Level 1 · Entry sample questions
5 free sample questions on disinfection for the Level 1 · Entry wastewater treatment operator exam. Try each one, then open the answer to check your work.
An outlet chlorine analyzer suddenly reads 0.0 mg/L. The feed pump indicates its normal rate, and an immediate calibrated grab test reads 1.2 mg/L. What should the operator check first?
Answer: B. Check the sample line
The 1.2 mg/L calibrated grab result shows chlorine is present, so the analyzer sample line is the most direct first check. Raising feed or lowering basin flow could overdose the water, and restarting the sludge rake does not explain the analyzer disagreement.
Channel flow doubles, but the UV system's commanded dose does not change. Lamp power, UV transmittance, and channel level remain normal. What should the operator check first?
Answer: D. UV flow input
The commanded dose should respond when channel flow doubles, so the UV flow input is the direct first check. Normal lamp power, UV transmittance, and channel level make the lamp circuit and level transmitter weaker explanations; the sleeve cleaner does not supply the pacing signal.
Two parallel contact basins receive flow from a common inlet. The east basin has 0.4 mg/L chlorine residual at its outlet, while the west basin has 1.1 mg/L chlorine residual at its outlet. What should the operator compare first?
Answer: C. Actual basin flow rates
Comparing actual basin flow rates checks whether unequal hydraulic loading is producing different contact times and outlet residuals. The inlet split-weir settings, outlet sampling locations, and internal baffle condition are plausible nearby checks, but measured basin flow is the most direct first comparison between the parallel units.
A UV channel's validated dose falls below its operating target. Lamp output, UV transmittance, and channel flow are normal, but water depth is 6 in below the channel target. What should the operator check first?
Answer: A. Level-control gate
The 6 in low water depth can reduce the validated UV dose even when lamp output, transmittance, and flow are normal, so the level-control gate is the direct first check. The normal lamp reading makes ballast output a weaker cause, and neither the sleeve wiper nor flowmeter explains the verified low depth.
Why is treated wastewater disinfected before it leaves the plant?
Answer: D. To reduce disease-causing microorganisms before the effluent leaves the plant
Disinfection reduces microorganisms that can cause disease; it does not make wastewater sterile. For example, chlorine or ultraviolet light can lower the number of harmful organisms before discharge. A claims complete removal, B describes nutrient treatment, and C describes settling rather than disinfection.
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