Target Grade Level / Age Range:

Grades 9-12


50 minutes


Students will discover how wood chip bioreactors can increase denitrification of excess nitrogen before it leaves fields and enters watersheds.


  • Computers/tablets with internet access – one for every two or three students
  • 4”x6” note cards

Suggested Companion Resources (books and websites)

Vocabulary (with definitions)

  • Bioreactor: an underground trench of wood chips used to remove nitrogen from tile line discharge
  • Tile line: Pipe made of perforated plastic, burned clay, concrete, or similar material, laid below the soil surface to a designed grade and depth, to collect and carry excess water from the soil.
  • Denitrification: the process by which denitrifying bacteria convert some of the nitrates in soil back into nitrogen gas

Background – Agricultural Connections (what would a teacher need to know to be able to teach this content)

A bioreactor is an edge-of-field treatment process which allows the producer to reduce the amount of nitrogen leaving the field from a tile line, improving water quality of the receiving stream. It consists of a buried pit filled with a carbon source, commonly wood chips, through which tile water is diverted. The carbon provides material which serves as a food source for microorganisms. In the low oxygen environment the microbes use the nitrate (NO 3-) to metabolize the carbon, converting the nitrate to harmless atmospheric nitrogen (N 2) gas.

In addition to improved fertilizer management, tillage management, and wetland restoration, bioreactors help improve water quality by reducing nitrate that naturally occurs in agricultural drainage water. Bioreactors can reduce nitrate by an average of 43 percent and have proven to work well in existing filter strips as well as in other locations.

Bioreactors offer a relatively high rate of nitrate removal with a small footprint on the landscape. They require very little maintenance during their lifecycle and a number of programs are available to offset much of the cost.

To date (2016), about 60 bioreactors have been installed in Iowa. It is estimated that Iowa needs roughly 120,000 bioreactors to reach the goals set out in the Iowa Nutrient Reduction Strategy. We need more farmers to try them.

Interest Approach or Motivator

We learned in lesson 3 of this unit that nitrates are water soluble and can be suspended in water. This water can runoff of fields – especially in high precipitation events. We learned in lesson 9 that tile lines can help drain excess water from fields. But how can farmers remove the excess nitrates from the water before they run into watersheds? Have students ponder the question and if they have any ideas to share.

Water treatment facilities for city water supplies can treat water through ion exchange units, reverse osmosis, or distillation. But these processes are costly to build and maintain. They also use input water from a specific identifiable source. Farmers need cheap, low cost solutions. And since water can run off of a farm field in multiple areas, farmers need a solution that can be implemented over large areas of land.


  1. One solution is bioreactors. Share the video (slide #2) as an overview of bioreactors.
  2. Where are bioreactors located? (Slide #3) Break students into teams three. Direct them to computers or tablets with internet access.
    1. Assign each group one of the following watersheds to research.
      1. Beaver Creek Watershed Improvement Plan
      2. Benton-Tama Watershed Improvement Plan   
      3. Lime Creek Watershed Improvement Plan
      4. Lyons Creek Watershed Management Plan
      5. Rock Creek Watershed Plan
      6. Additional bioreactors can be found in the following watersheds. Students can select a watershed of interest, one that is regionally close, or one that is assigned to them. Headwaters Cedar CreekBadger Creek Lake, Holland Creek, West Fork Crooked Creek, and Howard Creek.
    2. Students will read through the watershed plans and will be able to answer the following questions in a short presentation to their peers:
      1. Where is the watershed located? (Name of the watershed and approximate location in relation to cities, rivers, counties, or other landmarks)
      2. Existing bioreactors
      3. Planned bioreactors
      4. Timeline of bioreactor installations
      5. Approximate costs of bioreactor installations.
      6. Key partners
    3. Hint: Because these are extensive documents, students should use keyword searches to find pertinent information. For example, by searching ‘bioreactor’ they can scroll through mentions of bioreactors.
    4. Allow 5 to 10 minutes for the students to conduct their research and answer the questions (slide #4).
    5. Bring the class back together and have each group report out what they learned.

How do bioreactors work?

  1. Hand out copies of these two publications or direct students to the online links:
  2. Students should work with their previous group and prepare to teach a group that had the opposite article. Assign the fact sheet from Iowa State University (red) to one half of the class and the fact sheet from the Iowa Soybean Association (blue) to the other half of the class. Allow 3-5 minutes for students to read their assignment.
  3. Match a red group up with a blue group and instruct red groups to teach what they learned to the blue group. Allow three minutes for this. Then have the groups switch and have blue groups teach what they learned to the red group. Allow three minutes.
  4. Bring the class back together. Present the information on slides 5-7 and ask students to capture key information into their notebooks.
    1. Bioreactors – oldest 1995
    2. 100ft long and 10-30 feet wide
    3. They can drain 20-80 acres
    4. Nitrate reduction is 15-60%
    5. Wood chips may need to be replaced (height of bioreactor will decrease as bacteria eat the wood chips).
    6. Life span is 15-20 years
    7. Route field drainage water through a buried trench filled with woodchips
    8. Bacteria convert nitrate (NO 3-) to atmospheric nitrogen gas (N 2)
    9. Bacteria called denitrifiers
    10. Bacteria breathe nitrate in and breath nitrogen out
    11. Bacteria eat the organic matter – in many cases woodchips
    12. Bacteria are anaerobic (they don’t need oxygen)
    13. Control structures regulate water inflow and outflow
    14. As of 2016, there are 60 bioreactors in Iowa
    15. It is estimated that farmers in Iowa need to install 120,000 to 180,000 bioreactors

Implementation: Have students work with their group to develop a plan and recommendation based on their new-found knowledge to evaluate or refine the watershed plan that they previously reviewed. The plan should make one or two recommendations specific to bioreactors with enough detail that they could present it to the watershed planning and partner group. Groups should write up their proposals and turn them in for grading.

Wrap-up: $10,000 Pyramid

  1. Prior to class, create notecards with pieces of information from the lesson
  2. You’ll need one copy of the set of cards for every group of three.
  3. Suggested fact cards (more can be added):
    1. 1995
    2. 100 ft.
    3. 10-30 feet
    4. 20-80 acres
    5. 15-60%
    6. Wood chips
    7. 15-20 years
    8. Denitrifiers
    9. NO 3-
    10. N 2
    11. Atmospheric nitrogen
    12. Nitrates
    13. Anaerobic
    14. Tile lines
    15. Denitrification
    16. 60 bioreactors
    17. 120,000 to 180,000 bioreactors
  4. Explain roles. For this activity there will be a Player, a Clue Giver, and a Teleprompter. The clue giver and player sit facing each other with the teleprompter standing behind the player, displaying the fact cards one at a time to the clue giver. The clue giver silently reads the fact card, then gives the player clues until he or she guesses the information.
  5. Play the game. The game is played in rounds of sixty seconds each. When the player correctly guesses the information on the card, the teleprompter places the card on the table. The clue giver should not use any word or phrase that is on the card as a clue. If they do, that card is forfeit and goes to the back of the deck. If the player is having difficulty guessing a card, the clue giver or player may ask to pass to the next card. In this case, the card is placed at the back of the deck, to return to later if time allows. After each round, the groups count the player’s correct answers and each group’s score is recorded on a board or flip chart. With each new round, everyone in the group switches roles and the entire deck is shuffled for the new player. Play three rounds to allow each student to play each role once. Should a group get through the entire deck, the cards are shuffled and play continues. Rounds two and three can be no-pass rounds without the ability to pass to the next card.

Essential Files (maps, charts, pictures, or documents)

Did you know? (Ag facts)

  • Approximately 60 bioreactors have been installed in Iowa (as of 2016)
  • It is estimated that Iowa needs 120,000 to 180,000 bioreactors installed
  • Bioreactors can remove 15-60% of nitrates from tile water

Extension Activities (how students can carry this beyond the classroom)

  • Have students attend a watershed planning meeting in their area and report back to the class.


Lesson plan development was funded by the Resource Enhancement and Protection Conservation Education Program (REAP CEP). Resource Enhancement and Protection Program (REAP): Invest in Iowa our outdoors, our heritage, our people. REAP is supported by the state of Iowa, providing funding to public and private partners for natural and cultural resources projects, including water quality, wildlife habitat, soil conservation, parks, trails, historic preservation and more.


Will Fett

Organization Affiliation

Iowa Agriculture Literacy Foundation

National Agriculture Literacy Outcomes

  • T1.9-12.a. Describe how wildlife habitats are created and maintained by farmers/ranchers and why these habitats are important (e.g., promoting pollinator habitat, insect refuges, creating buffer zones for nutrient management, etc.)
  • T1.9-12.b. Describe resource and conservation management practices used in agricultural systems (e.g., riparian management, rotational grazing, no till farming, crop and variety selection, wildlife management, timber harvesting techniques)
  • T1.9-12.f. Evaluate the various definitions of “sustainable agriculture,” considering population growth, carbon footprint, environmental systems, land and water resources, and economics

Iowa Core Standards

  • HS-PS1-1. Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms. (nitrogen cycle and conversion of nitrogen and nitrous oxide to ammonia)
  • HS-LS2-3. Construct and revise an explanation based on evidence for the cycling of matter and flow of energy in aerobic and anaerobic conditions. (bioreactors)
  • HS-ESS2-5. Plan and conduct an investigation of the properties of water and its effects on Earth materials and surface processes. (water cycle, tiling, terracing, bioreactors, riparian areas)
  • HS-ESS3-4. Evaluate or refine a technological solution that reduces impacts of human activities on natural systems. * (bioreactors, buffer strips, terraces, cover crops)

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