Practice Exam Questions And Correct

Indiana Wastewater Operator Class IV Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of preliminary treatment in wastewater

facilities?

• Nutrient removal
• Biological oxygen demand reduction
• Screening and grit removal
• Sludge stabilization

Removes large solids and abrasive materials to protect downstream equipment.

2. The term MLSS in activated sludge refers to:

• Mixed liquor suspended substrate
• Mixed liquor suspended solids 1 / 4

• Mean liquid soluble solids
• Mixed liquor sludge solids

MLSS measures biomass concentration in the aeration basin.

• A clarifier experiences short-circuiting. Which factor is most likely

responsible?

• High sludge age
• Hydraulic overload
• Low weir loading
• Excessive return sludge

Excess flow reduces detention time and reduces settling efficiency.

• What is the typical pH range for optimal nitrification?
• 4.0–5.0
• 5.5–6.0
• 7.0–8.5
• 9.0–10.0

Nitrifying bacteria prefer near-neutral to slightly alkaline conditions.

• In anaerobic digestion, methane typically comprises what percentage of

biogas?

• 10–20%
• 25–35%
• 40–50% 2 / 4

• 60–70%

Methane is the main energy component of digester gas.

• What indicator is used to assess sludge settling quality in secondary

clarifiers?

• SVI
• TUR
• SVI (Sludge Volume Index)
• COD

SVI quantifies settling characteristics of activated sludge.

• What is the main purpose of RAS in activated sludge?
• To increase DO
• To return settled biomass to the aeration basin
• To thicken sludge
• To disinfect the effluent

RAS maintains adequate microorganism concentration for treatment.

8. A composite sample differs from a grab sample because it:

• Uses fewer containers
• Is collected at a single time
• Represents flow or time-proportional conditions
• Represents only peak flow conditions

Composite sampling better reflects varying wastewater characteristics.

• Which parameter indicates organic loading strength? 3 / 4

• TSS
• F/M ratio
• BOD
• Turbidity

BOD expresses the biodegradable organic matter present.

10. Chlorine demand is defined as:

• Chlorine residual + ORP
• Applied chlorine minus residual chlorine
• Remaining chlorine after breakpoint
• The minimum required to kill all organisms

Shows how much chlorine reacts with substances in water.

• What is the major cause of bulking sludge?
• Protozoa dominance
• High DO levels
• Filamentous bacteria overgrowth
• Excess alkalinity

Filaments prevent sludge compaction in clarifiers.

12. A trickling filter relies primarily on:

• Suspended growth
• Attached growth
• Chemical oxidation
• / 4