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© 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
© 2011 Pearson Education, Inc. The 2008 dead zone in the Gulf of Mexico
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. Cuyahoga River on fire
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. Point and nonpoint sources
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. The Ganges River in India
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. Worldwide distribution of improved sanitation
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. The oxygen sag curve
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. Acid mine drainage
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. Stream ecosystem with low bed load
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. Impact of sediment on streams and rivers
© 2011 Pearson Education, Inc. Storm-water management
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. A diagram of wastewater treatment
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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 CO 2, H 2 O, nutrients
© 2011 Pearson Education, Inc. Trickling filters for secondary treatment
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. Biological nutrient removal (BNR)
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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 CO 2, H 2 O, 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
© 2011 Pearson Education, Inc. Anaerobic sludge digesters
© 2011 Pearson Education, Inc. Dewatering treated sludge
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. Septic tank treatment
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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%
© 2011 Pearson Education, Inc. Composting toilet system
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. Aquatic photosynthesizers
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. Eutrophication
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. Eutrophication in shallow lakes and ponds
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. Lake Washington
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. CHAPTER 20 Water Pollution and Its Prevention Active Lecture Questions
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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 Answer
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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 Answer
© 2011 Pearson Education, Inc. ______ 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
© 2011 Pearson Education, Inc. ______ 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 Answer
© 2011 Pearson Education, Inc. ______ 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
© 2011 Pearson Education, Inc. ______ 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 Answer
© 2011 Pearson Education, Inc. 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 % Interpreting Graphs and Data-1
© 2011 Pearson Education, Inc. 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 % Interpreting Graphs and Data-1 Answer
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
© 2011 Pearson Education, Inc. 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
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