Water Treatment 101 Objective: There are two main objectives to this lesson. The first being the student understands the basic water cycle and how important it is to keep the fresh water we have clean and usable. The second is to open the student mind to some basic chemistry that is widely used to help clean the water before it re-­‐enters the water cycle. Background: Water is our most common natural resource. It is essential to the Biology and Chemistry of all living things, it plays a major role in shaping the Earth and is an active agent in many physical reactions. It is important to most life to keep it clean. There is plenty of water on Earth, but 97% of this water is saline (contains dissolved salts). Only 3% is fresh and about two thirds of that amount is locked up in polar ice caps and glaciers; about one third can be found as groundwater, lakes, and in the atmosphere. Water exists in three states of matter: solid (ice), liquid (water), and gas (vapor) at normal conditions. Water is a colorless, odorless, tasteless liquid with a melting point of 0° centigrade and a boiling point of 100°centigrade. Water can be easily cleaned through the water cycle. When water evaporates in the gaseous phase, it leaves all the impurities behind. Water can also be cleaned through other natural ways. Humans have created ways in which they can also clean water without going through a natural water cycle. The treatment of water has been around since early man. The Ancient Egyptians describe water purification by boiling, exposure to sunlight, charcoal filtration, and settling in an earthen jar. In 400 B.C., it was suggested that water should be boiled and strained through a piece of cloth to remove particles. It wasn’t until the early 20th century, however, that a method of purification was developed that virtually eliminated water borne diseases such as cholera and typhoid fever. Today there are several methods used in the treatment of water being drinking water, wastewater, or stormwater. These methods include disinfectants, coagulation/flocculation, settling, and filtration. In this demonstration we are going to observe the chemistry behind coagulation/flocculation/settling to gain knowledge of these processes. Water Cycle Procedure: 1. Discuss with students the following major points of the water or hydrologic cycle. Draw the water cycle and explain the following: a. Precipitation in forms of rain, snow, sleet or hail comes from clouds. b. Depending on a number of factors such as soil type, slope, moisture conditions, and intensity of precipitation will either infiltrate into the ground or runoff into rivers and streams. c. Virtually no water infiltrates through paved roads and parking lots, so almost all of it becomes urban runoff. Runoff from rivers and streams is stored in large bodies of water such as lakes, estuaries, and oceans. d. Water is returned to the atmosphere evaporation from the surface of land or water bodies, or through plants by a process called transpiration. e. Clouds are formed by condensation of water vapor that is evaporated from the land or oceans. 2. The newest water we see is rain and the oldest water in the cycle is from the ocean. Chemistry Procedure: 1. Discuss with students the nature of particulate impurities in water. Particulates are a very small solid suspended in water which can vary widely in size, shape, density, and electrical charge. An example of suspended solids in water can be the result of land or urban runoff to a river or stream. 2. Discuss how the electrical charge of these particles can be used to help settle the suspended solids through coagulation/flocculation. To help the student understand electrical charges of particles the following demonstration and discussion can be conducted. Atoms are the building blocks of matter. They are composed of neutral particles with no electric charge and protons with a positive charge in the center or nucleus. On the outside of the nucleus, electrons with a negative charge encircle the positive charge of the protons within the nucleus. Opposite charges, positive and negative, are attracted to one another. When many like charges are near one another, they try to get far away from the same charge because charges that are alike tend to repel one another. So when you rub a balloon on your hair, the electrons move to the balloon leaving all positive charges on your hair. Your hair responds by trying to get as far away from the other strands of positively charged hair strands. The result is hair standing straight out from your head. The balloon, being more negative, is able to then “stick” to a dry wall because it is now attracted to the positive charges in the wall. Another demonstration is using magnets showing the student that the positive and negative ends attract, but you cannot get the magnets to stick together with the same charged ends. Using a better model showing an example of particles use the following demonstration: a. Tie a piece of the cereal to one end of a 12 inch piece of thread. Find a place to attach the other end of the thread so that the cereal does not hand close to anything else. (You can tape the thread to the edge of a table but ask permission first.) b. Wash the comb to remove any oils and dry it well. c. Charge the comb by running it through long, dry hair several times, or vigorously rub the comb on a wool sweater. d. Slowly bring the comb near the cereal. It will swing to touch the comb. Hold it still until the cereal jumps away by itself. e. Now try to touch the comb to the cereal again. It will move away as the comb approaches. f. This project can also be done by substituting a balloon for the comb. What Happened: Combing your hair moved electrons from your hair to the comb. The comb had a negative static charge. The neutral cereal was attracted to it. When they touched, electrons slowly moved from the comb to the cereal. Now both objects had the same negative charge, and the cereal was repelled. 3. Discuss with the student by adding different chemicals (coagulant) to the water with the suspended solids it makes more available sites (charged areas) for the particles to stick to which causes the smaller particles to grow and become heavier and settle. Have a beaker of water with some type of suspended solids (dirt). Add a coagulant and start stirring to begin the flocculation process (Alum can be purchased at your local grocer). Once the solids start to floc let settle for a few minutes to show the students how this process works. Note: By visiting your local water treatment facility, the students will be given the opportunity to see firsthand how different water treatment processes work. What Happened: The addition of a coagulant to the water reduces the (usually) negative charge suspended particles which allows them to attract or clump. As the particles get heavier they tend to settle making the treatment process a success. The next step in the process would be filtration if drinking water was being treated. Charged particles repel each other. Uncharged particles are free to collide and aggregate. Another Poster that will be generated for viewing is a water conservation poster illustrating daily use of the common household. Ask students how much water is used in the following common activities. You may want to have them do a math exercise to add the amount of water used in a normal day by a household. Shower = 25 gallons Brushing teeth = 10 gallons Bath tub = 36 gallons Shaving = 20 gallons Dishwashing = 30 gallons Automatic dishwasher = 16 gallons Washing hands = 2 gallons Toilet flushing = 5 to 7 gallons Washing machine = 60 gallons Outdoor watering = 10 gallons per minute Note: The above is an idea for a Sciencefest poster, to give a better understanding on water conservation.