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Chapter 17 Water Pollution

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1 Chapter 17 Water Pollution

2 Types of Pollutants Pathogens = disease causing bacteria, viruses and organisms, often found in high levels in human and animal excrement Organic Wastes Chemical Sediments Nutrients Pollution = “the presence of a substance in the environment that because of its chemical composition or quantity prevents the functioning of natural processes and produces undesirable environmental and health effects.”

3 DO in water Dissolved oxygen (DO) can be up to 10ppm (parts per million) in cold water, but usually less in warm water Compare that to a ratio of 200,000 ppm (20%) in air and you can understand why just moderate drops in DO can be dangerous to an ecosystem

4 BOD Dissolved oxygen (DO) in the water is depleted during decomposition of organic wastes. Water quality test. Biochemical oxygen demand (BOD): measure of the amount of organic material. High BOD means a lot more oxygen needed for bacteria to decompose all the organic material Higher BOD usually is a worse situation due to too much dead organic material

5 In the U.S. Sewage treatment is a common practice
In the 1970’s many cities were still dumping raw sewage into waterways In 1972, the Clean water act is chief federal law to govern water pollution, provided funding for upgrading sewage treatment plants In 1974, the Safe Drinking Water Act ensures safe drinking water for the public in the US Currently water ways are the much better 1°, 2° use preliminary but no more Test for sewage contamination in drinking H2O  Fecal Coliform test

6 Sewage Treatment Preliminary Treatment = removal of debris and grit with bar screen and grit chamber (settling pool for just big grit)

7 Sewage Treatment Primary Treatment = Removal of Particulate Organic Material  fats and oil float and are skimmed off while organic raw sludge sinks to bottom

8 Sewage Treatment Secondary Treatment or Biological Treatment: Removal of Colloidal and Dissolved Smaller Organic matter using decomposiing organisms to metabolize it called an acitivated sludge system with aeration bubbles

9 Another form of Secondary Treatment
Trickling Filter System: the water exiting primary treatment is sprinkled onto, and allowed to trickle through a bed of 6-8 feet of fist sized rocks Spaces for good aeration and microorganisms on the rocks decompose dissolved organic material

10 Sewage Treatment Raw sewage straight from homes and industry (99% H2O ;only 1% waste, paper,other) Preliminary Treatment- allow grit to settle 1° separating Raw Sludge particulate organic matter from H2O 2° AKA Biological Treatment- aerobic bacteria feeds on the organic material Trickling filters contain bacteria  remove raw sludge from the H2O 3° treatment would remove heavy metals and toxic chemicals but this is not usually done

11 Treatment Options for the Raw Sludge
Anaerobic Digestion allowing bacteria to produce biogas (2/3 methane gas CH4 and other is CO2 and foul smelling organic compounds) Composting with oxygen environment to produce humus-like material for treating poor soil Pasteurization = heating sufficiently in oven to kill pathogens and packed into pellets for fertilizer

12 Sewage Treatment cont’d
Categories of sewage treatment: Debris, particulate organics, colloidal + dissolved organics, dissolved inorganics Raw Sludge May contain heavy metals If it does it needs 3° treatment, to remove the toxic chemicals

13 Sewage Treatment cont’d
If raw sludge does not contain toxic chemicals, it may be… Anaerobically (without O2) decomposed with bacteria and microorganisms Composted Applied to farms after treatment Waste water in the US has a post treatment of adding Chlorine gas to the H2O as disinfectant  This can lead to the formation of hazardous chlorinated hydrocarbon components which is of concern

14 Home Septic systems Home Septic Systems: do not use Chlorine
Do use settling tank to settle organic solids Lets waste water percolate into the soil bacterial decomposition

15 Septic Tank

16 Problems Point Source Pollutants
Enter from a specific source such as a pipe, a factory, etc. Easiest to monitor and test Locations evident Permits are required for pollutants Eutrophication Excess Nitrogen and Phosphorous




20 Hypoxic Zones or Dead Zones Eutrophication to the extreme
Nitrogen “enriches” the waters  promotes dense growth of photosynthetic phytoplankton (blocking light for benthic organisms)  zooplankton rapidly consume phytoplankton and multiply Their fecal pellets and dead bodies sink to bottom and are decomposed aerobically by bacteria  decomposition activity leads to extreme lowering of oxygen levels  making it hypoxic and many higher animals die off Happens in Gulf of Mexico from May through September effecting Louisiana and Texas

21 Gulf of Mexico Dead Zone


23 Other Water Info Relative Humidity = the amount of water vapor in the air compared to what the maximum it can hold at that temperature Average US person uses 100 gallons of water per day mostly used to rinse, clean and wash away unwanted material Most of the water in the US and in the world is used by humans for irrigatino of agriculture

24 Water Conservation Efforts
Reuse of gray water (the water that comes from sinks, showers and laundry) for water of plants or grass Xeriscaping where drought resistant and native plants are used instead of water needy plants like grass lawns

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