Hands-on Activity: Straining out the Dirt

Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

A photo shows a female health aide using a water filter mounted to the wall in a room.
Students build their own water filters.
copyright
Copyright © 2006 Nyaya Health via Flickr https://www.flickr.com/photos/nyayahealth/6892484355/

Summary

Students groups build water filters using activated carbon, cotton and other materials to clean a "dirty" water sample made from chocolate powder added to tap water. They test and make observations of filter effectiveness, suggesting material and layering design improvements. They see how their filtering process compares to the drinking water treatment processes designed by engineers to provide communities with clean water supplies.

Engineering Connection

Environmental and civil engineers design systems to process communities' water supplies to make them clean enough for people to drink. Depending on the starting water quality, most municipal water treatment systems involve many steps to eliminate the contaminants that could make people sick. Often, the treatment process includes the use of filters of sand and activated carbon to remove particulate matter and certain bacteria just before the water is disinfected with chlorine.

Learning Objectives

After this activity, students should be able to:

  • Design and build a model filter and compare it to processes used by engineers in drinking water treatment.
  • Test and make observations on filter effectiveness.
  • Use data from observations to construct a reasonable explanation of drinking water treatment through a filter.
  • Describe how drinking water filters can help improve the drinking water quality of a community.

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Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • People have made tools to provide food, to make clothing, and to protect themselves. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Technologies can be used to repair damage caused by natural disasters and to break down waste from the use of various products and systems. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Materials List

Each group needs:

  • 0.5 liter (500 ml) plastic water or soda bottle
  • ½ cup granulated activated carbon (GAC); available from chemical supply stores and pet supply stores in the aquarium section
  • 2-3 cotton balls
  • jar, smaller in diameter than the 500 ml bottle so that the water bottle can be supported in the jar without falling through

For entire class to share (and the teacher to use):

  • drill with small diameter bit
  • kitchen knife or scissors
  • 3 teaspoons of chocolate powder mix, such as Hershey's® or Nestle Quik®
  • water, enough water for each bottle to be filled up 3-4 oz.
  • pitcher or bucket, for mixing powdered chocolate and water
  • 4-5 cups of sand
  • 50+ marbles

Introduction/Motivation

How many of you know someone who filters their tap water? How many of you know someone who buys bottled water? Have you ever been in the woods or mountains and drank water from a river after being filtered by a small pump? Why do we do this? Does the water look contaminated? (Answer: Sometimes, yes.) Naturally pure water does not exist. All water sources carry small particles that have been absorbed or dissolved in the water as it passes over river beds, rocks and soil.

In the early 1900s, the U.S. government began requiring specific levels of cleanliness for drinking water. These regulations did not become strict until the Safe Water Drinking Act of 1974, which then underwent changes in 1986 and 1996. This law tells us exactly which drinking water standards our states must meet to provide safe and healthy drinking water to our homes and communities. The U.S. Environmental Protection Agency (EPA) has set standards for more than 80 contaminants that may get into our drinking water and make us sick.

Today, we are going to investigate drinking water filters. We are going to take a sample of muddy water and use the available materials to clean up the water as much as possible. (If available, show students a Pur® filter and ask them if they know what it is composed of; tell them that they will prepare their own Pur® filter for "muddy" water.)

Procedure

Before the Activity

  • With a knife or scissors, cut off and discard the bottoms of each empty 0.5 liter bottle.
  • Using a drill, make two holes in each bottle screw top. Although this step is not required, it slows the water flow, resulting in less mess in the classroom.
  • Prepare a supply of "dirty" water by mixing two or three teaspoons of chocolate powder and the cold water in the pitcher. Don't worry if the powder makes lumps at the top of the mixture.
  • Construct one or two filters as examples and a control. For the control, turn one plastic bottle upside down, with the cut opening to the top, and place a cotton ball in the lid. Screw the lid back onto the bottle. Use this filter as the control filter for students by pouring the mixture into the bottle and watching the chocolate/water mixture pour out. Create another filter or two the same way, but add whatever mixtures of cotton, sand and marbles that you would like to serve as example filters.

With the Students

  1. DIvide the class into groups of four to five students each. Explain to the class that they are going work as if they are environmental engineers designing water filters for a drinking water treatment plant. Their engineering challenge is to make the cleanest water possible out of the provided dirty water sample using any combination of the available materials. One requirement is that each filter must include a cotton ball in the bottle lid.
  2. Have students make predictions on which filter layer will be the most effective at cleaning the water and why.
  3. When each group has finished creating their filters, pour about 2" thick (approximately ½ cup) of granulated activated carbon (GAC) on the top of their layers. Now the filters are ready to be used.
  4. Have students place their filters with the caps downwards on the tops of their glass jars.
  5. Next, the teacher pours the chocolate mixture into the prototype filters for each group. Direct students to observe the "clean" water move from the bottom of the filter into the jar. When the filtration is done, direct students to take their jars and filters to a location where light can illuminate the new mixtures. What happened to the water when it was filtered? (Answer: It turned clearer, less water was remaining, etc.)
  6. Have the class vote on which team's filter cleaned the water the best. As time permits, lead a discussion on why the winning filter was the most effective and ask for suggestions and ideas for how to make the filter even more effective.

Safety Issues

For safety reasons, pre-cut and pre-drill the bottles so students do not handle the knife and drill.

Troubleshooting Tips

If you cannot find granulated activated carbon (GAC) in chemical stores, use carbon for aquarium filters, which is available at pet shops.

Feel free to make available other filter materials for students to use, such as paper towels, coffee filters, fabric, moss, felt and gravel.

Assessment

Pre-Activity Assessment

Know / Want to Know / Learn (KWL) Chart: Before the lesson, ask students to write down in the top left corner of a piece of paper (or as a group on the classroom board), under the title Know, all the things they know about drinking water filters. Next, in the top right corner, under the title Want to Know, ask students to write down anything they want to know about drinking water filters. After the lesson, ask students to list in the bottom half of the page, under the title Learned, all of the things that they have learned about drinking water filters. Ask students to name a few items and write them on the board.

Activity Embedded Assessment

Drawing: Have students draw pictures of their drinking water filters. Require them to sketch and identify the different material layers, indicating as best they can what particles each layer will remove. Point out that this sort of visual documentation and planning is what engineers do when designing new products.

Post-Activity Assessment

Know / Want to Know / Learn (KWL) Chart: Finish the remaining section of the KWL Chart as described in the pre-lesson assessment section. After the lesson, ask students to list in the bottom half of the page, under the title Learned, all of the things that they have learned about drinking water filters. Ask students to name a few items and write them on the board.

Show and Tell: Have teams "show and tell" the filters they created, explaining their work to the rest of the class. Ask students to compare each others' filters and brainstorm other materials and fabrication order that might improve their filters.

Re-Design Practice: If time permits (or as a homework assignment), have students list any design and fabrication changes they would make to improve their filters. If it helps the explanation, have them draw pictures of the new designs. Emphasize that engineers typically re-design products many times before getting a satisfactory solution.

Student-Generated Questions: Have each student come up with one question of their own about filters and/or drinking water to ask the rest of the class. Be prepared to help some students form questions. If the answers are not known by anyone, encourage students to search the U.S. EPA website and report those answers to the class at a later time.

Activity Extensions

Slice open a Pur® (or other type of) filter for students so they can examine its components. Discuss the concept of adsorption—the capability of a solid to attract to its surface molecules of other solid or gaseous materials.

Activity Scaling

For eighth-grade or older students, have each group first filter water using a different individual layer (investigate with sand OR marbles, etc.). Have each team record its observations of that filter type on a group chart on the classroom board. Have teams use these shared research results to inform their own filter designs, referring to them when they explain the logic of the material layers they chose for their final filters. For example, if marbles produce darker filtered water because they let fine particles pass through, while sand does not permit fine particles through, the combination may result in a successful final design approach.

Contributors

Malinda Schaefer; Sharon D. Pérez-Suárez; Matt Lundberg; Ben Heavner; Janet Yowell

Copyright

© 2005 by Regents of the University of Colorado

Supporting Program

Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

Acknowledgements

The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation (GK-12 grant no. 0338326). However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.

Last modified: June 16, 2017

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