WTO - Water Treatment Operator Water Treatment Math Questions and Answers 1 — Questions and Answers
Question 1: A water treatment plant treats a flow of 7.0 MGD. If the desired dose for sodium hypochlorite is 3.0 mg/L, how many pounds of chemical will be required per day?
- 121.2 lbs/day
- 175.1 lbs/day (Correct answer)
- 21.0 lbs/day
- 1,459.5 lbs/day
Correct answer: 175.1 lbs/day
This calculation uses the 'pounds formula': lbs/day = Flow (MGD) x Dose (mg/L) x 8.34 lbs/gal. Plugging in the given values: 7.0 MGD x 3.0 mg/L x 8.34 lbs/gal = 175.14 lbs/day.
Question 2: A circular clarifier has a diameter of 80 feet and a water depth of 15 feet. If the plant flow is 4.0 MGD, what is the detention time in hours?
- 1.34 hours
- 0.28 hours
- 6.78 hours
- 3.37 hours (Correct answer)
Correct answer: 3.37 hours
First, calculate the volume of the tank in gallons: Volume = 0.785 x Diameter² x Depth x 7.48 gal/ft³. Volume = 0.785 x (80 ft)² x 15 ft x 7.48 gal/ft³ = 563,673.6 gallons. Next, convert the flow rate to gallons per hour: 4,000,000 gal/day ÷ 24 hr/day = 166,667 gal/hr. Finally, calculate detention time: Detention Time = Volume (gal) ÷ Flow Rate (gal/hr) = 563,673.6 gal ÷ 166,667 gal/hr = 3.38 hours.
Question 3: A gravity filter has surface dimensions of 22 feet by 30 feet. If the filter is receiving a flow of 2,300 gallons per minute, what is the filter loading rate?
- 4.21 gpm/ft²
- 2.89 gpm/ft²
- 3.48 gpm/ft² (Correct answer)
- 5.15 gpm/ft²
Correct answer: 3.48 gpm/ft²
First, calculate the surface area of the filter: Area = Length x Width = 22 ft x 30 ft = 660 ft². Next, use the filter loading rate formula: Loading Rate = Flow (gpm) ÷ Surface Area (ft²) = 2,300 gpm ÷ 660 ft² = 3.48 gpm/ft².
Question 4: An operator is calibrating a chemical feed pump. A calibration test shows that the pump delivered 750 mL in 3 minutes. What is the feed rate in gallons per day (gpd)?
- 135.5 gpd
- 26.5 gpd
- 95.1 gpd
- 66.1 gpd (Correct answer)
Correct answer: 66.1 gpd
First, find the rate in mL/min: 750 mL ÷ 3 min = 250 mL/min. Then, convert mL/min to gpd using conversion factors: 250 mL/min x (1 L / 1000 mL) x (1 gal / 3.785 L) x (1440 min / 1 day) = 95.1 gpd. Alternatively, a common conversion factor is mL/min x 0.3804 = gpd. 250 * 0.3804 = 95.1 gpd.
Question 5: A pump must deliver 800 gpm against a total head of 120 feet. What is the required water horsepower (WHP)?
- 24.2 WHP (Correct answer)
- 15.8 WHP
- 31.4 WHP
- 45.0 WHP
Correct answer: 24.2 WHP
The formula for Water Horsepower (WHP) is: WHP = (Flow Rate (gpm) x Total Head (ft)) / 3960. Plugging in the values: (800 gpm x 120 ft) / 3960 = 96,000 / 3960 = 24.24 WHP.
Question 6: A water plant uses 125 pounds of a chemical per day to treat a flow of 3.5 MGD. What is the calculated dosage in mg/L?
- 5.6 mg/L
- 3.1 mg/L
- 4.3 mg/L (Correct answer)
- 2.9 mg/L
Correct answer: 4.3 mg/L
This requires rearranging the 'pounds formula' to solve for dosage: Dose (mg/L) = lbs/day ÷ (Flow (MGD) x 8.34 lbs/gal). Plugging in the values: Dose (mg/L) = 125 lbs/day ÷ (3.5 MGD x 8.34 lbs/gal) = 125 ÷ 29.19 = 4.28 mg/L.
WTO - Water Treatment Operator Water Treatment Math Questions and Answers 1
A water treatment plant treats a flow of 7.0 MGD.
If the desired dose for sodium hypochlorite is 3.0 mg/L, how many pounds of chemical will be required per day?