WTO - Water Treatment Operator Water Treatment Math 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?

Accepted Answer

175.1 lbs/day

Answer

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?

Accepted Answer

3.37 hours

Answer

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?

Accepted Answer

3.48 gpm/ft²

Answer

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)?

Accepted Answer

66.1 gpd

Answer

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)?

Accepted Answer

24.2 WHP

Answer

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.

(WTO) Water Treatment Operator Certification Practice Test

(WTO) Water Treatment Operator Certification Practice Test

WTO - Water Treatment Operator Water Treatment Math Questions and Answers