Level 3 · Advanced sample questions
5 free sample questions on math and calculations for the Level 3 · Advanced wastewater treatment operator exam. Try each one, then open the answer to check your work.
A pump delivers 900 gpm against 80 ft of head. Pump efficiency is 75%, and motor efficiency is 90%. What is the motor electrical input expressed in horsepower?
Answer: C. 26.9 hp
The pump requires 24.2 brake hp at the shaft. Accounting for 90% motor efficiency gives an electrical input equivalent to 26.9 hp. Calculation: (900 × 80) ÷ (3,960 × 0.75 × 0.90) = 26.9 hp.
A single-phase AC circuit supplying a blower operates at 480 volts and 40 amps with a power factor of 0.85. What is the power demand?
Answer: A. 16.32 kW
Multiply volts, amps, and power factor, then convert watts to kW. Calculation: 480 × 40 × 0.85 = 16,320 W = 16.32 kW.
A plant treats 1.0 MGD. The active chemical dose is 4.0 mg/L. The feed solution is 50% active and has a density of 1,200 mg/mL. What feed pump setting is needed?
Answer: D. 17.52 mL/min
The feed rate must account for flow, dose, chemical density, active strength, and minutes per day. Calculation: (1.0 × 4.0 × 3.785 × 1,000,000) ÷ (1,200 × 0.50 × 1,440) = 17.52 mL/min.
A centrifuge feed sludge is 4.0% TS. The cake is 25.0% TS, and the centrate is 0.2% TSS. What is the solids capture?
Answer: B. 95.77%
The calculation corrects both the feed and cake values for solids leaving in the centrate. Calculation: [25.0 × (4.0 − 0.2)] ÷ [4.0 × (25.0 − 0.2)] × 100 = 95.77%.
A DAF thickener receives 6,000 lb of solids per day over 400 ft². What is the solids loading rate?
Answer: C. 15.0 lb/day/ft²
Divide the daily solids load by the thickener surface area. Calculation: 6,000 ÷ 400 = 15.0 lb/day/ft².
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