1. Water Purification and Treatment Natural and Municipal

2. American History of Water Purification Wastewater (including human wastes) was dumped into holes, dry wells, leaching cesspools (pits lined with broken stone), into rivers, lakes, or onto the ground. Until the late 1800s, Americans got their water from ponds, lakes, rivers, wells, and rainwater holding tanks.

3. By the late 1800s, cities and towns were constructing sewer systems, and about one-quarter of all urban households had a flush toilet However, some sewer wastes were still dumped WITHOUT treatment into lakes and streams Other cities and towns were downstream and this polluted their water

4. Many community leaders believed that natural waters would purify themselves. But, as population increased, diseases carried by water also increased and the concentration of intestinal bacteria in drinking water rose. E coli bacteria Cholera bacteria

5. As a direct result, water filtering and chlorination of a community’s water soon began. Nowadays, communities are also responsible for treating their wastewater BEFORE it is released into the environment

6. Global Water-Purification System We can think of the hydrological cycle as the Earth’s NATURAL water-purification system, powered by the sun. OCEANS – the primary water source ATMOSPHERE – the principal carrier of water LAND – the location of the major water users Overall, water is neither LOST nor GAINED

7. Purifying Water through the Hydrological Cycle  The hydrological cycle-- evaporation, condensation, precipitation, infiltration and runoff--removes most dissolved substances

8. Evaporation, Condensation Thermal energy from the Sun causes water to evaporate from oceans and other water sources Dissolved heavy metals, minerals and molecular substances are left behind Precipitation  Pure rainwater and snowflakes are the best natural supply of clean water  There is some contamination from atmospheric gases (natural and human- caused)

9. Infiltration and Runoff  When rainwater and snowmelt are absorbed by soil (infiltration) or travel over the soil surface (runoff), then impurities (such as organic substances from living creatures) become suspended or dissolved in this water.  A few cm below the surface, bacteria feed on these substances and turn them into carbon dioxide, water and other simple compounds, repurifying the water.

10. Filtration at Deeper Levels  At deeper levels, water passes through gravel, sand and even pores in rock (filtration) where bacteria and suspended material are filtered out Slightly acidic groundwater passing through rocks with soluble compounds (e.g., magnesium and calcium minerals) ADDS minerals to water, making the water ‘hard’

11. Summary of Nature’s Water- Purification System These three processes make up the natural water purification system: Evaporation, followed by condensation, removes nearly all dissolved substances Bacterial action converts dissolved organic contaminants into simple compounds Filtration through sand and gravel removes nearly all suspended matter

12. Can we depend on nature to purify our water? If the conditions are right, we could depend on this natural purification system. This means the water has (1) ENOUGH TIME in the soil to have bacteria clean it and (2) traveling through ENOUGH SAND and GRAVEL to filter it. This system does NOT work if it is OVERLOADED or water is drawn from it before it can be cleansed.

13. Reservoir Model Another way to think of the Hydrological Cycle is as a model made up of various reservoirs with water simultaneously entering and leaving these reservoirs. Oceans Atmosphere Glaciers, ice caps Seasonal snow cover Shallow groundwater Deep groundwater Soil moisture

14. The RESIDENCE TIME or storage time in these reservoirs can be as short as days or as long as thousands of years. The reservoirs with the lowest water capacity tend to have the shortest residence time because they have large inputs and outputs.

15. Oceans Atmosphere Glaciers, ice caps Seasonal snow cover Shallow groundwater Deep groundwater Soil moisture Atmosphere: replaced every 8 days Glaciers and ice caps: 20 to 100 years Soil moisture: 1-2 months Seasonal snow cover: 2-6 months Shallow groundwater: 100 to 200 years Deep groundwater: to 10,000 years (e.g., Ogallala aquifer in central and western US)

16. Municipal Water Treatment Water taken from rivers and lakes for community use is cleaned twice, both before and after it is used. Pre-use purification is usually called water treatment.

17. Screening Prechlorination Flocculation Settling Sand filtration Post-chlorination Optional further treatment: 1)Aeration 2)pH adjustment 3)Fluoridation Water source: River, lake, reservoir Houses, businesses, schools, etc.

18. Municipal Water Treatment 1.Filtering through metal screens to remove fish, sticks, beverage containers, etc. 2.Prechlorination—chlorine may be added because it is a powerful disinfecting agent.

19. Municipal Water Treatment 3.Flocculation —Alum (aluminum sulfate) and slaked lime (calcium hydroxide) are added to remove suspended particles. They react together to form aluminum hydroxide, a sticky, jelly-like material that traps the suspended particles. This is allowed to settle out.

20. Municipal Water Treatment 4.The water is further filtered by passing through sand to remove any remaining suspended particles. 5.Post-chlorination—operators adjust the chlorine concentration to make sure there is a low but sufficient level to protect the water from bacterial infestation.

21. Municipal Water Treatment 6.There may be several more steps, such as aeration (spraying the water into the air to remove odors and improve taste), pH adjustment, and fluoridation (to reduce tooth decay).

22. Chlorination of Water Chlorination, the addition of chlorine to water to kill harmful organisms, is done in several ways: 1.Chlorine gas (Cl 2 ) is bubbled into the water. The gas is not very soluble in water but does produce a water- soluble chlorine compound. “The single most common cause of human illness … is unhealthful water supplies.” (p.90, text)

23. 2.A water solution of sodium hypochlorite, the active ingredient in household bleach, is added. 3.Calcium hypochlorite, either as small pellets or a powder, is dissolved in the water. This substance is commonly used in swimming pools and is an ingredient in bleaching powders used in the home.

24. Pros and Cons of Chlorination Under some conditions, chlorine in water reacts with organic compounds produced by decaying organic material (plant and animal) to form substances harmful to human health. One group of such substances is TRIHALOMETHANES (THMs). Chloroform is a THM and a carcinogen.

25. The EPA has placed a limit of 80 ppb on THM concentration in municipal water-supply systems. The benefit of using chlorination to purify water supplies has to be balanced against the risk from THMs. Are there any alternatives?

26. Eliminating THM Health Risks 1.Pass treated water through ACTIVATED CHARCOAL. Disadvantage: Charcoal filters are expensive to install and operate. Also, they need to be replaced often.

27. Eliminating THM Health Risks 2.Don’t use charcoal at all—instead, use ozone (O 3 ) or ultraviolet (UV) light to disinfect the water. Disadvantage: Doesn’t protect the treated water from becoming recontaminated. Also, ozone itself can be hazardous if not handled properly.

28. Eliminating THM Health Risks 3.Eliminate the pre-chlorination step. Chlorine would be added only once, after most of the organic material has been removed. Disadvantage: THMs can still form, and the lower chlorine concentration could lead to bacterial growth.