Hands-on Activity: Washing Air

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

An illustration of a wet scrubber.
Students observe a simple wet scrubber model
copyright
Copyright © Wikimedia Commons http://upload.wikimedia.org/wikipedia/commons/6/61/Wet_scrubber.jpg

Summary

Students observe and discuss a simple model of a wet scrubber to understand how this pollutant recovery method functions in cleaning industrial air pollution.
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

One of the biggest challenges environmental engineers face is devising new techniques to prevent industrial air pollution. Engineers are creative in designing modern pollutant recovery methods and industrial technologies that clean up and prevent air pollution. Scrubbers are designed for use at power plants and facilities that emit sulfur dioxides and hydrogen sulfide gases. Engineers also design cleaning products that scrub stains from your tub and shower, and non-toxic technologies that clean your oven.

Pre-Req Knowledge

A basic understanding of air pollution.

Learning Objectives

A diagram shows polluted air passing through a layer of steam. Large particles are trapped inside steam droplets. The polluted steam droplets are collected in a filter. Clean air is released.
Figure 1. How a wet scrubber cleans polluted air.
copyright
Copyright © Natalie Mach, Graduate Fellow, Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder, 2004.

After this activity, students should be able to:

  • Describe and explain how a wet scrubber works as a pollutant recovery method.
  • Give examples indicating when the use of a wet scrubber is appropriate.
  • Describe how engineers create technology to help industry clean up their air pollution.
  • Use their knowledge of percentages to understand technological efficiency.

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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.

  • Obtain and combine information about ways individual communities use science ideas to protect the Earth's resources and environment. (Grade 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Waste must be appropriately recycled or disposed of to prevent unnecessary harm to the environment. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Develop, communicate, and justify a procedure to separate simple mixtures based on physical properties (Grade 5) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Materials List

For the class demonstration:

  • Duct tape
  • 1/2 cup chalk dust or fireplace ash
  • 3 clear, glass bottles (such as large olive oil or liquor bottles)
  • 3 rubber corks with 2 holes drilled in each (the corks must fit snuggly into the bottle openings; available at hardware stores, sometimes predrilled)
  • 5 barb connectors (to connect plastic tubing to corks; the connector must fit snuggly into the holes in the corks; available at hardware stores; see Figure 3)
  • 5 ft. clear plastic tubing (the tubing must fit snuggly over the barb connectors; available at hardware stores; see Figure 3)
  • Various pipe connectors, as needed, to transition the narrow tubing to the wider vacuum cleaner nozzle (see Figure 2)
  • Water
  • Paper towels
  • Wet/dry shop vacuum cleaner

A photograph of clear plastic tubing run into metal fittings that cap the end of a vacuum cleaner hose. Duct tape provides additional sealing.
Figure 2. For the class demonstration, make an airtight transition from the narrow tubing to the vacuum cleaner hose.
copyright
Copyright © Sharon Perez, Graduate Fellow, Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder, 2003.

Introduction/Motivation

One of the biggest challenges environmental engineers face is devising new techniques to prevent additional air pollution. Industry is a large contributor to air pollution. Have you ever seen a big factory releasing dark smoke into the air? How does it smell? Sometimes, it does not smell so great! The first type of technology (or pollutant recovery method) we are going to examine is a wet scrubber. A wet scrubber uses water to clean pollutants out of the air.

Scrubbers are used at coal burning power plants, asphalt/concrete plants, and a variety of other facilities that emit sulfur dioxides, hydrogen sulfide and gases with high water solubility. Inside a wet scrubber, solid particles and gases are trapped as they pass through a fine water mist (refer to Figure 1 or the attached How a Wet Scrubber Cleans Polluted Air Diagram). Sometimes the mist is injected with limestone powder to help extract the dirt particles. Wet scrubbers are often used for corrosive, acidic or basic gas streams. The resulting pollutant-laden wastewater is processed into sludge, which is used to make bricks.

How well do you think this works? Today, we are going to model the wet scrubber technology in class.

Procedure

Before the Activity

  • Gather materials and set up the apparatus as shown in Figures 3 and 4. Refer to the Wet Scrubber Model Photo Collection (attachment) for more details.
  • Test the activity at least once before presenting it as a class demonstration.

Photograph showing three bottles connected by hoses.
Figure 3. Experiment setup: A model wet scrubber. Left to right, bottle 1, 2, 3.
copyright
Copyright © Sharon Perez, Graduate Fellow, Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder, 2003.

One photograph shows "in" and "out" labeled tubes for bottles 1, 2 and 3. The other photograph exact placement of a "in" and "out" tubes in one bottle.
Figure 4. Label the tubes for set up of the wet scrubber model. Place the "in" tubes below the water line and the "out" tubes above the water line. Use duct tape to completely seal the connections.
copyright
Copyright © Sharon Perez, Graduate Fellow, Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder, 2003.

With the Students

  1. As a class, brainstorm different ways that water could be used to clean the air. List ideas on the chalkboard.
  2. Put chalk dust or fireplace ash (representing pollution) in the first bottle.
  3. Fill bottle 2 and bottle 3 both 1/3 full of water.
  4. Make sure the "in" tube in each bottle is submerged in the water, while the "out" tube is not.
  5. Connect the "out" tube of bottle 3 to the shop vacuum cleaner. Use the other pipe connectors (see Figure 2) to make a tight connection from the narrow tube to the larger vacuum cleaner tube. Use duct tape to make all the connections airtight.
  6. When ready to start, shake bottle 1 to create the polluted air and turn on the vacuum cleaner at a low setting.
  7. What should happen: Polluted/dirty air in bottle 1 is suctioned into the water in bottle 2. The bottle 2 water cleans the particulates from the air while the cleaner air is suctioned on into bottle 3. Dust may collect in the air above the water in bottle 2. This is why there is a third bottle. The air is cleaned a second time in bottle 3 before being suctioned out by the vacuum cleaner as clean air released into the environment.
  8. Have students record their observations. Tell them to write down anything that strikes them as important.
  9. Discuss the student observations. Explain that a wet scrubber collects not only particulate matter but also captures waste gases. Discuss that the white plume you see coming from a smokestack of a factory may really be (unpolluted) steam coming from a water scrubber.
  10. In conclusion, ask the students the following questions, and discuss as a class:
  • Why does the water in the wet-scrubber change color? (Answer: Visible air pollution [particulate matter] moves from the air into the water.)
  • What does the scrubber filter out of the air? What does it not filter out? (Answer: It filters out fine particulate matter and waste gases. It does not filter out heavy particles of dirt and sludge.)
  • Suggest ways to dispose of the pollutants that are now trapped in the water. (Possible answer: The resulting pollutant-laden wastewater is processed into sludge, which is used to make bricks.)
  • Does the wet scrubber remove all of the particulates? (Answer: The average efficiency of a wet scrubber is about 94%. That means that if there are 100 particulates, 94 of them are caught and six of them make it back into the air.)
  • Is this a good or bad efficiency rate? (Opinions may vary. 94% still means that 6% of the particulates are returning to the atmosphere.)

Attachments

Safety Issues

  • Only draw air through the tubing using a vacuum cleaner; using your mouth may cause accidental inhaling of the contaminated air.

Troubleshooting Tips

The corks, tubing and connectors can be purchased at a hardware store. It is possible to find the corks with predrilled holes.

Make sure that all the connections are tightly sealed with duct tape.

If you are using fireplace ash, replenish it frequently because only the light "floaty" particulates are pulled through the scrubber by the vacuum; the heavier charcoal pieces are not useful for the demonstration.

It is strongly recommended that you practice this demonstration at least once before presenting it to the students.

Assessment

Pre-Activity Assessment

Brainstorming: As a class, have the students engage in open discussion. Remind students that in brainstorming, no idea or suggestion is "silly." All ideas should be respectfully heard. Take an uncritical position, encourage wild ideas and discourage criticism of ideas. Have them raise their hands to respond. Write their ideas on the board. Ask the students:

  • How can water be used to clean the air?

Activity Embedded Assessment

Observations: Ask students to pay close attention and record their observations of the experiment, explaining to them that this is what real scientists and engineers do. Instruct them to record anything that seems important.

Post-Activity Assessment

Observations: Discuss student observations.

Drawing/Journaling: Depending on the students' age, have them draw a picture or write in their own words a description of how a wet scrubber works to clean polluted air. Ask for volunteers to share their descriptions with the class.

Activity Extensions

A wet scrubber's resulting pollutant-laden wastewater is sometimes processed into sludge, which is used to make bricks. How does this work? Have students investigate this process on the Internet (search: sludge dryers, dewatering sludge) and report back to class. Is this a successful pollutant recovery process?

Find local examples of wet scrubbers and arrange a field trip. What pollutants does this wet scrubber remove? What do they do with the wet scrubber wastewater?

Activity Scaling

  • While the demonstration is appropriate for any age level, younger students may have difficulty understanding some of the ways the scrubber functions. Tailor the explanation and discussion to fit the comprehension level of your students.
  • For upper grades, add a math component. Give students a number of particulates, and have them calculate how many are cleaned from the air using a wet scrubber with 94% efficiency. For example, if 100,000 particulates went through this wet scrubber, about 100,000 x .94 = 94,000 would be removed, and 6,000 would remain.

References

Foresman, Scott. Science Insights – Exploring Matter and Energy. Reading, MA: Addison Wesley, 1999.

Markle, Sandra. The Kids' Earth Handbook. Atheneum, NY: John Wiley & Sons, Inc, 1991.

Contributors

Amy Kolenbrander; Sharon Perez; Janet Yowell; Natalie Mach; Malinda Schaefer Zarske; Denise Carlson

Copyright

© 2004 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 a grant 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: July 20, 2017

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