© 2011 pearson education, inc. chapter 20 water pollution and its prevention

© 2011 Pearson Education, Inc.

CHAPTER 20

Water Pollution and Its Prevention


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


The 2008 dead zone in the Gulf of Mexico


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


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


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


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


Cuyahoga River on fire


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


Point and nonpoint sources


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


The Ganges River in India


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


Worldwide distribution of improved sanitation


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


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


The oxygen sag curve


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


Acid mine drainage


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


Stream ecosystem with low bed load


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


Impact of sediment on streams and rivers


Storm-water management


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


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


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


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


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


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


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


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


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


A diagram of wastewater treatment


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


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


Trickling filters for secondary treatment


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


Biological nutrient removal (BNR)


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


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


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


Anaerobic sludge digesters


Dewatering treated sludge


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


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


Septic tank treatment


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:• 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


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%


Composting toilet system


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


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


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


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


Aquatic photosynthesizers


The impacts of nutrient enrichment

• An oligotrophic lake: light penetrates deeply• 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


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


Eutrophication


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


Eutrophication in shallow lakes and ponds


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


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


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


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


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


NPDES: control strategy for point sources• In heavily populated areas, discharge from sewage-

treatment 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


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• 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


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


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


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


Lake Washington


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


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


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


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


CHAPTER 20

Water Pollution andIts Prevention

Active Lecture Questions


Point sources of pollution can include all of the following except

a. factories.

b. coal mines.

c. storm water drainage.

d. power plants.

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.

Review Question-1 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

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



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.

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.



______ use(s) natural decomposers and detritus feeders to break down waste.

a. Primary treatment

b. Raw sludge

c. Biological treatment

d. Grit chambers

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



______ 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

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



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%

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%

Interpreting Graphs and Data-1 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.

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.

Interpreting Graphs and Data-2 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.

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.

Thinking Environmentally-1 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

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

Thinking Environmentally-2 Answer

© 2011 pearson education, inc. chapter 20 water pollution and its prevention

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