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Lesson plan Grade 7 Careers & CTE

Recovering Phosphorus at Dunwick: A Nutrient Career Lesson

A grade 7 careers lesson on the resource recovery technician at a fictional reclamation facility, with percent-removal math and a benefit-and-cost discussion.

Objectives

  1. Students will describe the daily work of a resource recovery technician at a reclamation facility.
  2. Students will calculate percent removal and percent decrease from facility operating data.
  3. Students will explain why a plant treats phosphorus as both a pollutant and a product.

Vocabulary

Effluent
Effluent is the cleaned water that leaves a treatment plant at the end of the process. It is tested carefully before being released to a river, lake, or the ocean.

Also: nutrient recovery, phosphorus, reclamation facility, struvite

Teacher overview

Phosphorus that leaves a wastewater plant can feed algae blooms downstream, yet the same phosphorus is the main ingredient in farm fertilizer. Some plants now run a recovery reactor that pulls phosphorus out of the water as small mineral pellets, and a technician operates that equipment. This lesson introduces that role through the fictional town of Dunwick and asks students to compute percent removal from the facility's records. Students often assume that everything a wastewater plant removes is waste, so the lesson makes the double identity of phosphorus explicit and returns to it in the closing discussion.

Procedure

  1. Hook (5 min): Show students a bag of garden fertilizer or a photograph of one and read the three numbers on the label aloud. Tell them the middle number stands for phosphorus. Ask where a town might find phosphorus if it could not buy any, and take three or four responses without correcting them.

  2. Background (10 min): Explain that the town of Dunwick runs a water reclamation facility, and that phosphorus arrives there every day in what the town sends down its drains. Describe the two problems the facility faced. Phosphorus leaving in the treated water feeds algae in the river. Phosphorus staying inside the plant builds a hard mineral crust in pipes and pumps, which crews then have to cut out. Introduce Mira Lindqvist, the facility's resource recovery technician, and list her daily tasks: checking the reactor's mixing rate, testing the water going in and coming out, adding magnesium on a schedule, drawing off and drying the pellets, and logging every batch. Name the training routes into her job, which include an operator license earned by exam after a high school diploma and on-the-job training, a two-year environmental technology degree, and a four-year degree for staff who move into process design.

  3. Model the math (8 min): Work one percent-removal problem on the board with numbers the students will not see again. Suppose water entering a recovery reactor carries 8 mg/L of phosphorus and water leaving carries 2 mg/L. Show the subtraction first, 8 minus 2, which gives 6. Then divide 6 by the starting value of 8 to get 0.75, and multiply by 100 to get 75 percent. Say plainly that the starting value goes in the denominator, and write that rule where students can see it for the rest of the period.

  4. Formative check (2 min): Ask the whole class one question: if a value falls from 20 to 15, which number belongs in the denominator? Have every student show one finger for 20 and two fingers for 15. If fewer than about four out of five students show one finger, work a second example before releasing them to the handout.

  5. Handout work (15 min): Distribute the student handout and have students work questions 1 through 5 in pairs, then question 6 alone. Circulate and check that students subtract before they divide on questions 1 and 5.

  6. Closing discussion (7 min): Pose the benefit-and-cost question. A recovery reactor costs the town money to buy and to run, while cleaning mineral buildup out of pipes also costs money and takes crews away from other work. Ask students who benefits from the reactor and who pays for it, and record their reasons in two columns on the board.

  7. Exit ticket (3 min): Students write one sentence naming a reason Dunwick calls phosphorus a resource and one sentence naming a reason it calls phosphorus a pollutant. Collect the tickets and sort them into three piles for the next day: both reasons correct, one correct, neither correct.

Recovering Phosphorus at Dunwick: A Nutrient Career Lesson — Grade 7 Careers & CTE
Name: ____________________________ Date: ______________

Student Handout

Suppose the town of Dunwick runs a water reclamation facility with a nutrient recovery reactor. Use the numbers given in each question.

  1. Water entering the recovery reactor carries 6 mg/L of phosphorus, and water leaving carries 1.2 mg/L. What percent of the phosphorus was removed?
  2. The reactor makes 45 pounds of fertilizer pellets on an average day. How many pounds does it make in a 30-day month?
  3. The facility treats 3 million gallons on an average day and recovers 45 pounds of pellets that same day. How many pounds are recovered per million gallons treated?
  4. Secondary treatment rules require a monthly average of 30 mg/L or less for BOD. Dunwick reported a monthly average of 12 mg/L. By how many mg/L is Dunwick below that limit?
  5. Before the reactor was installed, crews cleaned mineral buildup out of pipes 25 times a year. After it was installed, they cleaned 4 times a year. What was the percent decrease in cleanings?
  6. Explain why the facility calls phosphorus both a pollutant and a resource.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: 80 percent. The drop is 6 minus 1.2, which is 4.8. Divide 4.8 by the starting value of 6 to get 0.8, then multiply by 100.
  2. Answer: 1,350 pounds. Multiply 45 pounds per day by 30 days.
  3. Answer: 15 pounds per million gallons. Divide 45 pounds by 3 million gallons.
  4. Answer: 18 mg/L. Subtract 12 from 30.
  5. Answer: 84 percent. The drop is 25 minus 4, which is 21. Divide 21 by the starting value of 25 to get 0.84, then multiply by 100. A student who divides by 4 has used the ending value.
  6. Answer: Accept any answer that names both roles. Sample response: phosphorus is a pollutant because it feeds algae in the river when it leaves in treated water, and it is a resource because the recovered pellets are sold as fertilizer.

Differentiation

Support

Provide questions 1 and 5 with the subtraction step already completed, so students begin at the division and focus on which value belongs in the denominator. Give a filled-in example strip at the top of the handout showing the three steps in order: subtract, divide by the starting value, multiply by one hundred. Allow question 6 to be answered as two labeled phrases rather than sentences.

Extension

Ask students to decide how many years of avoided pipe cleanings would make the reactor worth buying if each cleaning takes a crew a full week. Students state the assumption they are making, show the reasoning, and name one thing the comparison leaves out. Accept any defensible answer that states its assumptions clearly.

ELL supports

Pre-teach "recovery," "pellet," and "buildup" with objects or pictures, including a photo of mineral scale inside a pipe. Provide a word bank for question 6 containing pollutant, resource, algae, river, fertilizer, and sell. Allow students to answer question 6 orally to a partner before writing.

Extensions

Have students design the label for a bag of fertilizer made from recovered pellets. The label must name the source of the phosphorus in plain language, state one benefit for a farmer, and answer one question a buyer might reasonably ask about where the material came from. Students then trade labels and mark which claims their partner could actually support from the lesson.