Washington Wastewater Treatment Plant Operator Group IV Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

Washington Wastewater Treatment Plant Operator Group IV Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of disinfection in a wastewater treatment

plant?

• Remove total suspended solids
• Destroy or inactivate pathogenic organisms
• Remove nutrients (nitrogen and phosphorus)
• Increase sludge settling rate

* Rationale: Disinfection targets pathogens to protect public health; it

is not primarily for solids removal or nutrient removal.*

• Which of the following disinfection methods produces no residual

disinfectant?

• Chlorination 1 / 4

• Ultraviolet (UV)
• Ozonation
• Chloramine

* Rationale: UV disinfection uses light, leaving no chemical residual in

the effluent.*

• During anaerobic digestion, what gas is primarily produced?
• Oxygen
• Nitrogen
• Methane
• Carbon monoxide

* Rationale: Methane is the major biogas produced during anaerobic

digestion.*

• Which safety procedure is most critical before entering a confined

space in a wastewater plant?

• Checking pH
• Running pumps
• Lockout/tagout and atmospheric testing
• Turning on a blower

* Rationale: Lockout/tagout ensures equipment is de-energized, and

atmospheric testing checks for toxic or oxygen-deficient air.*

• In process control, what is the importance of dissolved oxygen (DO)

measurement in an activated sludge plant?

• To monitor pH 2 / 4

• To calculate sludge volume index
• To ensure aerobic conditions for bacteria
• To measure turbidity

* Rationale: Aerobic bacteria require dissolved oxygen; maintaining

DO is critical for process performance.*

6. The sludge volume index (SVI) is used to:

• Measure nutrient concentration
• Assess the settling characteristics of activated sludge
• Calculate digester gas generation
• Determine disinfection dose

* Rationale: SVI indicates how well sludge settles; a key parameter in

evaluating sludge settleability.*

• Which analyte would you sample for to estimate the organic strength

of influent wastewater?

• Nitrates
• Biochemical oxygen demand (BOD)
• pH
• Total dissolved solids

* Rationale: BOD measures the oxygen demand exerted by

biodegradable organic matter—a common measure of organic strength.*

• What is the effect of increasing the recycle (return activated sludge)

rate too high in an activated sludge system? 3 / 4

• Poor settling (bulking)
• Excess sludge production
• High effluent BOD
• Increased disinfection requirement

* Rationale: Too much recycle may lead to overloaded solids and poor

sludge settling (bulking).*

• For controlling filamentous bacteria, which operational adjustment is

typically made?

• Lower the pH to 4
• Increase the dissolved oxygen concentration
• Reduce sludge wasting
• Stop aeration

* Rationale: Higher DO helps favor floc-forming bacteria over

filamentous species, improving sludge structure.*

• What is the primary role of a clarifier in a conventional activated

sludge plant?

• Aerate the mixed liquor
• Disinfect the effluent
• Separate solids from treated water
• Digest sludge

* Rationale: Clarifiers allow solids to settle so that treated effluent can

be separated from biomass.*

• / 4