Water Pollution

1
Chapter 21

• Water Pollution

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Using Nature to Purify Sewage

• Ecological wastewater purification by a living
  machine.
• Uses the sun and a series of tanks containing
  plants, snails, zooplankton, crayfish, and fish
  (that can be eaten or sold for bait).

Figure 21-1
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WATER POLLUTION SOURCES, TYPES, AND EFFECTS

• Point source specific location (drain pipes,
  ditches, sewer lines)
• Nonpoint source cannot be traced to a single
  site of discharge (atmospheric deposition,
  agricultural / industrial / residential runoff)

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Determining Water Quality

• 1) DO
• 2) BOD
• 3) Fecal coliform - 0/100 ml for drinking water,
  200 colonies/100 ml for swimming
• 4) Chemical analysis
• 5) Indicator species
• 6) Visual analysis

Figure 21-3
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Pollution in Streams

• Oxygen sag curve (5 zones)
• Factors affecting it 1) volume, 2) temp, 3)
  flow rate, 4) pH

Figure 21-4
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POLLUTION IN LAKES

• Dilution of pollutants in lakes is less effective
  due to
• 1) Stratification and little mixing
• 2) Low flow makes them
• susceptible to runoff
• 3) Cultural eutrophication

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POLLUTION OF GROUNDWATER

• It can take hundreds to thousand of years for
  groundwater to cleanse itself of degradable
  wastes.
• Nondegradable wastes (toxic lead, arsenic,
  flouride) are there permanently.
• Slowly degradable wastes (such as DDT) are there
  for decades.
• Groundwater has low flow rates, few bacteria,
  cold temps - all slow down recovery time
• Avg. recycling time for groundwater 1400 years

8

Leaking tank
Aquifer
Bedrock
Water table
Groundwater flow
Free gasoline dissolves in groundwater (dissolved
phase)
Gasoline leakage plume (liquid phase)
Migrating vapor phase
Water well
Contaminant plume moves with the groundwater
Fig. 21-8, p. 502
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Arsenic in Groundwater - a Natural Threat

• Toxic Arsenic (As) can naturally occur at high
  levels in soil and rocks.
• Drilling into aquifers can release As into
  drinking water supplies.
• According to WHO, more than 112 million people
  are drinking water with As levels 5-100 times the
  10 ppb standard
• Causes bladder, lung and skin cancer, and may
  cause kidney and liver cancer.

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OCEAN POLLUTION

• Red tides
• Dead zones (usually about 61/year)

Figure 21-11
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Urban sprawl Bacteria and viruses from sewers and
septic tanks contaminate shellfish beds
Cities Toxic metals and oil from streets and
parking lots pollute waters
Industry Nitrogen oxides from autos
and smokestacks, toxic chemicals, and heavy
metals in effluents flow into bays and estuaries.
Construction sites Sediments are washed
into waterways, choking fish and plants, clouding
waters, and blocking sunlight.
Farms Runoff of pesticides, manure, and
fertilizers adds toxins and excess nitrogen and
phosphorus.
Red tides Excess nitrogen causes explosive growth
of toxicmicroscopic algae, poisoning fish
and marine mammals.
Closed shellfish beds
Closed beach
Oxygen-depleted zone
Toxic sediments Chemicals and toxic metals
contaminate shellfish beds, kill spawning fish,
and accumulate in the tissues of bottom feeders.
Healthy zone Clear, oxygen-rich waters promote
growth of plankton and sea grasses, and support
fish.
Oxygen-depleted zone Sedimentation and
algae overgrowth reduce sunlight, kill beneficial
sea grasses, use up oxygen, and degrade habitat.
Fig. 21-10, p. 505
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Oxygen Depletion in the Northern Gulf of Mexico

• A large zone of oxygen-depleted water forms for
  half of the year in the Gulf of Mexico as a
  result of algae blooms.

Figure 21-A
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The Chesapeake Bay An Estuary in Trouble

• Largest US estuary
• Shallow
• Slow flushing (1)
• High phosphates, nitrates, mercury, lead

Figure 21-12
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OCEAN OIL POLLUTION

• Most ocean oil pollution comes from human
  activities on land.
• It takes about 3 years for many forms of marine
  life to recover from large amounts of crude oil
  (oil directly from ground).
• Recovery from exposure to refined oil (fuel oil,
  gasoline, etc) can take 10-20 years for marine
  life to recover.

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OCEAN POLLUTION CONTRIBUTORS

• Tanker accidents
• Blowouts
• Pipelines
• Offshore wells
• Runoff
• Dredge spoils
• Sludge

Figure 21-13
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WAYS TO PREVENT AND REDUCE SURFACE WATER POLLUTION

• 1) Prevent runoff
• 2) Buffer zone vegetation
• 3) Reduce erosion
• 4) Clean Water Act - increases fishable/swimmable
  lakes, cuts erosion, increases sewage treatment,
  decreases wetland loss
• 5) Water Quality Act - drinking water supplies

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Reducing Water Pollution through Sewage Treatment

• Septic tanks and various levels of sewage
  treatment can reduce point-source water pollution.

Figure 21-15
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Reducing Water Pollution through Sewage Treatment

• Primary sewage treatment a physical process that
  uses screens and a grit tank to remove large
  floating objects and allows settling - removes
  60 of solids
• Secondary sewage treatment a biological process
  in which aerobic bacteria remove as much as 90
  of dissolved and biodegradable, oxygen demanding
  organic wastes.
• http//www.dcwasa.com/about/model_flash.cfm

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Different treatment processes

• Wastewater treatment is divided into three main
  processes.
• Physical processes comprising screening or
  straining, sedimentation, flocculation and
  filtration.
• Chemical treatment using adsorption, coagulation,
  ion exchange, precipitation.
• Biological treatment processes with dispersed
  growth system( activated sludge, stabilization
  ponds) fixed film reactors( biological filters
  such as tricking filter)

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Reducing Water Pollution through Sewage Treatment

• Primary and Secondary sewage treatment.

Figure 21-16
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Reducing Water Pollution through Sewage Treatment

• Advanced or tertiary sewage treatment
• Uses series of chemical and physical processes to
  remove specific pollutants left (especially
  nitrates and phosphates).
• Water is chlorinated to remove coloration and to
  kill disease-carrying bacteria and some viruses
  (disinfect).
• Some areas use natural wetlands.

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Is Bottled Water the Answer?

• Some bottled water is not as pure as tap water
  and costs much more.
• 1.4 million metric tons of plastic bottles are
  thrown away.
• Fossil fuels are used to make plastic bottles.
• The oil used to produce plastic bottles in the
  U.S. each year would fuel 100,000 cars.

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Water Laws

• SDWA 74 - EPA establishes national drinking
  water standards - not on wells
• Water Quality Act 65 - established water quality
  standards for streams
• Ocean Dumping Act 72 - must have permit to
  dispose of materials
• Clean Water Act - federal assistance for sewage
  treatment, permit to discharge, EPA sets
  pollution standards

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Thermal Pollution of Water

• Affects the solubility of oxygen other gases
• If temperature increases, DO decreases