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Chapter 21

Chapter 21. Water Pollution. POLLUTION OF FRESHWATER STREAMS. Flowing streams can recover from a moderate level of degradable water pollutants if they are not overloaded and their flows are not reduced.

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Chapter 21

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  1. Chapter 21 Water Pollution

  2. POLLUTION OF FRESHWATER STREAMS • Flowing streams can recover from a moderate level of degradable water pollutants if they are not overloaded and their flows are not reduced. • In a flowing stream, the breakdown of degradable wastes by bacteria depletes DO and creates and oxygen sag curve. • This reduces or eliminates populations of organisms with high oxygen requirements.

  3. Water Pollution Problems in Streams • Dilution and decay of degradable, oxygen-demanding wastes and heat in a stream. Figure 21-4

  4. POLLUTION OF FRESHWATER STREAMS • Most developed countries have sharply reduced point-source pollution but toxic chemicals and pollution from nonpoint sources are still a problem. • Stream pollution from discharges of untreated sewage and industrial wastes is a major problem in developing countries.

  5. Global Outlook: Stream Pollution in Developing Countries • Water in many of central China's rivers are greenish black from uncontrolled pollution by thousands of factories. Figure 21-5

  6. Case Study: India’s Ganges River: Religion, Poverty, and Health • Religious beliefs, cultural traditions, poverty, and a large population interact to cause severe pollution of the Ganges River in India. • Very little of the sewage is treated. • Hindu believe in cremating the dead to free the soul and throwing the ashes in the holy Ganges. • Some are too poor to afford the wood to fully cremate. • Decomposing bodies promote disease and depletes DO.

  7. Case Study: India’s Ganges River: Religion, Poverty, and Health • Daily, more than 1 million Hindus in India bathe, drink from, or carry out religious ceremonies in the highly polluted Ganges River. Figure 21-6

  8. POLLUTION OF FRESHWATER LAKES • Dilution of pollutants in lakes is less effective than in most streams because most lake water is not mixed well and has little flow. • Lakes and reservoirs are often stratified and undergo little mixing. • Low flow makes them susceptible to runoff. • Various human activities can overload lakes with plant nutrients, which decrease DO and kill some aquatic species.

  9. Cultural Eutrophication • Eutrophication: the natural nutrient enrichment of a shallow lake, estuary or slow moving stream, mostly from runoff of plant nutrients from the surrounding land. • Cultural eutrophication: human activities accelerate the input of plant nutrients (mostly nitrate- and phosphate-containing effluents) to a lake. • 85% of large lakes near major population centers in the U.S. have some degree of cultural eutrophication.

  10. POLLUTION OF GROUNDWATER • Groundwater can become contaminated with a variety of chemicals because it cannot effectively cleanse itself and dilute and disperse pollutants. • The drinking water for about half of the U.S. population and 95% of those in rural areas comes from groundwater.

  11. Polluted air Pesticides and fertilizers Hazardous waste injection well Deicing road salt Coal strip mine runoff Buried gasoline and solvent tanks Gasoline station Pumping well Cesspool, septic tank Water pumping well Waste lagoon Sewer Leakage from faulty casing Landfill Accidental spills Discharge Unconfined freshwater aquifer Confined aquifer Confined freshwater aquifer Groundwater flow Fig. 21-7, p. 501

  12. POLLUTION OF GROUNDWATER • It can take hundreds to thousand of years for contaminated groundwater to cleanse itself of degradable wastes. • Nondegradable wastes (toxic lead, arsenic, flouride) are there permanently. • Slowly degradable wastes (such as DDT) are there for decades.

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

  14. POLLUTION OF GROUNDWATER • Leaks from a number of sources have contaminated groundwater in parts of the world. • According the the EPA, one or more organic chemicals contaminate about 45% of municipal groundwater supplies. • By 2003, the EPA had completed the cleanup of 297,000 of 436,000 underground tanks leaking gasoline, diesel fuel, home heating oil, or toxic solvents.

  15. Case Study: Arsenic in Groundwater - a Natural Threat • Toxic Arsenic (As) can naturally occur at high levels in soil and rocks. • Drilling into aquifers can release As into drinking water supplies. • According to WHO, more than 112 million people are drinking water with As levels 5-100 times the 10 ppb standard. • Mostly in Bangladesh, China, and West Bengal, India.

  16. OCEAN POLLUTION • Oceans, if they are not overloaded, can disperse and break down large quantities of degradable pollutants. • Pollution of coastal waters near heavily populated areas is a serious problem. • About 40% of the world’s population lives near on or near the coast. • The EPA has classified 4 of 5 estuaries as threatened or impaired.

  17. OCEAN POLLUTION • Harmful algal blooms (HAB) are caused by explosive growth of harmful algae from sewage and agricultural runoff. Figure 21-11

  18. Oxygen Depletion in the Northern Gulf of Mexico • A large zone of oxygen-depleted water forms for half of the year in the Gulf of Mexico as a result of HAB. Figure 21-A

  19. Missouri River Mississippi River Basin Ohio River Mississippi River MS LA LOUISIANA Mississippi River TX Depletedoxygen Gulf of Mexico Gulf of Mexico Fig. 21-A, p. 507

  20. Case Study: The Chesapeake Bay – An Estuary in Trouble • Pollutants from six states contaminate the shallow estuary, but cooperative efforts have reduced some of the pollution inputs. Figure 21-12

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

  22. OCEAN OIL POLLUTION • Tanker accidents and blowouts at offshore drilling rigs can be extremely devastating to marine life (especially diving birds, left). Figure 21-13

  23. PREVENTING AND REDUCING SURFACE WATER POLLUTION • The key to reducing nonpoint pollution – most of it from agriculture – is to prevent it from reaching bodies of water. • Farmers can reduce runoff by planting buffers and locating feedlots away from steeply sloped land, flood zones, and surface water.

  24. PREVENTING AND REDUCING SURFACE WATER POLLUTION • Most developed countries use laws to set water pollution standards, but such laws rarely exist in developing countries. • The U.S. Clean Water Act sets standards fro allowed levels of key water pollutants and requires polluters to get permits. • EPA is experimenting with a discharge trading policy similar to that for air pollution control.

  25. Reducing Water Pollution through Sewage Treatment • Septic tanks and various levels of sewage treatment can reduce point-source water pollution. Figure 21-15

  26. Reducing Water Pollution through Sewage Treatment • Raw sewage reaching a municipal sewage treatment plant typically undergoes: • Primary sewage treatment: a physical process that uses screens and a grit tank to remove large floating objects and allows settling. • Secondary sewage treatment: a biological process in which aerobic bacteria remove as much as 90% of dissolved and biodegradable, oxygen demanding organic wastes.

  27. Reducing Water Pollution through Sewage Treatment • Primary and Secondary sewage treatment. Figure 21-16

  28. Reducing Water Pollution through Sewage Treatment • Advanced or tertiary sewage treatment: • Uses series of chemical and physical processes to remove specific pollutants left (especially nitrates and phosphates). • Water is chlorinated to remove coloration and to kill disease-carrying bacteria and some viruses (disinfect).

  29. Reducing Water Pollution through Sewage Treatment • Sewage sludge can be used as a soil conditioner but this can cause health problems if it contains infectious bacteria and toxic chemicals. • Preventing toxic chemicals from reaching sewage treatment plants would eliminate such chemicals from the sludge and water discharged from such plants.

  30. Odors Odors may cause illness or indicate presence of harmful gases. Dust Particles Particles of dried sludge carry viruses and harmful bacteria that can be inhaled, infect cuts or enter homes. BUFFER ZONE Exposure Children may walk or play in fertilized fields. Livestock Poisoning Cows may die after grazing on sludge-treated fields. Sludge Groundwater Contamination Harmful chemicals and pathogens may leach into groundwater and shallow wells. Surface Runoff Harmful chemicals and pathogens may pollute nearby streams,lakes, ponds, and wetlands. Fig. 21-17, p. 513

  31. Reducing Water Pollution through Sewage Treatment • Natural and artificial wetlands and other ecological systems can be used to treat sewage. • California created a 65 hectare wetland near Humboldt Bay that acts as a natural wastewater treatment plant for the town of 16,000 people. • The project cost less than half of the estimated price of a conventional treatment plant.

  32. Reducing Water Pollution through Sewage Treatment • Water pollution laws have significantly improved water quality in many U.S. streams and lakes but there is a long way to go. • Some want to strengthen the U.S. Clean Water Act (CWA) to prevent rather than focusing on end-of-the-pipe removal. • Many farmers and developers see the CWA as limiting their rights as property owners to fill in wetlands.

  33. DRINKING WATER QUALITY • Centralized water treatment plants and watershed protection can provide safe drinking water for city dwellers in developed countries. • Simpler and cheaper ways can be used to purify drinking water for developing countries. • Exposing water to heat and the sun’s UV rays for 3 hours can kill infectious microbes.

  34. Using Laws to Protect Drinking Water • While most developed countries have drinking water quality standards and laws, most developing countries do not. • The U.S Safe Drinking Water Act requires the EPA to establish national drinking water standards (maximum contaminant levels) for any pollutant that may have adverse effects on human health.

  35. Using Laws to Protect Drinking Water • The U.N. estimates that 5.6 million Americans drink water that does not meet EPA standards. • 1 in 5 Americans drinks water from a treatment plant that violated one or more safety standard. • Industry pressures to weaken the Safe Drinking Act: • Eliminate national tests and public notification of violations. • Allow rights to pollute if provider cannot afford to comply.

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

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