2) List three major processes that occur in natural water purification and, for each, identify the contaminants that the process removes.
1) Evaporation of water vapor and condensation of water droplets in clouds: removes nearly all dissolved substances.
2) Bacterial action: converts dissolved organic contaminants into simple compounds.
3) Filtration through sand and gravel: removes nearly all suspended matter.
3) How are the properties of aluminum hydroxide related to the process of flocculation?
Aluminum hydroxide is formed by alum and slaked lime. It is a sticky, jellylike material that traps and removes the suspended particles in the water-- flocculation.
4) Why is calcium oxide (CaO) sometimes added in the final step of municipal water treatment?
Sometimes, water is acidic enough to dissolve metallic water pipes. This could result in the entrance of undesirable ions into the water supply. Lime, or calcium oxide, is added in the final step of municipal water treatment because it is basic and it neutralizes acidic water by raising its pH to a proper level.
5) Fluoride, an ingredient in many types of toothpaste, is sometimes added to municipal water supplies in the last stage of water treatment. How much fluoride is added and what is its purpose?
As much as 1 ppm of fluoride is sometimes added to municipal water supplies in the last stage of water treatment because it reduces tooth decay.
6) What are advantages of chlorinated drinking water compared to untreated water?
Chlorinated drinking water has saved countless lives because it controls waterborne diseases by killing disease-producing microorganisms. Chlorine kills dangerous bacteria and along with other purification processes, makes water safe to drink.
7) Is there a disadvantage to using chlorination in water treatment? Explain.
Yes. Chlorine in water can react with organic compounds made by decomposing animal and plant water to form substances that can be harmful to humans. One group of the substances, trihalomethane (THM), such as chloroform, is a cancer causing substance, or a carcinogen. These substances are very dangerous to human health.
8) Water from a clear mountain stream may require chlorination to make it safe for drinking. Explain.
Water from a clear mountain stream may require chlorination to make it safe for drinking due to various types of bacterias found on the ground, such as feces left by animals, or dirty substances added to the water through animals drinking and bathing in the water.
9) List two alternatives to the use of chlorination in municipal water treatment.
1) Charcoal filters: they remove most organic compounds from water, including THMs *(but they are expensive, hard to clean, and need to be replaced often).
2) Ozone or ultraviolet light: these disinfect water *(but do not protect the water once it has left the treatment center).
18) Explain what would happen to Earth's hydrologic cycle if water evaporation suddenly stopped.
Evaporation is the starting point of the hydrologic cycle, and if evaporation suddenly stopped, so would condensation and precipitation. Although the water underground may continue to flow for a period of time, it would never be replenished by rain water or snow and eventually dry out; the hydrologic cycle would stop.
19) One unique characteristic of water is that it is present in all three physical states (solid, liquid, and gas) in the range of temperatures found on Earth. How would the hydrologic cycle be different if this were not true.
The hydrologic cycle involves all three physical states (solid, liquid, and gas). Water evaporates as vapor, or a gas, condenses into tiny water droplets in clouds (liquid), and falls as either rain water (liquid), snow, or hail (solids). If this were not true, the hydrologic cycle would not function the way it does, and not be able to exist.
20) Why does the EPA limit the concentration of THMs to 80 ppb instead of requiring their total elimination from municipal water supplies.
The alternatives to the use of chlorination carry disadvantages, and since very little amounts (80 ppb) of THMs should not have much effect on the human body, the EPA recognizes the difficulties of using alternatives and accepts the substance in extremely low concentrations.
21) Compare how the various processes used in the foul-water investigation (page 10) are similar to steps in the natural purification of water.
The processes of evaporation and condensation mimic the process of distillation and what happens in a distillation apparatus on a grander scale. Also, when water seeps into the ground and it passes through gravel, sand, and rock, suspended mater are filtered out; this is like the sand filtration process used in the foul-water investigation.
22) Some physicians recommend consuming about 2 L of water daily. Municipal water supplies may contain up to 1 ppm fluoride. Assume that you drink 2 L of water per day. At 1 ppm fluoride, how many grams of fluoride ion would you consume in
a. one day?
b. one week?
c. one year?
a. 1 ppm fluoride.
b. 7 ppm fluoride.
c. 365 ppm fluoride.
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