South Dakota Wastewater Treatment Operator Class III Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf
- Which process is primarily used for the biological removal of organic
- Coagulation
- Sedimentation
- Activated Sludge
- Filtration
matter from wastewater?
Rationale: Activated sludge uses microorganisms to biologically
oxidize organic matter, which is the main method for BOD removal.
- What is the typical range for mixed liquor suspended solids (MLSS) in
an activated sludge process? 1 / 4
- 50–100 mg/L
- 2,000–4,000 mg/L
- 10,000–12,000 mg/L
- 20,000–30,000 mg/L
Rationale: MLSS typically ranges from 2,000 to 4,000 mg/L in
conventional activated sludge systems to maintain sufficient microbial population.
- The term “sludge age” or “mean cell residence time (MCRT)” refers to:
- The hydraulic retention time of the plant
- The average time microorganisms remain in the system
- The settling time of sludge in the clarifier
- The time sludge is held in the digesters
Rationale: Sludge age indicates the average time biomass stays in
the system, important for biological process stability.
4. Nitrification in wastewater treatment converts:
- Nitrogen gas to ammonia
- Ammonia to nitrogen gas
- Ammonia to nitrate
- Nitrate to ammonia
Rationale: Nitrification is a two-step biological process where
ammonia is first oxidized to nitrite and then to nitrate.
5. Denitrification is a biological process that converts nitrate to:
- Ammonia 2 / 4
- Nitrite
- Nitrogen dioxide
- Nitrogen gas
Rationale: Denitrifying bacteria convert nitrate to nitrogen gas,
which is released to the atmosphere, removing nitrogen from wastewater.
6. The primary purpose of a grit chamber is to:
- Remove organic matter
- Remove heavy inorganic solids
- Remove pathogens
- Remove fats, oils, and grease
Rationale: Grit chambers remove sand, gravel, and other heavy
inorganic solids to protect downstream equipment.
7. BOD5 is a measure of:
- Total suspended solids
- Chemical oxygen demand
- Biochemical oxygen demand over 5 days
- Nitrate concentration
Rationale: BOD5 measures the amount of oxygen microorganisms
consume over 5 days while decomposing organic matter.
- What is the primary goal of primary treatment?
- Remove nutrients
- Disinfect wastewater 3 / 4
- Remove settleable solids
- Remove dissolved organics
Rationale: Primary treatment mainly removes settleable solids and
floating material through sedimentation.
- Which of the following is a common method for sludge thickening?
- Trickling filter
- Gravity thickening
- Aeration
- Chlorination
Rationale: Gravity thickening concentrates sludge by allowing water
to rise while solids settle.
- What does F/M ratio in activated sludge systems represent?
- Flow per meter
- Food to microorganism ratio
- Filtration rate
- Free ammonia concentration
Rationale: F/M ratio is the mass of BOD applied per mass of
microorganisms in the aeration tank, affecting system performance.
- The presence of filamentous bacteria in activated sludge may
cause:
- Improved settling
- Bulking sludge
- Increased nitrification
- / 4