"APESlec ppt ch22 Water Pollution"
Chapter 22 Water Pollution and Treatment 1 Water Pollution Water Pollution – degradation of water quality making it unsuitable for its intended use. Types of pollutants can be biological pathogens, industrial chemicals, heavy metals, fertilizers , sediment, heat, radioactive isotopes, fecal Coliform bacteria, sewage, nutrients or organic materials ThePrimary water pollution problem in the world is lack of clean drinking (potable) water 2 Biochemical Oxygen Demand (BOD) The amount of oxygen required for biochemical decomposition process 3 zones 1. A pollution zone – where pollutants are dumped. High BOD 2. An active decomposition zone – dissolved oxygen is at a minimum 3. A recovery zone - Oxygen recovering to normal level 3 4 Waterborne Disease Outbreaks of waterborne diseases Milwaukee, WI : March 11 – April 9 1993 • 400,000 people out of 1.6 million were infected after drinking the water. 100 people died Fecal Coliform Bacteria: • a standard way of measuring bacterial contamination. It is present in all human and animal wastes. E. coli bacteria in this type of pollution. Its presence in water makes it unsafe for drinking. Various outbreaks related to E coli have occurred over the years. Walkerton, ON –May 2000. a town of 5,000. E. Coli from cow manure washed into the water supply. Water company did not inform public to boil water even when it knew the water was contaminated. 5 people died and 500+ got sick. 5 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. 6 Water Pollution Problems in Streams and decay of degradable, oxygen- Dilution demanding wastes and heat in a stream. 7 Figure 21-4 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. 8 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. 9 Figure 21-5 Nutrients Eutrophication The process by which a body of water develops a high concentration of nutrients Cultural Eutrophication When eutrophication is accelerated by human processes that add nutrients to a body of water In either case the lake or body of water can become unusable or void of living organisms 10 11 EUTROPHICATION Harmful changes in water caused by too much fertilizer or nutrients getting into the water. 12 STEPS OF EUTROPHICATION 1. Fertilizer flows 2. Increased plant growth on into water the surface of water, causing….. causing…. 3. Decreased light in lower levels of water, causing… 13 STEPS OF EUTROPHICATION 4. Plants in lower levels of 6. Death of fish and water to die, causing…. other animals. 5. Decay using up O2 and increasing CO2,causing…... 14 These fish died due to eutrophication removing the oxygen. 15 Three Causes of Eutrophication: Fertilizeror manure runoff from farmland. Improper disposal of sewage. Chemical and industrial waste. 16 Compare the water upstream from the dam to downstream, what differences do you see? 17 Wastewater Treatment Two Methods- for processing sewage Septic Tank Disposal Systems • Underground tank that lets water flow out but retains solids. Usually found at Private residences Waste Treatment Plants - municipalities • Primary Treatment –required by law • Secondary Treatment- required by law unless waiver is obtained • Advanced Treatment – if discharge is not clean enough for the environment it is being discharged into e.g. to remove phosphates , organic chemicals etc • Chlorine Treatment – disinfectant 18 Reducing Water Pollution through Sewage Treatment Septic tanks and various levels of sewage treatment can reduce point-source water pollution. 19 Figure 21-15 Manhole cover (for cleanout) Septic tank Gas Distribution box Scum Wastewater Sludge Drain field (gravel or crushed stone) Vent pipe Perforated pipe 20 Fig. 21-15, p. 510 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. 21 Reducing Water Pollution through Sewage Treatment Primary and Secondary sewage treatment. 22 Figure 21-16 Primary Secondary Chlorine Bar screen Grit chamber Settling tank Aeration tank Settling tank disinfection tank To river, lake, Sludge or ocean Raw sewage Activated sludge (kills bacteria) from sewers Air pump Sludge digester Disposed of in landfill or ocean or applied to Sludge drying bed cropland, pasture, or rangeland 23 Fig. 21-16, p. 511 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). 24 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. 25 26 Thermal Pollution of Waters Effects of Current and Planned Nuclear Generating Plants on the Tennessee River 27 What is Thermal Pollution? Increase in the normal temperatures of natural waters caused by intervention of human activities. Temperature is a physical characteristic of water which is regulated under the Clean Water Act 28 Nuclear Power Plants Nuclear power plants use water as a cooling agent. After the water is used, it is put back into a water supply at 9-20oC warmer This 1988 thermal image of the Hudson River highlights temperature changes caused by discharge of 2.5 billion gallons of water each day from the Indian Point power plant. The plant sits in the upper right of the photo — hot water in the discharge canal is visible in yellow and red, spreading and cooling across the entire width of the river. Two additional outflows from the Lovett coal-fired power plant are also clearly visible against the natural temperature of the water, in green and blue. 29 Thermal Pollution Suffocated fish Altered food web Low Decreased fish dissolved population oxygen 30 Waste Heat from Power Plants 31 Exxon Valdez Oil Spill 1989 http://www.bbc.co.uk/mediaselector/check/player/nol/news id_6720000/newsid_6724300?redirect=6724373.stm&new s=1&nbwm=1&nbram=1&bbwm=1&bbram=1 32 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. 33 OCEAN POLLUTION Harmfulalgal blooms (HAB) are caused by explosive growth of harmful algae from sewage and agricultural runoff. 34 Figure 21-11 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. 35 Figure 21-A Missouri River Mississippi River Basin Ohio River Mississippi River MS LA LOUISIANA TX Mississippi River Depleted oxygen Gulf of Mexico Gulf of Mexico 36 Fig. 21-A, p. 507 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. 37 Figure 21-12 OCEAN OIL POLLUTION ocean oil pollution comes from Most 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. 38 OCEAN OIL POLLUTION Tanker accidents and blowouts at offshore drilling rigs can be extremely devastating to marine life (especially diving birds, 39 Figure 21-13 Acid Mine Drainage Water with a high concentration of sulfuric acid that drains from mines. Tailings contain sulfur Serious water pollution problem Damages aquatic ecosystems, pollutes bodies of water and degrades water quality 40 Surface Water Pollution Water Pollutants are emitted from Point Sources • Distinct and confined sources such as pipes from industrial or sites Nonpoint Sources • Diffused and intermittent runoffs from streets – waste, oil, litter etc. Runoff from farms – pesticide, fertilizers, sediment etc. Two approaches to surface water pollution Reduce the source Treat water to remove the pollutant 41 Groundwater Pollution Half the U.S. gets its drinking water from ground water. Groundwater can become polluted from many sources. Example of groundwater pollution is on the next slide. Issues: Lack of oxygen - kills aerobic bacteria but supports anaerobic bacteria; pollutants do not breakup readily in water; slow cycling of water with little opportunity for dispersion or dilution Bioremediation: a method of treating groundwater pollution problems that utilizes microorganisms in the ground to consume or break down pollutants. 42 Groundwater Pollution from a buried gasoline tank 43 Groundwater pollution through saltwater intrusion. A problem for Long Island Pumping the well too hard may draw saltwater into the well 44 Wastewater Renovation and Conservation Cycle An Idealized concept of wastewater usage Steps: 1. Return of treated (primary ) wastewater to crops 2. Renovation or natural purification by slow percolation of the wastewater into soil to eventually recharge the groundwater resource with clean water 3. Reuse of the treated water 45 Wastewater Renovation and Conservation Cycle 46 Water Reuse Inadvertent: water is withdrawn, treated and returned to the environment – followed by further withdrawals and use. For example: Sewage plants discharge water into the river, downstream communities withdraw this water. Indirect: Ex) the wastewater renovation and conservation cycle Direct: The use of treated wastewater that is piped directly from a treatment plant to the next user 47 Water Pollution and Environmental Law Environmental Law The branch of law dealing with conservation and use of natural resources and control of pollution e.g. Clean Water Act of 1972 amended 1977 48