Water for Schools
Menu

Worksheet Grade 11 Careers & CTE

Fenmark Plant Chlorination: An Operator Pounds-Formula Worksheet

A grade 11 careers worksheet where students use the operator pounds formula to find chlorine feed, demand, and flow at a fictional water treatment plant.

Objectives

  1. Students will apply the operator pounds formula to calculate daily chlorine feed from a dose and a flow.
  2. Students will calculate chlorine demand and compare a residual against the regulatory maximum.

Vocabulary

Key words: pounds formula, chlorine dose, chlorine demand, residual

Teacher overview

Setting the chlorine feed is one of the most important calculations a treatment operator makes, and it runs on a single formula. This worksheet uses the fictional Fenmark Water Treatment Plant so students can practice the operator pounds formula the way it appears on a certification exam. The common misconception this worksheet corrects is treating the milligrams-per-liter dose as if it were the pounds-per-day feed; the dose must be multiplied by the flow and by the weight of water first.

Fenmark Plant Chlorination: An Operator Pounds-Formula Worksheet — Grade 11 Careers & CTE
Name: ____________________________ Date: ______________

Student Worksheet

The fictional Fenmark Water Treatment Plant treats a flow of 3.2 MGD. Use these facts for every problem: one gallon of water weighs 8.34 pounds; the pounds formula is pounds per day = concentration (mg/L) × flow (MGD) × 8.34; the chlorine maximum residual disinfectant level (MRDL) is 4.0 mg/L; one MGD equals 694 gpm.

  1. To apply a chlorine dose of 2.5 mg/L to the 3.2 MGD flow, how many pounds of chlorine per day must the operator feed?
  2. After the contact tank, the operator measures a free chlorine residual of 0.8 mg/L. The chlorine demand equals the dose minus the residual. What is the chlorine demand, in mg/L?
  3. How many pounds per day of chlorine were consumed by that demand? Use the demand from item 2, the 3.2 MGD flow, and the pounds formula.
  4. Convert the plant's flow of 3.2 MGD to gallons per minute, using one MGD equals 694 gpm.
  5. The chlorine MRDL is 4.0 mg/L. The finished-water residual is 0.8 mg/L. By how many mg/L is the residual below the MRDL?
  6. On a high-demand day the flow rises to 5.0 MGD and the operator keeps the same 2.5 mg/L dose. How many pounds of chlorine per day are needed now?
  7. Compare items 1 and 6. How many more pounds of chlorine per day does the plant feed at 5.0 MGD than at 3.2 MGD, at the same dose?
  8. Explain why the pounds-per-day of chlorine changes when the flow changes, even though the dose in milligrams per liter stays the same.

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: 66.72 lb/day. Pounds per day = 2.5 mg/L × 3.2 MGD × 8.34 = 66.72 lb/day.
  2. Answer: 1.7 mg/L. Chlorine demand = dose minus residual = 2.5 mg/L − 0.8 mg/L = 1.7 mg/L.
  3. Answer: 45.37 lb/day. Pounds per day = 1.7 mg/L × 3.2 MGD × 8.34 = 45.37 lb/day.
  4. Answer: 2,220.8 gpm. 3.2 MGD × 694 gpm per MGD = 2,220.8 gpm, or about 2,221 gpm.
  5. Answer: 3.2 mg/L. 4.0 mg/L − 0.8 mg/L = 3.2 mg/L below the maximum.
  6. Answer: 104.25 lb/day. Pounds per day = 2.5 mg/L × 5.0 MGD × 8.34 = 104.25 lb/day.
  7. Answer: 37.53 lb/day. 104.25 lb/day − 66.72 lb/day = 37.53 lb/day more at the higher flow.
  8. Answer: The pounds formula multiplies the dose by the flow, so a larger flow carries the same milligrams-per-liter dose through more total gallons each day, which requires feeding more total pounds of chlorine even though the concentration is unchanged.

Differentiation

Support

Provide a worked example with a different flow and dose (for instance, 2.0 mg/L at 1.0 MGD) fully solved with the pounds formula, and give students a printed strip listing the three constants so they do not need to recall them.

Extension

Ask students to work backward: if the operator at the fictional Fenmark plant can feed at most 90 pounds of chlorine per day at the 3.2 MGD flow, what is the highest dose in milligrams per liter the plant can apply? Have them show the rearranged formula.

ELL supports

Pre-teach "dose," "demand," "residual," and "pounds formula" with simple definitions and a labeled arrow diagram (dose in, demand used up, residual left over). Allow item 8 to be answered with a labeled sketch plus a short phrase.