Chapter 20 Water Pollution

The Seattle, Washington Area, U.S. Figure 20.1: The U.S. city of Seattle, Washington, was founded on the shore of Puget Sound and quickly expanded eastward toward Lake Washington. Fig. 20-1, p. 528

Core Case Study: Lake Washington Sewage dumped into Lake Washington 1955: Edmondson discovered cyanobacteria in the lake Role of phosphorus Public pressure led to cleanup of the lake Sewage treatment plant effluent to Puget Sound New pollution challenges

Kayaker Enjoys Lake Washington Figure 20.2: With the city of Seattle in the background, this kayaker enjoys the waters of Lake Washington. The once badly polluted lake has recovered, but population pressures and the resulting wastes are threatening it again. Fig. 20-2, p. 528

20-1 What Are the Causes and Effects of Water Pollution? Concept 20-1A Water pollution causes illness and death in humans and other species, and disrupts ecosystems. Concept 20-1B The chief sources of water pollution are agricultural activities, industrial facilities, and mining, but growth in population and resource use make it increasingly worse.

Water Pollution Comes from Point and Nonpoint Sources (1) Change in water quality that can harm organisms or make water unfit for human uses Contamination with chemicals Excessive heat Point sources Located at specific places Easy to identify, monitor, and regulate Examples

Water Pollution Comes from Point and Nonpoint Sources (2) Broad, diffuse areas Difficult to identify and control Expensive to clean up Examples

Water Pollution Comes from Point and Nonpoint Sources (3) Leading causes of water pollution Agriculture activities Sediment eroded from the lands Fertilizers and pesticides Bacteria from livestock and food processing wastes Industrial facilities Mining

Point Source of Polluted Water in Gargas, France Figure 20.3: This point-source water pollution flows uncontrolled into a stream near Gargas, France. Fig. 20-3, p. 530

Nonpoint Sediment from Unprotected Farmland Flows into Streams Figure 20.4: Nonpoint sediment pollution eroded from farmland flows into streams and sometimes changes their courses or dams them up. As measured by weight, it is the largest source of water pollution. Question: What do you think the owner of this farm could have done to prevent such sediment pollution? Fig. 20-4, p. 530

Lake Polluted with Mining Wastes Figure 20.5: The water in this lake is polluted with mining wastes. Fig. 20-5, p. 531

Plastic Wastes in Mountain Lake Figure 20.6: Plastics and other forms of waste pollute this mountain lake as well as many bodies of water around the world, and can release harmful chemicals into the water. Fig. 20-6, p. 531

Major Water Pollutants Have Harmful Effects Infectious disease organisms: contaminated drinking water The World Health Organization (WHO) 1.6 million people die every year, mostly under the age of 5

Major Water Pollutants and Their Sources Table 20-1 Table 20-1, p. 532

Common Diseases Transmitted to Humans through Contaminated Drinking Water Table 20-2 Table 20-2, p. 532

Science Focus: Testing Water for Pollutants (1) Variety of tests to determine water quality Coliform bacteria: Escherichia coli, significant levels Level of dissolved oxygen (DO) Chemical analysis

Science Focus: Testing Water for Pollutants (2) Indicator species Examples Bacteria and yeast glow in the presence of a particular toxic chemical Color and turbidity of the water

Water Quality as Measured by Dissolved Oxygen Content in Parts per Million Figure 20.A: Scientists measure dissolved oxygen (DO) content in parts per million (ppm) at 20°C (68°F) as an indicator of water quality. Only a few fish species can survive in water with less than 4 ppm of dissolved oxygen at this temperature. Some warm-water species have evolved ways to tolerate low DO levels better than most cold-water species can. Question: Would you expect the dissolved oxygen content of polluted water to increase or decrease if the water is heated? Explain. Fig. 20-A, p. 533

Water Quality DO (ppm) at 20°C 8–9 Good Slightly polluted 6.7–8 Moderately polluted 4.5–6.7 Heavily polluted Figure 20.A: Scientists measure dissolved oxygen (DO) content in parts per million (ppm) at 20°C (68°F) as an indicator of water quality. Only a few fish species can survive in water with less than 4 ppm of dissolved oxygen at this temperature. Some warm-water species have evolved ways to tolerate low DO levels better than most cold-water species can. Question: Would you expect the dissolved oxygen content of polluted water to increase or decrease if the water is heated? Explain. 4–4.5 Gravely polluted Below 4 Fig. 20-A, p. 533

20-2 What Are the Major Water Pollution Problems in Streams and Lakes? Concept 20-2A Streams and rivers around the world are extensively polluted, but they can cleanse themselves of many pollutants if we do not overload them or reduce their flows. Concept 20-2B The addition of excessive nutrients to lakes from human activities can disrupt their ecosystems, and prevention of such pollution is more effective and less costly than cleaning it up.

Streams Can Cleanse Themselves If We Do Not Overload Them Dilution Biodegradation of wastes by bacteria takes time Oxygen sag curve

Dilution and Decay of Degradable, Oxygen-Demanding Wastes in a Stream Figure 20.7: Natural capital. A stream can dilute and decay degradable, oxygen-demanding wastes, and it can also dilute heated water. This figure shows the oxygen sag curve (blue) and the curve of oxygen demand (red). Depending on flow rates and the amount of biodegradable pollutants, streams recover from oxygen-demanding wastes and from the injection of heated water if they are given enough time and are not overloaded (Concept 20-2a). See an animation based on this figure at CengageNOW™. Question: What would be the effect of putting another discharge pipe emitting biodegradable waste to the right of the one in this picture? Fig. 20-7, p. 534

Point source Normal clean water organisms (Trout, perch, bass, mayfly, stonefly) Pollution- tolerant fishes (carp, gar) Fish absent, fungi, sludge worms, bacteria (anaerobic) Pollution- tolerant fishes (carp, gar) Normal clean water organisms (Trout, perch, bass, mayfly, stonefly) 8 ppm Types of organisms Dissolved oxygen (ppm) 8 ppm Figure 20.7: Natural capital. A stream can dilute and decay degradable, oxygen-demanding wastes, and it can also dilute heated water. This figure shows the oxygen sag curve (blue) and the curve of oxygen demand (red). Depending on flow rates and the amount of biodegradable pollutants, streams recover from oxygen-demanding wastes and from the injection of heated water if they are given enough time and are not overloaded (Concept 20-2a). See an animation based on this figure at CengageNOW™. Question: What would be the effect of putting another discharge pipe emitting biodegradable waste to the right of the one in this picture? Biochemical oxygen demand Clean Zone Recovery Zone Septic Zone Decomposition Zone Clean Zone Fig. 20-7, p. 534

Stream Pollution in More Developed Countries 1970s: Water pollution control laws Successful water clean-up stories Ohio Cuyahoga River, U.S. Thames River, Great Britain Contamination of toxic inorganic and organic chemicals by industries and mines

Individuals Matter: The Man Who Planted Trees to Restore a Stream John Beal: restoration of Hamm Creek, Seattle, WA, U.S. Planted trees Persuaded companies to stop dumping Removed garbage

Global Outlook: Stream Pollution in Developing Countries Half of the world’s 500 major rivers are polluted Untreated sewage Industrial waste India’s rivers China’s rivers

Natural Capital Degradation: Highly Polluted River in China Figure 20.8: Natural capital degradation. This highly polluted river in central China has been turned greenish-black by uncontrolled pollution from thousands of factories. In some parts of China, river water is too toxic to touch, much less drink. The cleanup and modernization of Chinese cities such as Beijing and Shanghai are forcing polluting refineries and factories to move to rural areas where two-thirds of China’s population resides. Liver and stomach cancers, linked in some cases to water pollution, are among the leading causes of death in the countryside. Farmers too poor to buy bottled water must often drink polluted well water. Fig. 20-8, p. 535

Trash Truck Disposing of Garbage into a River in Peru Figure 20.9: Global outlook: This garbage truck is dumping trash into a river in Peru. Fig. 20-9, p. 536

Too Little Mixing and Low Water Flow Makes Lakes Vulnerable to Water Pollution Less effective at diluting pollutants than streams Stratified layers Little vertical mixing Little of no water flow Can take up to 100 years to change the water in a lake Biological magnification of pollutants

Lake Fish Killed by Water Pollution Figure 20.10: Water pollution has killed the fish in this lake. Fig. 20-10, p. 536

Cultural Eutrophication Is Too Much of a Good Thing (1) Natural enrichment of a shallow lake, estuary, or slow-moving stream Caused by runoff into lake that contains nitrates and phosphates Oligotrophic lake Low nutrients, clear water

Cultural Eutrophication Is Too Much of a Good Thing (2) Nitrates and phosphates from human sources Farms, feedlots, streets, parking lots Fertilized lawns, mining sites, sewage plants During hot weather or droughts Algal blooms Increased bacteria More nutrients Anaerobic bacteria

Cultural Eutrophication Is Too Much of a Good Thing (3) Prevent or reduce cultural eutrophication Remove nitrates and phosphates Diversion of lake water Clean up lakes Remove excess weeds Use herbicides and algaecides; down-side? Pump in air

Cultural Eutrophication of Chinese Lake Figure 20.11: Global outlook: Severe cultural eutrophication has covered this lake near the Chinese city of Haozhou with algae. Fig. 20-11, p. 537

Revisiting Lake Washington and Puget Sound Severe water pollution can be reversed Citizen action combined with scientific research Good solutions may not work forever Wastewater treatment plant effluents sent into Puget Sound Now what’s happening?

Case Study: Pollution in the Great Lakes (1) 1960s: Many areas with cultural eutrophication 1972: Canada and the United States: Great Lakes pollution control program Decreased algal blooms Increased dissolved oxygen Increased fishing catches Swimming beaches reopened Better sewage treatment plants Fewer industrial wastes Bans on phosphate-containing household products

Case Study: Pollution in the Great Lakes (2) Problems still exist Raw sewage Nonpoint runoff of pesticides and fertilizers Biological pollution Atmospheric deposition of pesticides and Hg

Case Study: Pollution in the Great Lakes (3) 2007 State of the Great Lakes report New pollutants found Wetland loss and degradation Declining of some native species Native carnivorous fish species declining What should be done?

The Great Lakes of North America Figure 20.12: The five Great Lakes of North America make up the world’s largest freshwater system. Dozens of major cities in the United States and Canada are located on their shores, and water pollution in the lakes is a growing problem. Fig. 20-12, p. 538

20-3 Pollution Problems Affecting Groundwater, Other Water Sources Concept 20-3A Chemicals used in agriculture, industry, transportation, and homes can spill and leak into groundwater and make it undrinkable. Concept 20-3B There are both simple an complex ways to purify groundwater used as a source of drinking water, but protecting it through pollution prevention is the least expensive and most effective strategy.

Ground Water Cannot Cleanse Itself Very Well (1) Source of drinking water Common pollutants Fertilizers and pesticides Gasoline Organic solvents Pollutants dispersed in a widening plume

Ground Water Cannot Cleanse Itself Very Well (2) Slower chemical reactions in groundwater due to Slow flow: contaminants not diluted Less dissolved oxygen Fewer decomposing bacteria Low temperatures

Principal Sources of Groundwater Contamination in the U.S. Figure 20.13: Natural capital degradation. These are the principal sources of groundwater contamination in the United States (Concept 20-3a). Another source in coastal areas is saltwater intrusion from excessive groundwater withdrawal. (Figure is not drawn to scale.) Question: What are three sources shown in this picture that might be affecting groundwater in your area? Fig. 20-13, p. 540

Leakage from faulty casing Polluted air Hazardous waste injection well Pesticides and fertilizers Coal strip mine runoff Deicing road salt Buried gasoline and solvent tanks Cesspool, septic tank Pumping well Gasoline station Water pumping well Waste lagoon Sewer Landfill Accidental spills Leakage from faulty casing Figure 20.13: Natural capital degradation. These are the principal sources of groundwater contamination in the United States (Concept 20-3a). Another source in coastal areas is saltwater intrusion from excessive groundwater withdrawal. (Figure is not drawn to scale.) Question: What are three sources shown in this picture that might be affecting groundwater in your area? Discharge Freshwater aquifer Freshwater aquifer Freshwater aquifer Groundwater flow Fig. 20-13, p. 540

Groundwater Pollution Is a Serious Hidden Threat in Some Areas China: 90% of urban aquifers are contaminated or overexploited U.S.: FDA reports of toxins found in many aquifers Threats Gasoline, oil Nitrate ions Arsenic

Pollution Prevention Is the Only Effective Way to Protect Groundwater Prevent contamination of groundwater Cleanup: expensive and time consuming

Solutions: Groundwater Pollution, Prevention and Cleanup Figure 20.14: There are ways to prevent and ways to clean up contamination of groundwater but prevention is the only effective approach (Concept 20-3B). Questions: Which two of these preventive solutions do you think are the most important? Why? Fig. 20-14, p. 541

Groundwater Pollution Solutions Groundwater Pollution Prevention Cleanup Find substitutes for toxic chemicals Pump to surface, clean, and return to aquifer (very expensive) Keep toxic chemicals out of the environment Install monitoring wells near landfills and underground tanks Inject microorganisms to clean up contamination (less expensive but still costly) Require leak detectors on underground tanks Ban hazardous waste disposal in landfills and injection wells Figure 20.14: There are ways to prevent and ways to clean up contamination of groundwater but prevention is the only effective approach (Concept 20-3B). Questions: Which two of these preventive solutions do you think are the most important? Why? Store harmful liquids in aboveground tanks with leak detection and collection systems Pump nanoparticles of inorganic compounds to remove pollutants (still being developed) Fig. 20-14, p. 541

There Are Many Ways to Purify Drinking Water Reservoirs and purification plants Process sewer water to drinking water Expose clear plastic containers to sunlight (UV) The LifeStraw PUR: chlorine and iron sulfate powder

The LifeStraw: Personal Water Purification Device Figure 20.15: The LifeStraw™, designed by Torben Vestergaard Frandsen, is a personal water purification device that gives many poor people access to safe drinking water. Here, four young men in Uganda demonstrate its use. Question: Do you think the development of such devices should make prevention of water pollution less of a priority? Explain. Fig. 20-15, p. 542

Case Study: Protecting Watersheds Instead of Building Water Purification Plants New York City water Reservoirs in the Catskill Mountains Paid towns, farmers, and others in the watershed to restore forests, wetlands, and streams Saved the cost of building a plant: $6 billion

Using Laws to Protect Drinking Water Quality 1974: U.S. Safe Drinking Water Act Sets maximum contaminant levels for any pollutants that affect human health Health scientists: strengthen the law Water-polluting companies: weaken the law

Case Study: Is Bottled Water the Answer? U.S.: some of the cleanest drinking water Bottled water Some from tap water 40% bacterial contamination Fuel cost to manufacture the plastic bottles Recycling of the plastic 240-10,000x the cost of tap water Growing back-to-the-tap movement

20-4 What Are the Major Water Pollution Problems Affecting Oceans? Concept 20-4A The great majority of ocean pollution originates on land and includes oil and other toxic chemicals as well as solid waste, which threaten fish and wildlife and disrupt marine ecosystems. Concept 20-4B The key to protecting the oceans is to reduce the flow of pollution from land and air and from streams emptying into these waters.

Ocean Pollution Is a Growing and Poorly Understood Problem (1) 2006: State of the Marine Environment 80% of marine pollution originates on land Sewage Coastal areas most affected Deeper ocean waters Dilution Dispersion Degradation

Ocean Pollution Is a Growing and Poorly Understood Problem (2) Cruise line pollution: what is being dumped? U.S. coastal waters Raw sewage Sewage and agricultural runoff: NO3- and PO43- Harmful algal blooms Oxygen-depleted zones Huge mass of plastic in North Pacific Ocean

Residential Areas, Factories, and Farms Contribute to Pollution of Coastal Waters Figure 20.16: Natural capital degradation. Residential areas, factories, and farms all contribute to the pollution of coastal waters. According to the UN Environment Programme, coastal water pollution costs the world more than $30,000 a minute, primarily for health problems and premature deaths. Questions: What do you think are the three worst pollution problems shown here? For each one, how does it affect two or more of the ecological and economic services listed in Figure 8-5 (p. 172)? Fig. 20-16, p. 545

Industry Nitrogen oxides from autos and smokestacks, toxic chemicals, and heavy metals in effluents flow into bays and estuaries. Cities Toxic metals and oil from streets and parking lots pollute waters; sewage adds nitrogen and phosphorus. Urban sprawl Bacteria and viruses from sewers and septic tanks contaminate shellfish beds and close beaches; runoff of fertilizer from lawns adds nitrogen and phosphorus. Construction sites Sediments are washed into waterways, choking fish and plants, clouding waters, and blocking sunlight. Farms Runoff of pesticides, manure, and fertilizers adds toxins and excess nitrogen and phosphorus. Red tides Excess nitrogen causes explosive growth of toxic microscopic algae, poisoning fish and marine mammals. Closed shellfish beds Closed beach Oxygen-depleted zone Figure 20.16: Natural capital degradation. Residential areas, factories, and farms all contribute to the pollution of coastal waters. According to the UN Environment Programme, coastal water pollution costs the world more than $30,000 a minute, primarily for health problems and premature deaths. Questions: What do you think are the three worst pollution problems shown here? For each one, how does it affect two or more of the ecological and economic services listed in Figure 8-5 (p. 172)? Toxic sediments Chemicals and toxic metals contaminate shellfish beds, kill spawning fish, and accumulate in the tissues of bottom feeders. Oxygen-depleted zone Sedimentation and algae overgrowth reduce sunlight, kill beneficial sea grasses, use up oxygen, and degrade habitat. Healthy zone Clear, oxygen-rich waters promote growth of plankton and sea grasses, and support fish. Fig. 20-16, p. 545

Science Focus: Oxygen Depletion in the Northern Gulf Of Mexico Severe cultural eutrophication Oxygen-depleted zone Overfertilized coastal area Preventive measures Will it reach a tipping point?

A Large Zone of Oxygen-Depleted Water in the Gulf of Mexico Due to Algal Blooms Figure 20.B: Natural capital degradation. A large zone of oxygen-depleted water (containing less than 2 ppm dissolved oxygen) forms each year in the Gulf of Mexico (lower right drawing) as a result of oxygen-depleting algal blooms caused primarily by high inputs of plant nutrients from the Mississippi River basin (top). The drawing (bottom left), based on a satellite image, shows how these inputs spread along the coast during the summer of 2008. In the image, reds and greens represent high concentrations of phytoplankton and river sediment. This problem is worsened by loss of wetlands, which would have filtered some of these plant nutrients. Question: Can you think of a product you used today that was directly connected to this sort of pollution? (Data from NASA) Fig. 20-B, p. 546

Mississippi River Basin Missouri River Mississippi River Basin Ohio River Mississippi River MS Figure 20.B: Natural capital degradation. A large zone of oxygen-depleted water (containing less than 2 ppm dissolved oxygen) forms each year in the Gulf of Mexico (lower right drawing) as a result of oxygen-depleting algal blooms caused primarily by high inputs of plant nutrients from the Mississippi River basin (top). The drawing (bottom left), based on a satellite image, shows how these inputs spread along the coast during the summer of 2008. In the image, reds and greens represent high concentrations of phytoplankton and river sediment. This problem is worsened by loss of wetlands, which would have filtered some of these plant nutrients. Question: Can you think of a product you used today that was directly connected to this sort of pollution? (Data from NASA) LA LOUISIANA Mississippi River TX Depleted oxygen Gulf of Mexico Gulf of Mexico Fig. 20-B, p. 546

Missouri River Mississippi River Basin Ohio River Mississippi River Depleted oxygen Stepped Art Fig. 20-B, p. 546

Ocean Pollution from Oil (1) Crude and refined petroleum Highly disruptive pollutants Largest source of ocean oil pollution Urban and industrial runoff from land 1989: Exxon Valdez, oil tanker 2010: BP explosion in the Gulf of Mexico

Ocean Pollution from Oil (2) Volatile organic hydrocarbons Kill many aquatic organisms Tar-like globs on the ocean’s surface Coat animals Heavy oil components sink Affect the bottom dwellers

Ocean Pollution from Oil (3) Faster recovery from crude oil than refined oil Cleanup procedures Methods of preventing oil spills

Solutions: Coastal Water Pollution, Prevention and Cleanup Figure 20.17: There are a number of methods for preventing or cleaning up excessive pollution of coastal waters (Concept 20-4B). Questions: Which two of these solutions do you think are the most important? Why? Fig. 20-17, p. 547

Coastal Water Pollution Solutions Coastal Water Pollution Prevention Cleanup Reduce input of toxic pollutants Improve oil-spill cleanup capabilities Separate sewage and storm water lines Use nanoparticles on sewage and oil spills to dissolve the oil or sewage (still under development) Ban dumping of wastes and sewage by ships in coastal waters Ban dumping of hazardous material Figure 20.17: There are a number of methods for preventing or cleaning up excessive pollution of coastal waters (Concept 20-4B). Questions: Which two of these solutions do you think are the most important? Why? Require secondary treatment of coastal sewage Strictly regulate coastal development, oil drilling, and oil shipping Use wetlands, solar-aquatic, or other methods to treat sewage Require double hulls for oil tankers Fig. 20-17, p. 547

Deepwater Horizon Blowout in the Gulf of Mexico, April 20, 2010 Figure 20.18: On April 20, 2010 oil and natural gas escaping from an oil-well borehole ignited and caused an explosion on the British Petroleum (BP) Deepwater Horizon drilling platform in the Gulf of Mexico. The accident sank the rig and killed 11 of its crewmembers. The ruptured wellhead released massive amounts of crude oil that contaminated ecologically vital coastal marshes (Figure 8-8, p. 174), mangroves (Figure 8-10, p. 175), sea-grass beds (Figure 8-9, p. 174) and deep ocean aquatic life. It also disrupted the livelihoods of people depending on the gulf’s coastal fisheries and caused large economic losses for the gulf’s tourism business. This disaster was caused by a combination of equipment failure, human error, failure by BP to prepare for a major oil release, and inadequate government regulation of oil drilling in the Gulf of Mexico. Fig. 20-18, p. 547

Case Study: The Exxon Valdez Oil Spill 1989: Alaska’s Prince William Sound 41 million liters of crude oil 5200 km of coastline Killed 250,000 seabirds $15 billion in damages to economy Exxon paid $3.8 billion in damages and clean-up costs Led to improvements in oil tanker safety and clean-up strategies

20-5 How Can We Best Deal with Water Pollution? Concept 20-5 Reducing water pollution requires we prevent it, work with nature to treat sewage, cut resource use and waste, reduce poverty, and slow population growth.

Reducing Surface Water Pollution from Nonpoint Sources Agriculture Reduce erosion Reduce the amount of fertilizers Plant buffer zones of vegetation Use organic farming techniques Use pesticides prudently Control runoff Tougher pollution regulations for livestock operations Deal better with animal waste

Laws Can Help Reduce Water Pollution from Point Sources 1972: Clean Water Act 1987: Water Quality Act EPA: experimenting with a discharge trading policy that uses market forces Cap and trade system Could this allow pollutants to build up?

Case Study: The U.S. Experience with Reducing Point-Source Pollution (1) Numerous improvements in water quality Some lakes and streams are not safe for swimming or fishing Treated wastewater still produces algal blooms High levels of Hg, pesticides, and other toxic materials in fish

Case Study: The U.S. Experience with Reducing Point-Source Pollution (2) Leakage of gasoline storage tanks into groundwater Many violations of federal laws and regulations Need to strengthen the Clean Water Act

Sewage Treatment Reduces Water Pollution (1) Septic tank system Wastewater or sewage treatment plants Primary sewage treatment Physical process Secondary sewage treatment Biological process with bacteria Tertiary or advance sewage treatment Special filtering processes Bleaching, chlorination

Sewage Treatment Reduces Water Pollution (2) Many cities violate federal standards for sewage treatment plants Should there be separate pipes for sewage and storm runoff? Health risks of swimming in water with blended sewage wastes

Solutions: Septic Tank System Figure 20.19: Solutions. Septic tank systems are often used for disposal of domestic sewage and wastewater in rural and suburban areas. Fig. 20-19, p. 550

Manhole cover (for cleanout) Septic tank Gas Distribution box Scum Wastewater Sludge Drain field (gravel or crushed stone) Figure 20.19: Solutions. Septic tank systems are often used for disposal of domestic sewage and wastewater in rural and suburban areas. Vent pipe Perforated pipe Fig. 20-19, p. 550

Solutions: Primary and Secondary Sewage Treatment Figure 20.20: Solutions. Primary and secondary sewage treatment systems help to reduce water pollution. Question: What do you think should be done with the sludge produced by sewage treatment plants? Fig. 20-20, p. 551

Chlorine disinfection tank Bar screen Grit chamber Settling tank Primary Secondary Chlorine disinfection tank Bar screen Grit chamber Settling tank Aeration tank Settling tank To river, lake, or ocean Sludge Raw sewage from sewers Activated sludge (kills bacteria) Air pump Figure 20.20: Solutions. Primary and secondary sewage treatment systems help to reduce water pollution. Question: What do you think should be done with the sludge produced by sewage treatment plants? Sludge digester Disposed of in landfill or ocean or applied to cropland, pasture, or rangeland Sludge drying bed Fig. 20-20, p. 551

Sludge digester To river, lake, or ocean Primary Grit chamber Bar screen Settling tank Secondary Chlorine disinfection tank Aeration tank Settling tank Sludge Disposed of in landfill or ocean or applied to cropland, pasture, or rangeland Raw sewage from sewers Sludge digester Sludge drying bed (kills bacteria) To river, lake, or ocean Activated sludge Air pump Stepped Art Fig. 20-20, p. 551

We Can Improve Conventional Sewage Treatment Peter Montague: environmental scientist Remove toxic wastes before water goes to the municipal sewage treatment plants Reduce or eliminate use and waste of toxic chemicals Use composting toilet systems Wetland-based sewage treatment systems

Science Focus: Treating Sewage by Working with Nature John Todd: biologist Natural water purification system Sewer water flows into a passive greenhouse Solar energy and natural processes remove and recycle nutrients Diversity of organisms used

Solutions: Ecological Wastewater Purification by a Living Machine, RI, U.S. Figure 20.C: Solutions. This is an ecological wastewater purification system called a living machine. This Solar Sewage Treatment Plant is in the U.S. city of Providence, Rhode Island. Biologist John Todd is demonstrating this ecological process he invented for purifying wastewater by using the sun and a series of tanks containing living organisms. Todd and others are conducting research to perfect such solar–aquatic sewage treatment systems based on working with nature. Fig. 20-C, p. 553

There Are Sustainable Ways to Reduce and Prevent Water Pollution Developed countries Bottom-up political pressure to pass laws Developing countries Little has been done to reduce water pollution China : ambitious plan

Solutions: Methods for Preventing and Reducing Water Pollution Figure 20.21: There are a number of ways to prevent and reduce water pollution (Concept 20-5). Questions: Which two of these solutions do you think are the most important? Why? Fig. 20-21, p. 553

What Can You Do? Reducing Water Pollution Figure 20.22: Individuals matter. You can help reduce water pollution. Questions: Which three of these actions do you think are the most important? Why? Fig. 20-22, p. 554

Three Big Ideas There are a number of ways to purify drinking water, but the most effective and cheapest strategy is pollution control. The key to protecting the oceans is to reduce the flow of pollution from land and air, and from streams emptying into ocean waters.

Three Big Ideas Reducing water pollution requires that we prevent it, work with nature in treating sewage, cut resource use and waste, reduce poverty, and slow population growth.