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Worksheet Grade 9 Social Studies & Civics

Kirkbourne's Biosolids Ordinance: A Nutrient Loading Worksheet

A grade 9 worksheet using the pounds formula to test whether a fictional town's proposed setback ordinance would end land application of treated biosolids.

Objectives

  1. Students will apply the pounds formula to calculate daily loading from a concentration and a flow.
  2. Students will convert an annual biosolids production into the farm acreage its nitrogen can supply.
  3. Students will evaluate the intended and unintended outcomes of a local setback ordinance.

Vocabulary

Biosolids
Biosolids are the nutrient-rich solid material left over after sewage sludge has been treated and made safe. Many farms use treated biosolids as fertilizer for their fields.

Also: land application, setback, agronomic rate, removal efficiency

Teacher overview

Treated sewage solids can be handled as waste for disposal or used as fertilizer, and a town that spreads them on nearby farmland has chosen the second use. Neighbors who live beside those fields often ask for a setback, which is a required distance between an application field and the nearest home. This worksheet uses the fictional town of Kirkbourne to test whether a proposed setback would actually end the program, using the same loading arithmetic a plant operator uses. The misconception to correct is that a setback ordinance either bans land application or leaves it untouched; the real question is whether the acreage that survives the setback is still larger than the acreage the nitrogen requires, which students calculate here.

Kirkbourne's Biosolids Ordinance: A Nutrient Loading Worksheet — Grade 9 Social Studies & Civics
Name: ____________________________ Date: ______________

Student Worksheet

The town of Kirkbourne, its treatment plant, and every figure below are fictional, written for this worksheet. Kirkbourne's water reclamation facility treats wastewater and sends its treated solids, called biosolids, to farms in nearby Ashglen Township, where they are spread as fertilizer.

Facility and program data:

  • Plant flow: 2.2 MGD.
  • Influent BOD concentration: 240 mg/L. Effluent BOD concentration: 18 mg/L.
  • The pounds formula: loading in pounds per day equals concentration in mg/L times flow in MGD times 8.34.
  • Removal efficiency in percent equals influent minus effluent, divided by influent, times 100.
  • Biosolids production: 1,900 dry pounds per day, every day of the year.
  • One dry ton equals 2,000 dry pounds.
  • The biosolids are 4.0 percent nitrogen by dry weight.
  • Corn in Ashglen Township needs 150 pounds of nitrogen per acre per year.
  • Farmland now enrolled in the program: 620 acres.
  • Under the proposed ordinance, a 500-foot setback from any home would drop enrolled farmland to 430 acres and would cap application at 4 dry tons per acre per year.
  • Landfill disposal, the alternative, would cost Kirkbourne $58 per dry ton.
  1. Use the pounds formula to find the pounds of BOD entering the Kirkbourne plant each day at 240 mg/L and 2.2 MGD. Round to the nearest whole pound.
  2. Use the pounds formula to find the pounds of BOD leaving in the effluent at 18 mg/L and 2.2 MGD. Round to the nearest whole pound.
  3. Using the influent and effluent concentrations, calculate the plant's BOD removal efficiency as a percent.
  4. The plant produces 1,900 dry pounds of biosolids per day. How many dry pounds does it produce in a 365-day year?
  5. Convert your answer from item 4 to dry tons, using 2,000 dry pounds per dry ton.
  6. The biosolids are 4.0 percent nitrogen by dry weight. How many pounds of nitrogen does the year's production contain?
  7. Ashglen Township corn needs 150 pounds of nitrogen per acre per year. How many acres can the year's nitrogen supply at that rate? Round to the nearest tenth of an acre.
  8. The program now uses 620 enrolled acres, and the proposed setback would reduce that to 430 acres. How many acres would the setback remove from the program?
  9. How many acres of margin would remain if the year's nitrogen were applied across the acreage from item 7 and the program kept only the 430 acres allowed under the ordinance?
  10. Spread the year's dry tons from item 5 over the acreage from item 7. What is the application rate in dry tons per acre, rounded to the nearest tenth?
  11. If Kirkbourne could not land-apply at all and sent the year's dry tons from item 5 to a landfill at $58 per dry ton, what would one year cost?
  12. Using your answers to items 9 and 10, explain whether the 500-foot setback would force Kirkbourne to end land application. Support your answer with both numbers.
  13. Residents living near the Ashglen fields proposed the setback. Name one outcome they intended and one outcome they probably did not intend, and explain the second one.

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: 4,404 pounds per day.
    Multiply 240 mg/L by 2.2 MGD by 8.34, which gives 4,403.52 pounds per day and rounds to 4,404 pounds per day at the fictional Kirkbourne plant.
  2. Answer: 330 pounds per day.
    Multiply 18 mg/L by 2.2 MGD by 8.34, which gives 330.26 pounds per day and rounds to 330 pounds per day.
  3. Answer: 92.5 percent.
    Subtract 18 from 240 to get 222, divide by 240 to get 0.925, and multiply by 100.
  4. Answer: 693,500 dry pounds.
    Multiply 1,900 dry pounds per day by 365 days.
  5. Answer: 346.75 dry tons.
    Divide 693,500 dry pounds by 2,000 dry pounds per dry ton.
  6. Answer: 27,740 pounds of nitrogen.
    Multiply 693,500 dry pounds by 0.040, since the biosolids are 4.0 percent nitrogen by dry weight.
  7. Answer: 184.9 acres.
    Divide 27,740 pounds of nitrogen by 150 pounds per acre, which gives 184.93 acres and rounds to 184.9 acres.
  8. Answer: 190 acres.
    Subtract the 430 acres that would remain from the 620 acres enrolled now.
  9. Answer: 245.1 acres.
    Subtract the 184.9 acres the nitrogen requires from the 430 acres the ordinance would leave in the program.
  10. Answer: 1.9 dry tons per acre.
    Divide 346.75 dry tons by 184.9 acres, which gives 1.875 and rounds to 1.9 dry tons per acre.
  11. Answer: $20,111.50.
    Multiply 346.75 dry tons by $58 per dry ton. This is the yearly landfill cost the fictional town would face if the program ended.
  12. Answer: No, the setback would not end land application. Item 9 shows 245.1 acres of margin beyond what the nitrogen requires, and item 10 shows an application rate of 1.9 dry tons per acre, which is well under the ordinance's cap of 4 dry tons per acre. Kirkbourne would lose 190 acres of flexibility and would have to haul farther, yet the program would still fit inside the remaining land.
  13. Answer: The intended outcome is distance between homes and the spreading equipment, which reduces odor complaints and the sense that the nearest neighbors carry the whole burden. An outcome they probably did not intend is concentration: with 190 acres removed, the same tonnage now goes to fewer fields, so the farms that remain in the program receive more frequent applications, and those farms may be closer to a different set of neighbors. Accept other well-supported unintended outcomes, such as longer hauling distances or higher costs that appear later in sewer rates.

Differentiation

Support

Give students a worked pounds-formula example for the fictional Kirkbourne plant using different numbers, such as 200 mg/L at 1.0 MGD, before item 1. Provide a conversion ladder showing dry pounds to dry tons to acres with the arrows labeled, and allow calculators throughout.

Extension

Ask students to find the smallest number of enrolled acres the fictional town of Kirkbourne could keep and still stay under the 4 dry tons per acre cap for the full year's production. They must show the inequality they solved and compare that acreage to the 430 acres the ordinance would leave.

ELL supports

Pre-teach "biosolids," "setback," "agronomic rate," and "removal efficiency" with a simple map of the fictional Ashglen Township fields showing a shaded 500-foot band around each home. Provide sentence frames for items 12 and 13: "The setback would not stop the program because ___ and ___," and "Residents wanted ___, but they may also have caused ___."

Extensions

Students find out how their own state regulates land application of biosolids, using only the state environmental agency's published rule summary, and compare the required setback distance there to the fictional 500-foot setback proposed in Kirkbourne. A second option is to write the two-paragraph staff report the Kirkbourne plant superintendent would send to the town board, stating the calculated margin and recommending a position on the ordinance.