Water Filtration


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EPA ENVIRONMENTAL EDUCATION WATER FILTRATION BACKGROUND: Water in lakes, rivers, and swamps often contains impurities that make it look and smell bad. The water may also contain bacteria and other microbiological organisms that can cause disease. Consequently, water from surface water sources must be “cleaned” before it can be consumed by people. Water treatment plants typically clean water by taking it through the following processes: (1) aeration; (2) coagulation; (3) sedimentation; (4) filtration; and (5) disinfection. Demonstration projects for the first four processes are included below. OBJECTIVE: To demonstrate the procedures that municipal water plants use to purify water for drinking. MATERIALS NEEDED: 5 liters of “swamp water” (or add 2 ½ cups of dirt or mud to 5 liters of water) 1 two-liter plastic soft drink bottle with its cap (or cork that fits tightly into the neck) 2 two-liter plastic soft drink bottles—1 with the top removed, 1 with the bottom removed 1 one-and-one-half-liter (or larger) beaker (or another soft drink bottle bottom) 20 grams of alum (potassium aluminum sulfate—approximately 2 tablespoons) (Hint: should be available in pharmacy or spice aisle in grocery store) Fine sand (about 800 ml in volume) Course sand (about 800 ml in volume) Small pebbles (about 400 ml in volume) (Hint: washed natural color aquarium rocks will work) 1 large (500 ml or larger) beaker or jar 1 coffee filter 1 rubber band 1 tablespoon 1 clock with a second hand (or a stopwatch) PROCEDURE: 1. Pour about 1.5 liters of the swamp water into a 2-liter bottle. Have students describe the appearance and smell of the water. 2. Aeration is the addition of air to water. It allows gases trapped in the water to escape and adds oxygen to the water. Place the cap on the bottle and shake the water vigorously for 30 seconds. Continue the aeration process by pouring the water into either one of the cut-off bottles, and then pour the water back and forth between the cut-off bottles 10 times. Ask students to describe any changes they observe. Pour the aerated water into a bottle with its top cut off. 3. Coagulation is the process by which dirt and other suspended solid particles are chemically “stuck together” into floc so that they can be removed from water. With the tablespoon, add 20 grams of alum crystals to the swamp water. Slowly stir the mixture for 5 minutes.

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