24-12-2012, 05:03 PM
WATER PURIFICATION
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Background
The quality of the water you get from your tap is not something to be taken for granted.
Rather, all public drinking water produced and delivered for human consumption must meet
or exceed the standards established by state health departments and the Environmental
Protection Agency. These standards are stricter than the quality standards set for anything
else we eat or drink.
Each year, water companies collect hundreds of water samples from wells, reservoirs,
and point-of-use locations. Highly trained chemists, microbiologists, and laboratory
technicians in certified laboratories test these samples. Untreated water usually contains
many inorganics, such as sodium, potassium, calcium, magnesium, iron, chloride, sulfates,
and phosphates. The untreated water also may contain some dissolved gases like oxygen,
nitrogen, and carbon dioxide. Therefore, water may be treated differently in different
communities depending on the quality of the water that enters the treatment plant.
Groundwater, water located under ground, typically requires less treatment than water from
lakes, rivers, and streams.
Introduction to Water Treatment
When a water supplier takes untreated water from a river or reservoir, the water usually
contains dirt and tiny pieces of leaves and other organic matter, as well as trace amounts of
certain contaminants that need to be removed. Water treatment follows simple principles of
separation of materials in addition to biological treatment methods. The treatment of
municipal water supplies commonly involves the following steps (Figure 1):
1. Coarse Filtration. Water from the source is passed through a wire screen.
2. Bacteria Removal. Chemical additives may be used to water.
3-4. Sedimentation. Solid particles in water settle to the bottom over a few days.
5. Sand Filtration. Water filters through sand, removing any fine solids.
6. Aeration. Air is bubbled through the liquid, removing some organic material.
7. Sterilization. Chlorine sometimes is added to kill bacteria.
8. Storage. Water is stored before being sent to users.
Laboratory Activities
Although an actual water treatment plant uses more advanced equipment, this laboratory
focuses on the same physical methods to separate contaminating materials and substances
from water. These methods are: extraction, filtration, distillation, and phase separation.
In this exercise you will work in assigned groups to:
• Test each of the physical methods of separation using different untreated water
samples in order to deduce the purpose and the limitations of each method.
• Design, test, and evaluate a purification treatment method for a given sample of
very dirty and odorous water.
• Create a poster of your findings for presentation to the class.
Purification of Water by Phase Separation
Procedure
1. Obtain a piece of tubing and clamp it to the glass funnel as shown in Figure 4.
2. Pour the mixture of liquids into the funnel and let it set until the two layers are
completely separated.
3. Unclamp the tube to allow the bottom layer to drain into the jar.
4. Clamp the tube just before the top layer is about to pass through the tube.
5. Record your observations in the Table 4.