This activity introduces issues related to sustainability and community planning by focusing on one of earth’s most precious resources: water.
Volunteers will lead a discussion on where their local water comes from and how communities around the country are developing and testing innovative strategies to conserve and use water in sustainable ways. Through this discussion and hands-on activity, students will learn about local water ecology, water quality and relevant engineering applications.
Using a plastic bottle and some other simple elements, you can create a water filter with your students and start a discussion about water quality, as well as other issues related to water and sustainability in the community.
Half or one liter plastic bottle, box cutter, sand, coffee filter, activated carbon (from a pet store), plastic cups, food coloring
Water Filter Construction
- Using a scissor or a box cutter, cut the top off a half or one liter plastic soda bottle, about 3/4 the way up from the base of the bottle.
- Create a "materials" table with sand, rocks, activated carbon and coffee filters.
- Now divide students into design teams or if enough materials are available, have students gather one of each of the following materials: a ˝ cup of sand, a ˝ cup of activated carbon, 1/2 cup of rocks/gravel, string, coffee filter and plastic bottle pieces.
- Next, instruct students to create the main structure of their filter. Invert the top plastic bottle piece to form a funnel into the remaining bottle, which will now serve as a reservoir or basin for water to collect. The top portion will act as a funnel for filtering your sample water.
- Using a coffee filter, instruct students to place this in their makeshift funnel top portion. Now have each team construct layers that will make up their filter.
- Talk to students about their material choices and how each media - sand, carbon and rock - are different “particle sizes” and will therefore influence the kind of filter created. Tell each team to discuss which layering techniques they will use for their filters: sand first? Or rocks first? Encourage students to begin laying down their first layers.
Note: An optimal filter will consist of: first, a 1/2 inch layer of activated carbon, then sand and finally some coarser gravel bits at the top of the filter. This is a gravity fed filtration system using a method of percolation. In this kind of system, particle size is key. A well functioning filter will have larger media (gravel, rocks) and particle sizes on the top of the funnel filtration system with smaller particle sizes (sand and activated carbon) toward the bottom. This allows larger materials like dirt, leaves and other organic matter to be filtered first, allowing water to pass through to the activated carbon layer where naturally charged ions are able to “grab” smaller particles one can only see with a microscope. The coffee filter serves as a final membrane to collect wastewater constituents that have been filtered.
- Now that each group or student has their filters completed, experiment with how effective the designs are.
- In a separate vessel, create some “mock wastewater” to use for your experiment. Add a little bit of food color, some glitter or a bit of soil.
- Now line up each team's water filter. Help students slowly trickle this mock “wastewater” through their filter to see how effective their designs turned out to be. Use a stopwatch to see how fast water trickles through and compare the reservoirs to see how effectively materials were filtered out.
Note: A good result will be a water filter that slowly lets water pass through with larger particles gathered on top and smaller particles caught in the lower levels of the filter system. Most of the food color should be filtered out and the water should look relatively clear. Most modern wastewater treatment systems use similar methods comprised of a large screen to filter large items, then brought down to holding tanks where solids and liquids are separated. Solids are dried and sent to a landfill, and the remaining liquids are pushed through membranes and other media to extract finer particles.
- If time allows, you can use a simple Water Quality Testing kit available at any science education supply store to gauge water quality parameters such as pH, turbidity, dissolved oxygen levels and measure of chlorine.
- Setup a water quality testing station with pipettes and 10 mL test tubes. Instruct students to pour 10 mL of their sample wastewater into their test tubes. Using water quality indicator tablets (again available at any science education store) measure major parameters.
- Determine the water quality of the samples.