CHAPTER 20

1. CHAPTER 20 Water Pollution and Its Prevention

2. 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

3. The 2008 dead zone in the Gulf of Mexico

4. 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

5. 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

6. 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

7. 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

8. Cuyahoga River on fire

9. 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

10. Point and nonpoint sources

11. 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

12. The Ganges River in India

13. 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

14. Worldwide distribution of improved sanitation

15. 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

16. 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

17. The oxygen sag curve

18. 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

19. Acid mine drainage

20. 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

21. Stream ecosystem with low bed load

22. 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

23. Impact of sediment on streams and rivers

24. Storm-water management

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. A diagram of wastewater treatment

35. 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

36. 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

37. Trickling filters for secondary treatment

38. 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

39. Biological nutrient removal (BNR)

40. 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

41. 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

42. 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

43. Anaerobic sludge digesters

44. Dewatering treated sludge

45. 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

46. 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

47. Septic tank treatment

48. 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

49. 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%

50. Composting toilet system