Operator Certification Practice Exam

Biological Industrial Waste Treatment Operator Certification Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the main purpose of biological waste treatment?
• To remove heavy metals
• To degrade organic matter using microorganisms
• To separate solids mechanically
• To neutralize acids

Rationale: Biological treatment relies on microbial metabolism to convert

organic pollutants into stable end products such as CO₂, water, and biomass._

• In activated sludge, what does "MLSS" stand for?
• Mixed Liquor Solids and Sludge 1 / 4

• Mixed Liquor Suspended Solids
• Microbial Load of Settled Sludge
• Mean Liquid Solid Suspension

Rationale: MLSS represents the concentration of suspended solids, mostly

microorganisms, in the aeration tank, used to monitor biomass levels._

• Which process primarily removes biochemical oxygen demand (BOD)?
• Screening
• Biological oxidation
• Sedimentation
• Filtration

Rationale: BOD is reduced through microbial oxidation of organic material

in biological processes._

4. The main function of an aeration tank is to:

• Separate sludge
• Supply oxygen and mix microorganisms with wastewater
• Clarify water
• Measure pH

Rationale: Aeration maintains dissolved oxygen and keeps biomass

suspended for effective treatment._

• / 4

• What does F/M ratio represent?
• Food to microorganism ratio
• Flow to mass ratio
• Feed to mixture ratio
• Final microbial ratio

Rationale: The F/M ratio indicates the balance between organic load and

microbial population, critical for process stability._

• What is the typical range for dissolved oxygen (DO) in an aeration tank?
• 0–0.5 mg/L
• 0.5–1.0 mg/L
• 1.5–3.0 mg/L
• 5–10 mg/L

Rationale: A DO range of 1.5–3.0 mg/L supports aerobic microbial activity

without energy waste._

• What causes sludge bulking?
• Low BOD
• Excess filamentous bacteria growth
• High oxygen levels
• Low temperature

Rationale: Filamentous bacteria prevent proper sludge settling, leading to

bulking._ 3 / 4

• Which microorganism type dominates in aerobic treatment?
• Anaerobes
• Aerobes
• Facultative bacteria
• Methanogens

Rationale: Aerobic systems depend on oxygen-loving microorganisms for

organic degradation._

• What is the purpose of secondary clarification?
• Oxidize ammonia
• Add chemicals
• Separate biological solids from treated effluent
• Filter water

Rationale: The secondary clarifier settles biomass after aeration for return

or wasting._

• What does “SRT” mean in wastewater treatment?
• Sludge Reactivity Time
• System Retention Time
• Solids Retention Time
• Settled Residual Total
• / 4