After students have done activities related to pure substances and mixtures, students will use their knowledge of properties, boiling points and separation to clean contaminated water to produce pure water. Students should understand that mixtures are two or more substances that are combined, but keep their individual properties. This is the key to primary treatment in wastewater. If you have the equipment to do simple distillations, the students can separate the soluble substances from the water to get pure water. If not, it is a good lesson related to the challenges of real water treatment, where few soluble substances can be removed.

Each substance in the water represents substances commonly found in municipal wastewater. Since all the substances have different properties, they are challenged to remove each substance with a different technique based on the substance. Each substance has to come out clean and clear of the others, so it takes experimentation to find the best order to accomplish this. Here is a list of the best ways to remove each and the order that works well.

• Plastic beads - They float, so a spoon can be used to scoop them off the top of the water
• BB’s - A magnet is swirled through water until all have been attached and removed.
• Pieces of paper towel - Water is stirred, raising the paper off the bottom into the water and they can be caught by the spoon.
• Rice- rice and sand are poured onto the screen. Sand that does not fall through can be rinsed through cleaning the rice
• Sand - A coffee filter removes the sand from the water
• Salt - (if able) distillation separates the salt from the water.

Materials

1. Teacher
2. Powerpoint Slides
3. 1 pipette
4. 1 small aluminum pan (or similar to test a sample of the water)
5. Assemble the following for each group
6. 2 250 ml beaker
7. 1 5x5 square of window screen (large debris filtration)
8. 1 Coffee filter (small debris filtration)
9. 1 magnet
10. 1 spoon
11. Amounts of the following do not not have to be precise
12. Sand (represents insoluble inorganics such as dirt and rock)
13. Salt (represents soluble substances)
14. Plastic beads (represents plastics)
15. Paper towels (represents wipes)
16. BB’s (represents metals)
17. Rice (represents insoluble organics)

If distillation is possible:

1. 1 10 ml beaker
2. 1 50 ml graduated cylinder
3. 1 hot plate
4. 1 large rubber stopper
5. 1 3x3 piece of aluminum foil
6. 1 pair of test tube tongs
7. Student
8. Project Packet

The Plan

1. Time needed: 3 periods
2. Prepare the beakers of contaminated water making sure there is some of each contamination in each beaker of water
3. Introduce the project to students by giving them the packet and helping them understand the criteria and constraints of the project.
4. Show them the powerpoint slides as needed.
5. Let the students experiment and with the order and struggle with the techniques