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Worksheet Grade 9 Careers & CTE

Stoneharrow Resource Recovery: A Biosolids Technician's Log

A grade 9 careers worksheet where students complete a fictional facility's biosolids log: dry tons, hauling, nitrogen application acres, and permit recordkeeping.

Objectives

  1. Students will convert a daily sludge volume into dry tons and wet tons using percent solids.
  2. Students will calculate the land area a facility's biosolids nitrogen requires at a stated crop rate.
  3. Students will audit a land application record against the entries a permit requires.

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: percent solids, dry ton, plant-available nitrogen, agronomic rate, certified applicator

Teacher overview

A water resource recovery facility produces treated effluent and a stream of solids. The solids removed from wastewater are digested, dewatered, and then either landfilled or applied to farmland as a nutrient source, and the technician who manages that stream keeps a log the state reads during an inspection. This worksheet has students complete one day of that log at the fictional Stoneharrow Water Resource Recovery Facility, then audit the application record the permit requires. The error this worksheet is built to catch is treating wet tons and dry tons as the same quantity. Students size the hauling from the dry weight, or the farmland from the wet weight, and end up ordering less than one-fifth of the trucks they need. Percent solids is the number that separates the two, and every item below depends on using it in the right direction.

Stoneharrow Resource Recovery: A Biosolids Technician's Log — Grade 9 Careers & CTE
Name: ____________________________ Date: ______________

Student Worksheet

You are the biosolids technician at the fictional Stoneharrow Water Resource Recovery Facility. Use the facility's data below for every item, and write the unit beside each number you calculate. Round to one decimal place unless the item says otherwise.

  • Digested sludge is pumped to the belt press at 42,000 gallons per day, measured at 2.5 percent solids.
  • One gallon of sludge weighs 8.34 pounds.
  • The cake leaving the belt press measures 18 percent solids.
  • One ton is 2,000 pounds.
  • Stoneharrow's most recent nutrient analysis reports 38 pounds of plant-available nitrogen per dry ton of biosolids.
  • The farm receiving the biosolids grows corn and its nutrient plan calls for 150 pounds of nitrogen per acre.
  • Each hauling truck carries 22 wet tons.
  • Stoneharrow's permit requires six entries on every land application record: the date, the field identification, the wet tons applied, the percent solids, the date of the nutrient analysis, and the certified applicator's signature. The nutrient analysis must be less than 12 months old on the day of application.
  1. Stoneharrow pumps 42,000 gallons of sludge per day at 8.34 pounds per gallon and 2.5 percent solids. Calculate the pounds of dry solids produced each day.
  2. A facility produces 8,757 pounds of dry solids per day, and one ton is 2,000 pounds. Calculate the dry tons produced each day.
  3. The cake leaving the press is 18 percent solids and contains 8,757 pounds of dry solids. Calculate the wet tons of cake produced each day.
  4. Stoneharrow produces 24.3 wet tons of cake per day. Calculate the wet tons produced in a seven-day week.
  5. A week's production is 170.1 wet tons and each truck carries 22 wet tons. Calculate the number of truckloads that week's production fills.
  6. Stoneharrow produces 4.4 dry tons per day, and its biosolids test at 38 pounds of plant-available nitrogen per dry ton. Calculate the pounds of plant-available nitrogen produced each day.
  7. One day's biosolids carry 167.2 pounds of plant-available nitrogen, and the corn nutrient plan calls for 150 pounds of nitrogen per acre. Calculate the acres that one day's production would cover.
  8. Stoneharrow produces 167.2 pounds of plant-available nitrogen per day and operates 365 days a year. At 150 pounds of nitrogen per acre, calculate the acres of corn ground the facility's biosolids would require in a year.
  9. Sludge enters the press at 2.5 percent solids and leaves at 18 percent solids. Calculate how many times more concentrated the cake is than the sludge entering the press.
  10. Each day 350,280 pounds of sludge enters the belt press and 48,650 pounds of cake leaves it. Calculate the pounds of water the press removes each day.
  11. Today is the day of application, and the most recent nutrient analysis on file is dated 14 months ago. The permit requires an analysis less than 12 months old. State whether the biosolids may be applied today.
  12. An application record shows the date, the field identification, the wet tons applied, and the percent solids. Using the six entries the permit requires, state what is missing from the record.
  13. A farmer asks Stoneharrow to apply biosolids to a field whose soil test already shows high phosphorus. Biosolids supply both nitrogen and phosphorus. State which nutrient should set the application rate on that field, and explain your reasoning in two or three sentences.

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: 8,757 lbs.
    Multiply the volume by the weight of a gallon, then by the solids fraction. First, 42,000 gallons times 8.34 pounds per gallon equals 350,280 pounds of sludge. Then 350,280 pounds times 0.025 equals 8,757 pounds of dry solids per day.
  2. Answer: 4.4 dry tons.
    Divide the pounds by the pounds in a ton: 8,757 pounds divided by 2,000 pounds per ton equals 4.3785, which rounds to 4.4 dry tons per day.
  3. Answer: 24.3 wet tons.
    The cake is 18 percent solids, so divide the dry weight by that fraction: 8,757 pounds divided by 0.18 equals 48,650 pounds of cake. Then 48,650 pounds divided by 2,000 pounds per ton equals 24.325, which rounds to 24.3 wet tons per day.
  4. Answer: 170.1 wet tons.
    Multiply the daily production by seven days: 24.3 wet tons times 7 equals 170.1 wet tons per week.
  5. Answer: 7.7 truckloads.
    Divide the weekly tonnage by the truck capacity: 170.1 wet tons divided by 22 wet tons per truck equals 7.73, which rounds to 7.7 truckloads. Because a truck cannot make part of a trip, the hauling schedule would be written for eight trips.
  6. Answer: 167.2 lbs.
    Multiply the dry tons by the nitrogen content: 4.4 dry tons times 38 pounds of plant-available nitrogen per dry ton equals 167.2 pounds per day.
  7. Answer: 1.1 acres.
    Divide the nitrogen available by the nitrogen the crop plan calls for: 167.2 pounds divided by 150 pounds per acre equals 1.11, which rounds to 1.1 acres.
  8. Answer: 406.9 acres.
    Multiply the daily nitrogen by the operating days: 167.2 pounds times 365 days equals 61,028 pounds per year. Then divide by the crop rate: 61,028 pounds divided by 150 pounds per acre equals 406.85, which rounds to 406.9 acres.
  9. Answer: 7.2 times.
    Divide the higher percent solids by the lower: 18 divided by 2.5 equals 7.2, so the cake is 7.2 times as concentrated as the sludge entering the press.
  10. Answer: 301,630 lbs.
    Subtract the cake weight from the sludge weight: 350,280 pounds minus 48,650 pounds equals 301,630 pounds of water removed each day.
  11. Answer: No.
    An analysis dated 14 months ago is older than the 12-month limit the permit sets, so the biosolids may not be applied until a current analysis is on file. The technician would pull a fresh sample and hold the load.
  12. Answer: The nutrient analysis date and the certified applicator's signature.
    The record shows four of the six required entries. The date of the nutrient analysis and the certified applicator's signature are both absent, and an inspector reading this record could not confirm that the material was current or that a certified person applied it.
  13. Answer: Phosphorus.
    Nitrogen usually sets the application rate, but on a field already high in phosphorus, applying enough biosolids to meet the corn's nitrogen need would add far more phosphorus than the soil can hold. The excess moves with runoff into surface water, so on this field the rate is set by phosphorus and the farmer makes up the remaining nitrogen from another source.

Differentiation

Support

Give these students a conversion ladder showing the path from gallons to pounds to dry tons to wet tons, with one worked example at each step from the fictional Stoneharrow data. Complete item 1 together as a class, writing the units into the multiplication. Allow items 11, 12, and 13 to be answered first, since they test the permit rules rather than the arithmetic.

Extension

Ask these students to recalculate items 1 through 3 for a day when the belt press runs poorly and the cake leaves at 15 percent solids rather than 18. Then have them state how many more truckloads that week would require and write the two-sentence note the fictional Stoneharrow technician would send the hauling contractor. Finish by asking what the facility would inspect first when percent solids falls.

ELL supports

Pre-teach biosolids, percent solids, dry ton, wet ton, agronomic rate, and certified applicator with a simple flow diagram of the fictional Stoneharrow process, moving from digester to belt press to truck to field. Provide a labeled pair of jars as a model, one of watery mud standing in for thin sludge and one of stiff clay standing in for cake (never real sludge), so the percent solids difference is visible before it is calculated. Offer a sentence frame for items 11 through 13: "The permit says ___, the record shows ___, so the technician must ___."

Extensions

Have students find the biosolids management page of any nearby wastewater utility and note which of the fictional Stoneharrow quantities that utility also publishes, such as dry tons per year or acres under agreement. Comparing a real facility's published figures against the worksheet shows how much of a technician's log eventually becomes a public record.