2. - Evaporation, followed by condensation, removes nearly all dissolved substances.
- Bacterial action converts dissolved organic contaminants into a few simple compounds.
- Filtration through sand and gravel removes nearly all suspended matter.
3. The alum and slaked lime react to form aluminum hydroxide, which is a sticky, jellylike material that traps and removes the suspended particles, a process called flocculation.
4. A plant may add CaO to neutralize such acidic water, thus raising its pH to a proper level.
5. As much as about 1 ppm of fluoride ion (F-) may be added to the treated water in a process known as fluoridation. Fluoride ions can reduce tooth decay even at very low concentration.
6. Chlorine kills disease-producing microorganisms.
7. Chlorine does have disadvantages. One being that in sufficiently high concentrations, it can be harmful to human health. Chlorine produces some substances that are known to cause cancer.
8. Water from a mountain stream may have bacteria that chlorine can remove.
9. Using ozone or eliminate prechlorination.
18. If water evaporation suddenly stopped, so would the hydrologic cycle because evaporation is a key step to the hydrologic cycle.
19. The hydrologic cycle causes water to evaporate (making it a gas), causes rain to fall (making it a liquid), and causes sleet, snow or hail. The hydrologic cycle would not work normally if water was not in the form of these three substances.
20. The EPA has placed a current limit of 80 parts per billion on total THM concentration in municipal water-supply systems because of possible risks associated with THMs.
21. A charcoal filter can be used (similar to the charcoal adsorption), there is filtration for both, and filtration through sand and gravel (similar to the sand filtration).
22. A. 1,000,000
B. 7,000,000
C. 365,000,000
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