Removing Pollution from Water ILS September

Transcription

1 Removing Pollution from Water Explore different means of removing pollutants The activity can fill several roles. It can be used in the beginning of the school year to cover the scientific method. It can be used as part of a unit on solubility. Or it can be used as part of the unit on ecosystems. In each case the key vocabulary and lessons differ, though they are all applicable. Kit contents: Coffee Filters, Cotton, Paper Towels, Cups, Rubber Bands, Chalk, Food Coloring, Pitcher, Spoon Vocabulary: Scientific Method: the five steps of the scientific method are: observe and ask questions, form a hypothesis, plan an experiment, conduct an experiment, and draw conclusions and communicate results. Solubility: mixture, solution, solubility, suspension Ecosystem: ecosystem Science Standards: The student knows that different materials are made by physically combining substance and that different objects can be made by combining different materials. (SC.A.1.2.4) The student understands how changes in the environment affect organisms (for example, some organisms move in, others move out; some organisms survive and reproduce, others die). (SC.G ) The student extends and refines knowledge of ways that, through the use of science processes and knowledge, people can solve problems, make decisions, and form new ideas. (SC.H ) Key Knowledge Vocabulary Scientific Method: hypothesis-- A tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation. Solubility: mixture two or more substances that are combined without changing any of them. Example: granola with nuts and raisins, salad solution a kind of mixture where different kinds of matter are mixed completely with each other. Example: salt water solubility the measure of how much of one material will dissolve in another suspension mixture where some particles of one ingredient are suspended, or floating, in another ingredient. Example: fog, orange juice. Ecosystems: [This activity is part of an overview of a couple of chapters dealing with ecosystems and the environment. The vocabulary of the chapters doesn't quite match with this activity, so the vocabulary below is some of the words that will likely come up in this discussion.] watershed--area that drains to a common point estuary--area where fresh and salt water mix aquifer--formation of sediment or rock capable of holding water point source pollution--pollution that can be traced to a single source, such as a discharge pipe nonpoint source pollution--pollution that comes from diffuse sources such as stormwater that collects sediment, nutrients, bacteria, pesticides, heavy metals, oil, and grease. Concepts Scientific Method: 1. Observe and Ask Questions 2. Form a hypothesis. 3. Plan an experiment what variables to change, what to control; procedure to follow; equipment necessary; how to gather and record data 4. Conduct experiment importance of repeating tests 5. Draw conclusions, communicate results Other key ideas with scientific method compare, classify, predict

2 Solubility: How can you tell a mixture is a suspension and not a solution? The particles in a suspension are larger and more unevenly distributed than those of a solution. When light passes through the suspension, the larger suspended particles scatter the light in all directions producing a cloudy appearance. Mixtures can be solids mixed with solid, solids mixed with liquids, liquids in gases, liquids mixed with liquids, or gases mixed with gases. Fog is liquid mixed with gases. Air is a mixture of different gases. Carbonated beverages have a gas dissolved in a liquid. Ecosystems: From this activity, students will likely see that some materials, like the chalk, will come out with filtering, while other things, like the blue food coloring, are water soluble and will not filter out. Instead, they must be removed chemically or biologically. By slowing down the flow of the water, more pollution can be absorbed. (This also plays a role in nature, by allowing bacteria and other creatures time to filter out water soluble stuff.) When we change the environment, by removing wetlands, adding impervious surfaces like parking lots, and similar things, we change the quality of the water and the types of living things our environment can support. Script Idea -- Ecosystems [This activity is different from the previous activities in that it is a bit more open-ended. We altered it a bit from what is written in the lab manual, so you will need to just have the students note their information on regular paper.] What we will learn about today--removing pollution from water!! (The links in parentheses link to sections in the Related Information page that help answer the questions.) Ask students what they know about water. What water is clean, what is dirty? What makes water dirty? (Water Pollution) What is the water quality in the bodies of water near where they live? (Water Quality) Where does our water come from? Where does the water in their local creek/bayou/river/pond/bay come from? (Watershed) Where does the water that comes through their pipes come from? (Water Supply; Cleaning Water for Human Consumption) Where does water go? What happens to the water that goes in the drainage under the sidewalks? What is the role of the settling ponds? What happens when they flush the toilet? (Cleaning discharge from homes) Explain that the first step of making clean water, whether for water to drink or for cleaning water from household usage, is to filter it. Does the type of material used in a water filter affect how clean filtered water becomes? What types of material can they think of to use to filter the water. Prepare/present the dirty water, using one of the methods on the dirty water page. Have each group choose which materials they want to investigate. Allow them to test two different filtering methods, at least, or have the class come up with multiple permutations of the material to have each group choose one. How will they determine if the water they make is clean? Provide the materials in the kit. A proposed procedure is 1. Place a coffee filter (cotton, paper towel) over the top of a cup and secure with a rubber band. 2. Slowly pour the dirty water on the filter. 3. Observe the contents of the filter and the cup. If you made prefiltered samples, then students could compare their samples to the standards. Otherwise, they could compare the multiple methods. Have them note the materials used, the appearance of the filtering material, and the appearance of their water. Students will likely figure out on their own that they probably want to decant the water and let it sit for a little while to let any major solid settle out. What can the students conclude about their water filters? Would they drink the water they made? What about bacteria, acidity, etc? What kind of filters exist in nature? (Wetlands) What should happen to the material still in the filter? (Soild Waste)

3 Related Information Watershed There are several sources of information on water in this area. One is the Northwest Florida Water Management District. They have publications on their site which include a booklet with some interesting information, which is included below: The Pensacola Bay watershed (map) drains almost 7,000 square miles in Florida and southern Alabama through a narrow pass to the Gulf of Mexico. The Pensacola Bay watershed comprises four river systems, the Escambia, Blackwater, East Bay, and Yellow/Shoal rivers, and five estuaries, the Pensacola, Escambia, Blackwater, and East Bay and Santa Rosa Sound. Pensacola Bay Watershed (from Bay Area Resource Council) Only about a third of the watershed is in Florida, where it covers the majority of Escambia, Santa Rosa, Okaloosa, and northwest Walton counties. The area receives an abundant 60 inches, or five feet, average rainfall a year. Some flows directly into rivers and bays; some evaporates. About a third soaks into sandy soils and contributes to baseflow. Studies by the U.S. Environmental Protection Agency found that the Pensacola Bay system could barely absorb natural runoff. One problem is that fine sediments entering the system from point and nonpoint source pollution settle and are retained. Water Supply The Sand and Gravel Aquifer is a vast layer of sandy soils underlying the western panhandle. The limestone Floridan Aquifer is deeply buried and brackish in this region. Instead, the Sand and Gravel Aquifer, ranging from 150 feet deep at the coast to 450 feet inland, is the primary source of ground water for much of the area. About 100 million gallons a day are pumped from the Sand and Gravel Aquifer in Escambia and Santa Rosa counties, mostly for water supply and industrial uses. Water Pollution Pollution in water comes from many sources, such as human and animal waste, industrial discharge, agricultural discharge, and natural processes. Animal waste contributes bacteria that might be harmful to human and animal health. Animal waste and agricultural discharge contain nutrients, like nitrogen and phosphates, that encourage the growth of algae. Human waste, agricultural discharge, and natural processes increase organic matter that bacteria breakdown. When the bacteria eat, they use up the oxygen in the water. Most pollution makes the water cloudy, so fish can't see. Industrial discharge contains chemicals which may be harmful to living things. Cleaning discharge from homes Septic systems Septic tanks take the water that flows out of the pipes of the house. The contents of the water settle into three layes: scum which floats, sludge which sinks, and the middle water layer. That water contains chemicals and bacteria. It flows to the drain field and is slowly filtered through the dirt and gravel.

4 Wastewater treatment plant A wastewater treatment plant is necessary when people live more densely and do not have room for large drain fields. It has several stages to treating the water. The first stage is like the septic tank, letting solids sink and scum float. The second stage uses bacteria to eat the organic matter and nutrients, and then the bacteria settle out. The third stage uses chemicals to clean the water before it is discharged. Solid waste Solid waste, that settles out in the first stage of water treatment, accounts for 3-5% of the water coming in. This material is kept for 20 to 30 days in large, heated and enclosed tanks called 'digesters.' Here, bacteria break down (digest) the material, reducing its volume, odors, and getting rid of organisms that can cause disease. The finished product is mainly sent to landfills, but sometimes can be used as fertilizer Cleaning water for human consumption Water for human consumption usually comes from the cleanest freshwater source accessible. (Areas with primarily salt water must either import water or install costly desalination plants.) To make water suitable for human consumption, the first step is filtering out large debris. To reduce the salt content, soda ash is added to precipitate some salts. The ph is adjusted. Suspended particles are removed through coagulation and flocculation. The resulting particles may be filtered out or allowed to settle out. Disinfection of the water is accomplished with the addition of chlorine or by UV radiation. Fluoride is added to many municipal water systems for dental health. Other treatments occur in various municipalities. Many households purify their water further. Many household water filters use carbon. Boiling water can kill bacteria. Iodine tablets used by campers work similarly to chlorine to disinfect water. Wetlands Wetlands act as natural water purifiers, improving the quality of water, as well as provide other benifits such as floodwater storage, fish and wildlife habitat, aesthetics, and biological productivity. Wetlands function like natural tubs or sponges, storing water and slowly releasing it. This process slows the water s momentum and erosive potential, reduces flood heights, and allows for ground water recharge, which contributes to base flow to surface water systems during dry periods. After being slowed by a wetland, water moves around plants, allowing the suspended sediment to drop out and settle to the wetland floor. Nutrients from fertilizer application, manure, leaking septic tanks, and municipal sewage that are dissolved in the water are often absorbed by plant roots and microorganisms in the soil. Other pollutants stick to soil particles. In many cases, this filtration process removes much of the water s nutrient and pollutant load by the time it leaves a wetland. Water quality A number of bodies of water in our area are not very clean. To get a recent report on the quality of water in monitored areas, visit the Florida Department of Environmental Protection. How filtering methods work Carbon vs. sand. Carbon granules are rough, having many small crevices that can bind small molecules like food coloring. Sand is relatively smooth, so it mostly removes large particles such as dirt. Script Idea focusing on solutions Note: There are many extra demonstrations possible with solubility. Pick and choose which you like, what you have time for. Many could be altered to be experiments of their own, so maybe the teacher can do the official activity and you do another. The materials for the extra demonstrations are not included in the kits. What we will learn about today--mixtures and solutions!! What do the kids know about solutions? What are some different solutions and mixtures you can name? What are the differences between solutions and mixtures? What is a solvent? Do the kids know any good solvents, something in which many things dissolve? They should come up with water. What can they think of that dissolves in water? (Sugar, salt, baking soda, food coloring, marker ink (washable), laundry detergent (in some fashion), bath tub dyes). What doesn't dissolve in water? Let's say you have some dirty water. How can you make it clean? What if it had large debris, like leaves? (scoop them out, filter) What if it had something soluble, like salt or dye? (Distill, freeze, precipitate)

5 Let's explore filtration. What variables might affect the efficacy of the filtration? What types of material can they think of to use to filter the water? Prepare/present the dirty water, using one of the methods on the dirty water page. Have each group choose which materials they want to investigate. Allow them to test two different filtering methods, at least, or have the class come up with multiple permutations of the material to have each group choose one. How will they determine if the water they make is clean? Provide the materials in the kit. A proposed procedure is 1. Place a coffee filter (cotton, paper towel) over the top of a cup and secure with a rubber band. 2. Slowly pour the dirty water on the filter. 3. Observe the contents of the filter and the cup. If you made prefiltered samples, then students could compare their samples to the standards. Otherwise, they could compare the multiple methods. Have them note the materials used, the appearance of the filtering material, and the appearance of their water. What variables affected the filtration? Students will likely figure out on their own that they probably want to decant the water and let it sit for a little while to let any major solid settle out. Also, the more time the water stays in the filtering material, the more that will likely be filtered out. What can the students conclude about their water filters? Would they drink the water they made? Did any of the stuff soluble in water get filtered out? Did any of the insoluble stuff come through their filters? What kind of filters exist in nature? (Wetlands) Related Information - Solutions Drinking water is not pure water but rather has many salts and other compounds in it. These compounds differ by region and water treatment, give a distinctive flavor to tap water. The amount of a compound that can be dissolved varies with temperature and pressure. Once a certain concentration of solute is reached, the solute begins to run into itself more in the solvent, causing it to precipitate out. At that point it is a saturated solution. Distillation is the evaporation of a liquid, followed by condensation. If the original solution is a combination of a liquid and a solid, then this will result in a virtually complete separation. However, if it is two volatile liquids, it is a little harder. Both liquids will enter the vapor phase, though the one with the lower boiling point will be present in greater amounts in the vapor. This is how the distill crude oil into grades (supreme, regular, small volatiles like toluene, tar) and alcohol. How filtering methods work Carbon vs. sand. Carbon granules are rough, having many small crevices that can bind small molecules like food coloring. Sand is relatively smooth, so it mostly removes large particles such as dirt. Emulsion Demonstration Materials plastic cup water 4 glass jars with tight lids vinegar vegetable oil food color Procedure: Part 1: Add the food color to the water in a plastic cup. teaspoon dish soap egg Add a few drops of the colored water to the oil in a glass jar. What do the students observe? The water should form a nearly perfect sphere, then sink to the bottom. Add a few drops more. Can you get the oil and water to mix? What can you try?

6 Screw the lid onto the jar. Give one hard shake. What do the students observe? What happens if you let the jar rest? Does all of the water eventually get to the bottom? (There likely are a few tiny drops near the top. They are so small that the buoyant force of the oil is keeping them afloat.) So, if the tiny drops stay suspended, what if we make the water into very tiny droplets. Shake the jar vigorously for several minutes. What do you observe? Does the water take longer to settle out? This is called a suspension of water in oil. Part 2: What ideas do the students have for how to get the oil and water to stay together, to get the oil to go into solution in the water? Combine equal amounts (approximately a quarter cup) of oil and water in two small jars. To one add one teaspoon of detergent. Have 2 students shake the jars hard about 5 times. Measure how long it takes the oil and water to separate in each. The better the detergent, the longer the oil and water stay as an emulsion. How does soap work? It has two side, one that likes water and one that likes oil. Imagine 2 kids who had a big fight. They may not talk to each other, but there may be a 3 rd kid who both still like who can mediate the dispute. Soap can form a protective ball around an oil droplet, and this circle can stay dissolved in the water. emulsion: A suspension of small globules of one liquid in a second liquid with which the first will not mix Students could try this at home with a variety of household products to compare how long they stay in an emulsion. What happened? Detergents have a hydrophilic (water loving) head and a hydrophobic (oil attracting) tail. There are other effects, too, such as lowering the surface tension of water. Different detergents are designed for different tasks such as removing dirt, oil, crayons, so they have slightly different abilities to dissolve the oil in the water. Part 3: How many kids have cooked? Do they ever mix oil (or butter) and water in a recipe? Some places might include boxed brownies, cake mix, cookies (butter and vanilla extract). What makes it so the oil and water can mix in these recipes? Mix 1/4 cup oil, 1/4 cup vinegar in a jar. Shake well for 3-4 minutes, let stand 3-4 minutes. Observe. Add 1 egg yolk to the jar. Shake well for 3-4 minutes. Observe. What happened? The egg yolk has a chemical called lecithin which is a lot like soap. Many commercial foods have lecithin instead of a regular egg. Lecithin can be purified out of eggs or soybeans and stored for a long time without refrigeration. Alternatively, lecithin is also synthesized in a laboratory, typically from petroleum derived products. Lecithin is a key building block of cell membranes it is found in every cell in your body. What the students will learn from this experiment: Some materials will not dissolve in or even mix with others. A third material may be able to make the two others mix together, at least for a short time. Dissolving Polymers Demonstration Materials: 2 styrofoam cups water acetone (available from hardware stores, or can use nail polish remover--nail polish isn't as dramatic. Contact Megan Pratt if you would like some acetone from her large jar) packing peanuts both the styrofoam and cellulose kinds pie pan or other container 2 glasses Procedure: Put one styrofoam cup in the pie pan. Pour water into the cup out of the pie pan, acetone into the one into the pie pan. Watch what happens. What do the students observe? The styrofoam cup doesn t disappear, it just dissolves into the acetone. Styrofoam is made of lots of air, so as it dissolves, it shrinks.

7 Styrofoam does not dissolve in water or biological systems. Therefore, it just fills landfills. Even when it is recycled, it can not be used to make cups again because of impurities introduced. Therefore it becomes fillers or other things that can t be recycled. Chemists have been trying to create a biodegradable type of styrofoam. Hence the new-fangled packing peanuts. Put water in 1 glass, acetone in the other. Add styrofoam pellets to the water and a cellulose pellet to the acetone.observe what happens. Reverse the pellets. Observe. What would happen if we made cups out of cellulose? What the students should learn: There are many kinds of solvents. Some things are soluble in one solvent and not in another. Sometimes we choose a material based on whether it will dissolve in another or not. Footnote: Why does cooking oil not dissolve styrofoam, acetone not dissolve plastic cups? It can be explained by like dissolves like. However, we have to understand that there are more nuances to chemical structure than polar, i.e., water, and nonpolar, oil. The actual chemical structure is critical to determining if a chemical can dissolve another. The styrofoam does not technically dissolve in acetone; the acetone merely softens it, like cooked pasta. When soft, the styrofoam releases the air that was blown into it. Many web sites say acetone dissolves styrofoam, however. The goop left at the end is a clue that it isn t really dissolving.. Acetone is water soluble. Another interesting thing that you could show the kids. Iron in Cereal Although Cheerios O's may look uniform, it is possible to separate out parts of the mixture. Many cereals are fortified with iron, which can be separated out with a strong magnet. Materials 2 cups iron-fortified cereal (Cheerios works, Total has more iron per serving) water large Ziploc bag strong magnet (easiest with a very strong magnet--contact Megan Pratt if you would like to borrow one) Procedure Before the class: Put the cereal in the bag. Add water to about half full. Mash cereal to get it into small pieces. (This could be done in a blender.) At the school: Put the magnet on a table. Gently swish the contents of the bag around on top of the magnet for 30 seconds, being careful not to pull the plastic off the magnet. Flip the bag and magnet over, still making sure not to pull the magnet from the plastic. Gently lift the magnet at an angle, so that the iron filings gather at one end. You can move the filings around by slowly moving the magnet. Other examples online include just grinding up Total and pulling out the filings. What the students will learn from this experiment: This is an example of a solid mixed with a solid. Though cereal may look like one thing, there are a lot of elements that are too small to see. Using a magnet is a method of getting something out of a mixture. Background: The amount of iron in your body is enough to make two small nails. The iron in cereal is elemental iron, just like in nails. You need iron in your diet to make hemoglobin, the protein that carries oxygen in your blood. There is debate whether the iron in the cereal is in your body long enough to be converted into a form that your body can use. Making polluted water You have several choices for making your dirty water. The first uses material provided in the kit. You could have the students make the dirty water or do it for the whole class: 1. Fill pitcher with water and add food coloring. (to show that the water was clear) 2. Pour enough colored water to fill one cup half full. 3. Crush the chalk on a paper towel. 4. Add ½ spoonful of crushed chalk to the colored water.

8 Other ideas include going to a body of water near your school and getting a bucket. Another is to premix a bunch of things, like sand, soil, chalk, food color, or some of the other things below. If you choose this option, you could prefilter a few samples using a few different methods as the water quality "standards".. A third way to make dirty water is to involve the kids in making it. Give each kid a baggy or dixie cup of a "pollutant". Some pollutants could include: wood shavings--beaver sand--river crushed shells--shellfish corn starch--farmer's fertilizer soil--animal manure molasses--human waste water vegetable oil--motorboat fuel and oil paper--litter styrofoam--litter food coloring--litter dish soap--laundromat water soil--construction runoff kool-aid--paint and turpentine vinegar--cars corn syrup with food coloring--factories baking soda--household cleaning Start with a bucket of water. Have each child add their materials. Start with the more natural ones, like the wood chips through shells. Then ask the kids if they would drink the water, eat fish from the water, swim in the water. Then add a few more, asking the same questions frequently. Other Ideas Consider bringing funnels for each group. Or use poke a hole in a styrofoam cup to serve as the funnel. Augment the filtering options with sand, dirt, gravel, pebbles. (Perhaps compare natural filtering with man-made.) Bring a Brita filter or other kind to cut open. Let the students use the carbon in their filters. Provide each group a different "pollutant" to remove. Some might be given water-soluble things and others things that will definitely be trapped in the filter.