For Students Engineering Design in Oregon Science Classrooms Page 1 of 1 Filled Data Table Handout for Bioswales Introduction: In the next part of this lesson, you will be designing water filters. For your filter you will need to decide on the amount, combination, and sequence of materials that will best clean polluted water. Knowing the filtration abilities of cheesecloth, sand, gravel, rock, and limestone will help you determine these values. (Note: In this water filter model the cheesecloth represents plant roots.) Turbidity is a measure of the cloudiness of a liquid caused by solid particles. If these particles are large, they generally settle to the bottom of the liquid. However, smaller particles too tiny to see with the naked eye stay suspended, discoloring the liquid, just like smoke particles float in the air and make it hazy. Since high turbidity in water is a sign there are many foreign substances mixed in, it is a key test of water quality. Pure water has a pH close to 7 at room temperature. Deviations from this neutral pH indicate the presence of chemicals in the water. Acidic substances like sulfuric acid and many types of fertilizers will decrease the pH value, while alkaline substances — soaps, bleach, and calcium carbonate (limestone and Tums) — increase water’s pH value. Although natural water systems are usually slightly acidic or slightly basic, they are safe. But pollution may cause too much deviation from neutral, and the environment suffers because most aquatic animals and plants have adapted to life in water with a specific, narrow pH range. That is why pH is another good test of water quality. Filter Material 2.5cm x2.5cm Cheesecloth Square (4 ply) 1/3 Cup Sand & Cheesecloth Square Infiltration Time Change in Turbidity Change in pH Observations Tea particles caught in cheesecloth. 10.24 sec 0 0 Cheesecloth stained green. Takes a moment for solution to begin dripping 5.82 min +7 0 Tea particles caught in sand. Sand has green tint after filtration 1/3 Cup Gravel & Cheesecloth Square 23.83 sec 0 0 Tea particles caught in gravel. 1/3 Cup Rocks & Cheesecloth Square 17.82 sec 0 0 Tea particles caught in rocks. 1/3 Cup Limestone & Cheesecloth Square Did not filter enough to measure turbidity. - - +1 Tea particles caught in limestone. Becomes more grey and somewhat turbid.