separate pipe networks
We Can Improve Conventional
Sewage Treatment
 Composting Toilet Systems
 Convert human feces into
fertilizer supplement
 Cheap, saves water, and saves
energy
Wetland Based Sewage Treatment
 Series of tanks to purify water
 Algae decompose organic waste
 Plants take up resulting nutrients
 Passes through marsh to filter out more organic waste
 Some plants can remove toxins and kill pathogens
 Flows into aquarium where microorganisms eaten by snails,
which are eaten by larger fish
 Fish can be sold as bait or food
 Water goes into second marsh for more cleansing
 Water can be treated drinkable using UV light
 Water is then discharged
 Costs as much as conventional sewage plant