CHAPTER 20 Water Pollution and Its Prevention © 2011 Pearson Education, Inc.

CHAPTER 20
Water Pollution and
Its Prevention
© 2011 Pearson Education, Inc.
An introduction to water pollution
• The Mississippi River collects water from 40% of the
U.S.
• Delivers it to the Gulf of Mexico, along with fertilizers
and wastes from feedlot animals
• Drained wetlands no longer intercept agricultural
runoff
• In 1974, scientists found that the water and
sediments in the gulf no longer contained oxygen
• This hypoxic (lacking oxygen) zone is growing
• There is a well-documented relationship between
nitrogen and hypoxia
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The 2008 dead zone in the Gulf of
Mexico
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Excess nitrogen leads to oxygen
depletion
• Abundant nitrogen promotes growth of
phytoplankton (photosynthetic microorganisms)
• Zooplankton (microscopic animals) eat phytoplankton
• These dead organisms are eaten by bacteria, which
also consume oxygen
• Dead zones last from May to September
• Until cold weather mixes the water
• The gulf’s $2.8 billion fishery was affected
• Congress passed the 1998 Harmful Algal Bloom and
Hypoxia Research and Control Act
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Fighting the gulf’s hypoxia
• An interagency task force’s 2000 report confirmed
the nitrogen-dead zone relationship
• Options to reduce nitrogen: use less fertilizer and
restore/promote nitrogen and denitrification processes
• An action plan to reduce the size of the hypoxic area
50% by 2015 has not shrunk the area’s size
• The latest action plan recommends 45% reduction in
nitrogen and phosphorus
• But no specific funding is provided
• Coastal dead zones have doubled every decade
since 1960
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Perspectives on water pollution
• Early in the Industrial Revolution chemicals and
sewage were dumped directly into U.S. waterways
• Contaminating drinking water and causing disease
• In the late 1800s, Pasteur and others showed that
sewage-borne bacteria caused infectious diseases
• Cities implemented sewers and toilets
• Receiving waters became cesspools
• Water became unfit for any recreational use
• Health problems were not seen as being caused by
pollution but as the price of progress
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Legislation protecting water
• The Federal Water Pollution Control Act of 1948
• The first federal action regarding water pollution
• Provided technical assistance but nothing else
• Waterways became open chemical and waste
sewers
• In 1969, Ohio’s Cuyahoga River actually caught fire
• The Clean Water Act of 1972 (CWA)
• Passed by Congress in response to public outrage
about polluted water
• Charged the EPA with restoring and maintaining the
chemical, physical, and biological integrity of waters
• One of the most effective environmental laws enacted
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Cuyahoga River on fire
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Water pollution: sources and types
• Point-source pollution: easy to identify, monitor, and
regulate
• Factories, sewage systems, power plants,
underground coal mines, oil wells
• Nonpoint-source pollution: poorly defined and
scattered
• Agricultural runoff, storm-water runoff (streets, parking
lots, lawns), atmospheric deposition
• Strategies to control water pollution
• Reduce/remove the source: best for nonpoint sources
• Treat the water before release: best for point sources
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Point and nonpoint sources
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Pathogens
• Pathogens: disease-carrying bacteria, viruses,
parasites
• Found in human and animal excrement
• Even after symptoms disappear the organism can still
carry the disease
• Public-health measures prevent diseases
• Purification and disinfection of public water supplies
• Sanitary collection and treatment of wastes
• Sanitary standards where food is prepared for the
public
• Personal and domestic hygiene practices
• Public-health departments set and enforce standards
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The Ganges River in India
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Sanitation = good medicine
• Good health is mostly a result of prevention of
disease through public-health measures
• One billion lack clean drinking water
• 2.5 billion have poor or no sewage treatment
• 2 million/year die from waterborne diseases
• The Millennium Development Goal 7 is to halve, by
2015, proportion of people without clean water or
sanitation
• The world is on track for water, but not sanitation
• Many poor are chronically infected with diseases
• Each year, hundreds die from cholera
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Worldwide distribution of improved
sanitation
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Organic wastes
• Organic matter: human and animal wastes
• Leaves, grass, trash, etc.
• Most (except plastic and some synthetic chemicals) is
biodegradable
• Bacteria and detritus feeders consume organic matter
and oxygen
• Water holds much less dissolved oxygen (DO) than
air
• Cold water holds more DO (10 ppm)
• Even a little organic matter can deplete water’s DO
• Bacteria consuming organic matter keep the DO low
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Biochemical oxygen demand (BOD)
• BOD: a measure of the amount of organic material in
water
• How much oxygen is needed to break matter down
• The higher the BOD, the greater the likelihood DO
will be depleted
• A high BOD limits or precludes animal life
• A DO < 2 or 3 ppm kills fish and shellfish
• Only bacteria can live in anaerobic (no oxygen)
conditions
• A BOD value for raw sewage = 220 ppm
• Even 10 ppm can deplete water of DO
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The oxygen sag curve
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Chemical pollutants
• Inorganic chemicals: heavy metals (lead, mercury,
arsenic, nickel), acids from mine drainage or
precipitation
• Road salts used to melt ice and snow
• Organic chemicals: petroleum, pesticides
• Industrial chemicals: polychlorinated biphenyls
(PCBs), cleaning solvents, detergents
• Many chemicals are toxic at very low levels
• Biomagnification: chemicals become concentrated
when going up the food chain
• Higher concentrations change water chemistry
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Acid mine drainage
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Sediments
• Land weathering and storms wash sediments into
water
• Erosion from farms, deforestation, overgrazing,
construction, mining, roads increases sedimentation
• Clear water supports complex food webs
• Organisms attach to rocks or hide behind them to
prevent washing downstream
• Clay and humus make water muddy
• Reducing light penetration and photosynthesis
• Settled material coats everything, reducing
photosynthesis
• Smothering gills, feeding structures, and eggs
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Stream ecosystem with low bed load
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Bed load
• Bed load: destructive sand and silt that is not
suspended, but is washed along the bottom
• Rolling particles scour organisms from rocks
• Smothering bottom life
• Filling in hiding places
• Plants can’t become established on the shifting sand
• Storm-water management reduces bed load with
drains
• Some housing developments have ponds to trap
runoff
• Water infiltrates the soil, creating wetlands
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Impact of sediment on streams and
rivers
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Storm-water management
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Nutrients
• Nutrients: inorganic materials that are essential for
plants
• Phosphorus and nitrogen: the two most important
nutrients
• Limiting factors if they are in short supply
• Nutrients become pollutants when they stimulate
undesirable plant growth in water
• Point sources: untreated or poorly treated sewage
outfalls
• Particularly in developing countries
• Nonpoint sources: agriculture (fertilizers, manure,
crops, irrigation water), lawns/gardens, golf courses,
drains
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Water quality standards
• Many pollutants are in water only because of
humans
• Pesticides, solvents, detergents
• Others occur naturally and become a problem under
certain conditions
• Nutrients, sediments
• Pollution: any quantity that is harmful to human
health or the environment
• It prevents full use of the environment
• The concentration, not presence, of a substance is
the concern
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Criteria pollutants
• National Recommended Water Quality Criteria
• Provides standards for assessing pollution
• Criteria pollutants: the EPA’s list of 167 substances
• Toxins, nutrients, hardness, pH
• Identifies and recommends concentrations for all
water
• Criteria maximum concentration (CMC): the highest
single concentration beyond which impacts occur
• Criterion continuous concentration (CCC): highest
sustained concentration beyond which impacts occur
• States used these criteria to uphold pollution laws
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Drinking water standards
• These standards are stricter
• Drinking Water Standards and Health Advisories: the
EPA’s table of standards for 94 contaminants
• Enforceable under the Safe Drinking Act (SDWA)
• Presented as maximum contaminant levels (MCLs)
• Arsenic: a known human carcinogen occurring
naturally in groundwater
• Drinking water’s MCL was 50 μg/L (1 μg/L = 1 ppb)
• Scientists warned this was much too high
• After political delays, the EPA lowered it to 10 μg/L
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Other applications of water quality
criteria
• National Pollution Discharge Elimination System
(NPDES): addresses point-source pollution
• Permits for regulating wastewater and industrial
discharges
• Total Maximum Daily Load (TMDL) program: evaluates all
sources (mainly nonpoint) of water pollutants
• Accounts for the water’s ability to assimilate the pollutant
• 92% of U.S. people’s drinking water meets drinking
water standards
• 42,000 rivers, lakes do not meet water quality standards
• Over 60% of U.S. waters have not been assessed at all
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Wastewater treatment and management
• Facilities were built to treat sewage-polluted water
• 1900: the first U.S. wastewater treatment plants were
built
• Heavy rains overflowed the plants and carried raw
sewage to waterways
• Regulations require installation of two systems
• Storm drains: collect and drain precipitation runoff
• Sanitary sewers: receive and treat wastewater (sinks,
tubs, toilets) from homes and buildings
• Through the 1970s many areas still had untreated
wastes
• Increasing pollution drove passage of the CWA
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Pollutants in raw wastewater
• Raw wastewater comes from toilets and all other
drains
• A sewer system brings all wastewater together
• Raw sewage (wastewater): total mixture collected
from all drains
• 99.9% water, 0.1% waste
• 150–200 gallons/person/day
• 10,000 people produce 1.5–2 million gallons/day
• With the addition of storm water, raw wastewater is
diluted even more
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Types of pollutants in wastewater
• Debris and grit: rags, plastic, sand, gravel
• Flushed down toilets or in storm drains
• Particulate organic matter: fecal matter, food wastes,
toilet paper
• Settle out in still water
• Colloidal and dissolved organic matter: fine particles
of organic material, bacteria, urine, soaps,
detergents
• Dissolved inorganic material: nitrogen, phosphorus
and other nutrients from wastes and detergents
• Also, pesticides, heavy metals, other toxic
compounds
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Removing pollutants from wastewater
• Technology for treating wastewater must do the job
at a reasonable cost
• Primary treatment: removes debris and grit
• Bar screen: mechanically rakes debris for removal
and incineration
• Grit chamber: grit is allowed to settle and is removed
• Primary clarifiers: tanks where particulate matter
settles to the bottom and fatty/oily materials float
• Raw sludge: particulates and oily materials that must
be treated separately
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A diagram of wastewater treatment
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Secondary (biological) treatment
• Organisms feed on colloidal and dissolved organic
matter
• Decomposers and detritus feeders
• Oxygen is added to enhance respiration and growth
• Trickling filter system: primary treated water is
sprinkled onto a bed of rocks 6–8 feet deep
• Bacteria, protozoans, rotifers, worms, etc.
• Activated sludge system: the most common
treatment
• Primary treated water enters a tank with an air
bubbling system or paddles
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The activated sludge system
• Activated sludge: a mixture of detritus-feeding
organisms
• Added to water as it enters the tank
• Organisms reduce the biomass (including pathogens)
• Floc: clumps of organisms that settle in still water
• Secondary clarifier tank: organisms settle out
• 90% of organic material has been removed
• Settled organisms (activated sludge) are pumped
back into the aeration tank
• Excess activated sludge is added to the raw sludge
• Organisms oxidize material to CO2, H2O, nutrients
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Trickling filters for secondary treatment
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Biological nutrient removal (BNR)
• BNR: a secondary activated-sludge system
• Removes nutrients and oxidizes detritus
• Nitrogen removal: bacteria convert ammonia and
nitrate to non-nutritive nitrogen gas (denitrification)
• The activated sludge system is partitioned into zones
that promote the denitrifying process
• Phosphorus: is taken up and stored by bacteria
• Bacteria are then added to the raw sludge
• Alternatives to BNR: chemical treatments use lime,
ferric chloride, or a polymer to remove phosphorus
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Biological nutrient removal (BNR)
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Final cleansing and disinfection
• Wastewater is disinfected by:
• Chlorine gas: effective, cheap, but dangerous to work
with and harms aquatic life
• Sodium hypochloride (Chlorox): a safer way to add Cl
• Ozone gas: kills microorganisms but must be
generated (costly and energetically expensive)
• Ultraviolet light: kills microorganisms but little else
• Discharged wastewater has low BOD and may
improve water quality
• Many areas still use only primary, or no, treatments
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Treatment of sludge
• Raw sludge: particulate matter that settles out or
floats to the surface during primary treatment
• Includes excesses from activated-sludge and BNR
• A gray, foul-smelling, syrupy liquid, 97% water
• May contain pathogens
• Sludge may be used as organic material
• If it contains no pathogens and no toxic contaminants
• Sludge is converted to organic fertilizer through
anaerobic digestion, composting, and pasteurization
• It does not remove heavy metals or toxins
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Anaerobic digestion
• Bacteria feeding on sludge in the absence of oxygen
• Sludge digesters: large airtight tanks containing raw
sludge where bacteria convert organic matter to
CO2, H2O, methane (biogas—used to heat the
digester)
• Treated sludge: the material left after digestion
• Stable, nutrient-rich humus suspended in water
• Pathogens have been eliminated
• An excellent organic fertilizer for lawns and fields
• Sludge cake: semisolid, rich material after
dewatering
• Easy to store and spread on fields
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Anaerobic sludge digesters
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Dewatering treated sludge
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Composting and pasteurization
• Composting: mixing raw sludge with water-absorbing
material to reduce the water content
• Windrows: long, narrow piles of compost that allow air
to circulate
• Bacteria and other decomposers break down material
into rich humuslike material for treating poor soil
• Pasteurization: dewatered raw sludge is dried in
ovens
• Kills pathogens
• The dry, odorless pellets are sold as organic fertilizer
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Alternative treatment systems
• Many homes use on-site treatment systems
• The septic tank and leaching field: the most common
and traditional system
• Wastewater flows into tanks where particulates settle
and are digested by bacteria
• Accumulations are periodically pumped out
• Water, organic material, and dissolved nutrients flow
into a leaching field and percolate into the soil
• Soil bacteria decompose the matter
• Gardens can be planted over leaching fields
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Septic tank treatment
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On-site systems frequently fail
• Sewage enters homes, groundwater, and surface
water
• Homeowners don’t know how the systems work
• They aren’t held accountable for pollution
• The EPA provides guidelines, manuals, and
information on proper management
• Successful septic system maintenance includes:
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Not dumping products that kill bacteria or clog the tank
Inspecting and pumping the system regularly
Not using the garbage disposal
Keeping vehicles and equipment off the leaching fields
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Composting toilet systems
• A valuable and inexpensive alternative to septic
systems
• A sanitary means of treating human waste
• Produces a stable, humuslike product
• A toilet connects to a composting reactor that is under
the toilet seat, in basement, or on the ground outside
• An exhaust system (fan) removes odors
• Ventilation promotes aerobic decomposition
• The end product must be legally removed
• These systems need active management
• Reduces toilet wastes by 70%–90%
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Composting toilet system
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Using effluents for irrigation
• Nutrient-rich water from secondary treatment is
beneficial for growing plants
• Keep it out of waterways, but use it on fields
• Effluents must not contain toxic materials
• Cities irrigate open space, lawns, golf courses with
effluent
• Money from selling the water offsets operating costs
• Developing countries use untreated sewage to
irrigate crops
• Growing crops but spreading disease
• Only treated effluents should be used
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Reconstructed wetland systems
• The nutrient-absorbing capacity of wetlands can be
used to treat wastewater
• As part of a recovery program or construction of
artificial wetlands
• The Orlando Easterly Wetlands Reclamation Project
converted 1,200 acres of pastureland back into
wetlands
• After 30 days, the near-pure water enters the
St. Johns River
• The key to success: ensure that these systems are
kept in balance
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Eutrophication
• Introduction of pollutants has greatly increased the
scope and speed of eutrophication
• Benthic plants: aquatic plants that grow attached to,
or are rooted in, the bottom of the body of water
• Aquarium plants, sea grasses
• Submerged aquatic vegetation (SAV): grows under
water by absorbing nutrients from roots in the
sediment
• Needs clear water for light penetration
• Emergent vegetation: the lower parts grow in water
• Their upper parts emerge from the water
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SAV vs. phytoplankton
• Turbid (cloudy) water decreases photosynthesis and
the depth that SAV can survive
• Nutrient enrichment stimulates phytoplankton growth
• Phytoplankton: photosynthetic algae, protists,
cyanobacteria (bacteria containing chlorophyll)
• Grow as single cells or in clumps
• Live suspended in water or floating on the surface
• High nutrient levels encourage phytoplankton
• Growth makes water turbid, which shades out SAV
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Aquatic photosynthesizers
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The impacts of nutrient enrichment
• An oligotrophic lake: light penetrates deeply
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The bottom is visible
Watershed holds its nutrients, so little enters the lake
Low nutrient levels support growth of SAV
Benthic plants support a diverse aquatic ecosystem
High aesthetic, recreational, and fishing qualities
• The process of eutrophication: nutrient enrichment
allows rapid growth of phytoplankton
• Water turbidity increases and shades out SAV
• Dead SAV decreases food, habitat, dissolved oxygen
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Increased phytoplankton
• Phytoplankton biomass can double every 24 hours
• Soon reaches a maximum population density
• Dead phytoplankton settle out, depositing detritus on
the bottom
• Decomposers (bacteria) consume oxygen
• Oxygen depletion leads to suffocation of organisms
and creation of dead zones
• Eutrophication also makes water unappealing for
swimming, drinking, boating, and fishing
• Some phytoplankton secrete toxins that kill
organisms
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Eutrophication
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Shallow lakes and ponds
• In lakes and ponds less than 6–8 feet deep, SAV
can reach the surface, totally covering the water
body with a thick mat of vegetation
• Boating, fishing, swimming are impossible
• Dead mats sink and create a BOD that depletes the
dissolved oxygen
• Killing all organisms, except for bacteria
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Eutrophication in shallow lakes and
ponds
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Natural vs. cultural eutrophication
• Natural eutrophication: part of the process of natural
succession
• Cultural eutrophication: accelerated eutrophication
caused by humans
• Poor farming, urban runoff, sewage
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Combating eutrophication: attacking
the symptoms
• Appropriate where immediate remediation is the goal
and costs are not prohibitive
• All of these methods are temporary
• They have to be repeated often and at significant cost
• Applying herbicides: to control phytoplankton and
SAV
• Herbicides also kill fish and aquatic animals
• Rotting vegetation depletes oxygen, killing more fish
• Vegetation rapidly regrows
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Combating eutrophication: attacking
the symptoms
• Aerating: plastic tubes with tiny holes dissolve
bubbles in the water
• A costly way to break down detritus
• Harvesting: bottom-rooted plants in shallow lakes or
ponds reach and sprawl over the surface
• Plants are removed mechanically or by hand
• The plants make good fertilizer and mulch
• Since roots are left, vegetation soon grows back
• Drawing water down: kills most rooted plants
• But they grow back
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Combating eutrophication: getting at
the root cause
• Long-term strategies to reduce nutrients and
sediments
• Identify the source
• Develop and implement strategies for correction
• Each watershed must be separately analyzed
• The concept of limiting factors: the lack of one
nutrient can suppress growth
• Phosphorus (phosphate): in freshwaters
• Nitrogen (nitrate, ammonium ion): in marine systems
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Ecoregional nutrient criteria
• Since 2001, the EPA has published water-quality
nutrient criteria to prevent and reduce eutrophication
• It lists recommended criteria for:
• Causative factors: nitrogen and phosphorus
• Response factors: chlorophyll a as a measure of
phytoplankton density and water clarity
• Ecoregions have different criteria levels
• States use the criteria as targets as they address
water pollution and eutrophication
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NPDES: control strategy for point
sources
• In heavily populated areas, discharge from sewagetreatment plants is the major source of nutrients
• Along with phosphates in detergents (now banned)
• Phosphates still occur in dishwashing detergents,
though
• It is easier to improve waterways polluted by point
sources
• The NPDES permitting process is the regulatory tool
for reducing point-source pollution
• Anyone discharging pollutants must obtain an
NPDES permit from the EPA or authorized state
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TMDL: control strategy for nonpoint
sources
• The CWA requires states to develop management
programs for nonpoint sources
• The EPA developed regulations via the TMDL
program
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Identify pollutants and estimate their sources
Estimate the water’s ability to assimilate the pollutants
Determine the maximum allowable pollution load
Allocate this level among the sources
• States are responsible for administering TMDL
abatement
• Options include programs, assistance, education
• The EPA oversees and approves the results
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Best management practices
• Reducing or eliminating nonpoint-source pollution
requires different strategies for different sources
• Best management practices: all practices that can
be used to minimize problems
• Once control measures are in place, the water is
monitored to see if standards are met
• If standards are met, the water body is removed
from the list of impaired waters (the record is not
impressive)
• If not, the TMDL process is revisited and new
allowances are allocated
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Recovery
• Water pollution can be controlled and often reversed
• A total watershed management approach is needed
• The Chesapeake Bay’s heavy nutrient pollution
killed 90% of its vital sea grasses
• A 10-month dead zone appears each year
• The 2010 goal of achieving federal clean water
standards will not be met
• New developments add sediments and nutrients too
fast
• A baywide TMDL that will limit nutrient inflows will give
states targets for restoration
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Lake Washington
• A remarkable success story
• A 34-square-mile lake east of Seattle
• During the 1940s and 1950s, sewage treatment plants
dumped 20 million gallons/day of treated water into it
• Unpleasant “blooms” of noxious blue-green algae
grew
• Water lost clarity, fish died, dead algae accumulated
• Concerned citizens diverted the effluent into Puget
Sound
• By 1975, recovery was complete
• Phosphate, the culprit, was drastically reduced
• Citizens are now protecting many other lakes
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Lake Washington
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Public policy and water pollution
• The EPA has the responsibility of overseeing U.S.
waters
• But it can develop regulations only if Congress gives it
the authority
• The Clean Water Act of 1972 (CWA): gives the EPA
jurisdiction over (and requires permits for) all point
sources of pollution
• $78 billion helps cities and towns build treatment
plants
• The Clean Water State Revolving Fund (SRF):
provides direct grants to build treatment facilities
• Money paid back goes as loans to others
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Reauthorization
• Reauthorization of the CWA is long overdue
• Congress is debating:
• Whether the act should be strengthened or weakened
• If regulations intrude on private property rights
• How regulatory relief should be given to industries,
cities, and people
• How to deal with the TMDL program
• For the past 20 years, Congress has reauthorized
the CWA’s provisions and kept the status quo
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Problems still remain
• Nonpoint-source pollution: the U.S.’s major water
pollution problem
• Construction of new wastewater facilities, storm-water
discharge, sewer overflows, wetlands protection, etc.
• Much still remains to be done: too many U.S. water
bodies do not meet water quality standards
• 57% of major facilities pollute above permitted levels
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Progress has been made
• The CWA is one of the most successful
environmental laws
• 208 million have adequate sewage-treatment plants
• Soil erosion has been reduced by 1 billion tons/year
• Two-thirds of the nation’s waterways are safe for
fishing and swimming
• Heavily used rivers, lakes, and bays have been
restored
• Toxic levels in the Great Lakes are reduced
• Public policy and billions of dollars have cleaned
waters
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CHAPTER 20
Water Pollution and
Its Prevention
Active Lecture Questions
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Review Question-1
Point sources of pollution can include all of the
following except
a. factories.
b. coal mines.
c. storm water drainage.
d. power plants.
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Review Question-1 Answer
Point sources of pollution can include all of the
following except
a. factories.
b. coal mines.
c. storm water drainage.
d. power plants.
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Review Question-2
The ______ is a measure of the amount of
organic material in water stated in terms of how
much oxygen will be required to break it down
biologically, chemically, or both.
a. biochemical oxygen demand
b. pathogenic determinant
c. millipore quotient
d. infectious agent report
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Review Question-2 Answer
The ______ is a measure of the amount of
organic material in water stated in terms of how
much oxygen will be required to break it down
biologically, chemically, or both.
a. biochemical oxygen demand
b. pathogenic determinant
c. millipore quotient
d. infectious agent report
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Review Question-3
The two most important nutrient elements for
aquatic plant growth are
a. phosphorus and plutonium.
b. phosphorus and nitrogen.
c. nitrogen and carbon.
d. carbon and helium.
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Review Question-3 Answer
The two most important nutrient elements for
aquatic plant growth are
a. phosphorus and plutonium.
b. phosphorus and nitrogen.
c. nitrogen and carbon.
d. carbon and helium.
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Review Question-4
______ use(s) natural decomposers and
detritus feeders to break down waste.
a. Primary treatment
b. Raw sludge
c. Biological treatment
d. Grit chambers
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Review Question-4 Answer
______ use(s) natural decomposers and
detritus feeders to break down waste.
a. Primary treatment
b. Raw sludge
c. Biological treatment
d. Grit chambers
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Review Question-5
______ refers to a series of events beginning
with nutrient pollution and ending with the
depletion of dissolved oxygen in a water body
and the suffocation of higher organisms.
a. Sewage treatment
b. Phytoplankton removal
c. Oligotrophication
d. Eutrophication
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Review Question-5 Answer
______ refers to a series of events beginning
with nutrient pollution and ending with the
depletion of dissolved oxygen in a water body
and the suffocation of higher organisms.
a. Sewage treatment
b. Phytoplankton removal
c. Oligotrophication
d. Eutrophication
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Interpreting Graphs and Data-1
According to Fig. 20-5, what percentage of the
population of the United States is using
improved sanitation procedures?
a. Less than 50%
b. 60-75%
c. 75-90%
d. 90-100%
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Interpreting Graphs and Data-1 Answer
According to Fig. 20-5, what percentage of the
population of the United States is using
improved sanitation procedures?
a. Less than 50%
b. 60-75%
c. 75-90%
d. 90-100%
© 2011 Pearson Education, Inc.
Interpreting Graphs and Data-2
According to Fig. 20-6, the oxygen sag occurs
in a system when
a. the water is in a
recovery stage.
b. the water is clean.
c. sewage is discharged
with a high BOD.
d. all of the above.
© 2011 Pearson Education, Inc.
Interpreting Graphs and Data-2 Answer
According to Fig. 20-6, the oxygen sag occurs
in a system when
a. the water is in a
recovery stage.
b. the water is clean.
c. sewage is discharged
with a high BOD.
d. all of the above.
© 2011 Pearson Education, Inc.
Thinking Environmentally-1
All of the following are ways to handle sewage
in the absence of municipal collection systems
except
a. septic tank treatment.
b. clarification and disinfection.
c. composting toilet systems.
d. All of these are alternatives to municipal
systems.
© 2011 Pearson Education, Inc.
Thinking Environmentally-1 Answer
All of the following are ways to handle sewage
in the absence of municipal collection systems
except
a. septic tank treatment.
b. clarification and disinfection.
c. composting toilet systems.
d. All of these are alternatives to municipal
systems.
© 2011 Pearson Education, Inc.
Thinking Environmentally-2
Which of the following is the best management
practice for reducing pollution from nonpoint
sources?
a. animal waste management
b. integrated pest management
c. porous pavements
d. all of the above
© 2011 Pearson Education, Inc.
Thinking Environmentally-2 Answer
Which of the following is the best management
practice for reducing pollution from nonpoint
sources?
a. animal waste management
b. integrated pest management
c. porous pavements
d. all of the above
© 2011 Pearson Education, Inc.