CA Wastewater Grade 3 Sample
Questions and Answers | Latest
Version | 2025/2026 | Correct & Verified
What is the primary purpose of secondary treatment in wastewater plants?
✔✔To biologically remove dissolved and suspended organic matter.
Why is maintaining proper dissolved oxygen levels in an aeration tank important?
✔✔To support microbial activity and prevent anaerobic conditions.
What does the term "MLSS" stand for in wastewater operations?
✔✔Mixed Liquor Suspended Solids.
Why is it necessary to waste sludge from the activated sludge process?
✔✔To maintain a stable biomass and prevent overgrowth of microorganisms.
What is the main difference between primary and secondary clarifiers?
✔✔Primary clarifiers settle solids, while secondary clarifiers separate biological floc.
1
,What is the purpose of a return activated sludge (RAS) line?
✔✔To recycle settled biomass back into the aeration tank.
Why is filamentous bacteria problematic in secondary treatment?
✔✔It causes poor settling and sludge bulking.
What laboratory test measures the oxygen consumed by microorganisms in five days?
✔✔Biochemical Oxygen Demand (BOD5).
Why is nitrification important in wastewater treatment?
✔✔It converts ammonia into nitrite and then nitrate.
What is the main function of denitrification in wastewater plants?
✔✔To reduce nitrate to nitrogen gas, removing nitrogen from the water.
Why is maintaining pH within a neutral range important in biological treatment?
✔✔Microorganisms function best in a balanced pH range.
2
,What is the purpose of a digester in sludge treatment?
✔✔To stabilize sludge by breaking down organic matter.
What is one advantage of anaerobic digestion of sludge?
✔✔It produces methane gas that can be used for energy.
Why is polymer often added before sludge dewatering?
✔✔To improve solids separation by coagulating particles.
What is the typical range of solids concentration in primary sludge?
✔✔About 4% to 6%.
Why is chlorination used in wastewater treatment?
✔✔To disinfect and kill pathogenic organisms.
What chemical can be used to remove phosphorus from wastewater?
✔✔Alum or ferric chloride.
3
, What is the main difference between BOD and COD tests?
✔✔BOD measures biological oxygen demand, COD measures total chemical oxygen demand.
Why is it important to monitor temperature in anaerobic digesters?
✔✔Microbial activity depends on maintaining mesophilic or thermophilic conditions.
What does SVI stand for in wastewater testing?
✔✔Sludge Volume Index.
What problem does a high SVI indicate?
✔✔Poor settling sludge or bulking conditions.
What is the purpose of grit removal in preliminary treatment?
✔✔To prevent damage and abrasion to equipment downstream.
Why should influent flow be equalized in treatment plants?
✔✔To prevent hydraulic overload and maintain steady treatment performance.
4
Questions and Answers | Latest
Version | 2025/2026 | Correct & Verified
What is the primary purpose of secondary treatment in wastewater plants?
✔✔To biologically remove dissolved and suspended organic matter.
Why is maintaining proper dissolved oxygen levels in an aeration tank important?
✔✔To support microbial activity and prevent anaerobic conditions.
What does the term "MLSS" stand for in wastewater operations?
✔✔Mixed Liquor Suspended Solids.
Why is it necessary to waste sludge from the activated sludge process?
✔✔To maintain a stable biomass and prevent overgrowth of microorganisms.
What is the main difference between primary and secondary clarifiers?
✔✔Primary clarifiers settle solids, while secondary clarifiers separate biological floc.
1
,What is the purpose of a return activated sludge (RAS) line?
✔✔To recycle settled biomass back into the aeration tank.
Why is filamentous bacteria problematic in secondary treatment?
✔✔It causes poor settling and sludge bulking.
What laboratory test measures the oxygen consumed by microorganisms in five days?
✔✔Biochemical Oxygen Demand (BOD5).
Why is nitrification important in wastewater treatment?
✔✔It converts ammonia into nitrite and then nitrate.
What is the main function of denitrification in wastewater plants?
✔✔To reduce nitrate to nitrogen gas, removing nitrogen from the water.
Why is maintaining pH within a neutral range important in biological treatment?
✔✔Microorganisms function best in a balanced pH range.
2
,What is the purpose of a digester in sludge treatment?
✔✔To stabilize sludge by breaking down organic matter.
What is one advantage of anaerobic digestion of sludge?
✔✔It produces methane gas that can be used for energy.
Why is polymer often added before sludge dewatering?
✔✔To improve solids separation by coagulating particles.
What is the typical range of solids concentration in primary sludge?
✔✔About 4% to 6%.
Why is chlorination used in wastewater treatment?
✔✔To disinfect and kill pathogenic organisms.
What chemical can be used to remove phosphorus from wastewater?
✔✔Alum or ferric chloride.
3
, What is the main difference between BOD and COD tests?
✔✔BOD measures biological oxygen demand, COD measures total chemical oxygen demand.
Why is it important to monitor temperature in anaerobic digesters?
✔✔Microbial activity depends on maintaining mesophilic or thermophilic conditions.
What does SVI stand for in wastewater testing?
✔✔Sludge Volume Index.
What problem does a high SVI indicate?
✔✔Poor settling sludge or bulking conditions.
What is the purpose of grit removal in preliminary treatment?
✔✔To prevent damage and abrasion to equipment downstream.
Why should influent flow be equalized in treatment plants?
✔✔To prevent hydraulic overload and maintain steady treatment performance.
4
