CA Wastewater Grade V Questions
and Answers | Latest Version |
2025/2026 | Correct & Verified
What is the primary purpose of an equalization basin in a treatment plant?
✔✔To balance flow and load variations before treatment.
Why is alkalinity important in nitrification?
✔✔It provides buffering capacity to maintain pH as nitrifiers consume alkalinity.
What is the main difference between mesophilic and thermophilic digestion?
✔✔Mesophilic digestion operates around 30–38°C, while thermophilic digestion operates
around 50–60°C.
Why is maintaining a proper food-to-microorganism (F/M) ratio important in activated sludge?
✔✔It prevents issues such as bulking or low treatment efficiency.
What is the purpose of wasting sludge in the activated sludge process?
✔✔To control the age and concentration of microorganisms.
1
,Why must dissolved oxygen levels be maintained in aeration basins?
✔✔To support aerobic microbial activity for organic matter removal.
What causes rising sludge in secondary clarifiers?
✔✔Denitrification producing nitrogen gas bubbles that float solids.
Why is chlorine demand higher in wastewater than in drinking water?
✔✔Because wastewater contains more organic and inorganic compounds that consume chlorine.
What is the purpose of secondary clarifiers in activated sludge systems?
✔✔To settle biological solids and return or waste them.
Why is pH control important during chemical phosphorus removal?
✔✔Because chemical precipitation reactions are pH-dependent.
What is the main advantage of using ultraviolet disinfection instead of chlorine?
✔✔It kills pathogens without producing harmful disinfection by-products.
2
,What type of bacteria perform nitrification?
✔✔Autotrophic aerobic bacteria such as Nitrosomonas and Nitrobacter.
What is the end product of denitrification?
✔✔Nitrogen gas released to the atmosphere.
Why is sludge thickening performed before dewatering?
✔✔To reduce water content and improve dewatering efficiency.
What is the purpose of a digester gas flare system?
✔✔To safely burn excess methane gas.
Why must hydrogen sulfide be controlled in wastewater systems?
✔✔It causes odor, corrosion, and safety hazards.
What is the purpose of using coagulants in wastewater treatment?
✔✔To destabilize and remove colloidal particles.
3
, What is the relationship between SVI and sludge settleability?
✔✔A low SVI indicates good settling, while a high SVI indicates bulking.
Why is dissolved oxygen monitoring critical in final effluent?
✔✔Because low DO can harm aquatic life in receiving waters.
What is the purpose of return activated sludge (RAS)?
✔✔To maintain the microbial population in the aeration basin.
Why is wasting sludge to a digester beneficial?
✔✔It stabilizes organic matter and reduces pathogens.
What operational issue does filamentous bacteria overgrowth cause?
✔✔Sludge bulking and poor settling in secondary clarifiers.
What is the main purpose of tertiary filtration?
✔✔To remove fine suspended solids before disinfection.
4
and Answers | Latest Version |
2025/2026 | Correct & Verified
What is the primary purpose of an equalization basin in a treatment plant?
✔✔To balance flow and load variations before treatment.
Why is alkalinity important in nitrification?
✔✔It provides buffering capacity to maintain pH as nitrifiers consume alkalinity.
What is the main difference between mesophilic and thermophilic digestion?
✔✔Mesophilic digestion operates around 30–38°C, while thermophilic digestion operates
around 50–60°C.
Why is maintaining a proper food-to-microorganism (F/M) ratio important in activated sludge?
✔✔It prevents issues such as bulking or low treatment efficiency.
What is the purpose of wasting sludge in the activated sludge process?
✔✔To control the age and concentration of microorganisms.
1
,Why must dissolved oxygen levels be maintained in aeration basins?
✔✔To support aerobic microbial activity for organic matter removal.
What causes rising sludge in secondary clarifiers?
✔✔Denitrification producing nitrogen gas bubbles that float solids.
Why is chlorine demand higher in wastewater than in drinking water?
✔✔Because wastewater contains more organic and inorganic compounds that consume chlorine.
What is the purpose of secondary clarifiers in activated sludge systems?
✔✔To settle biological solids and return or waste them.
Why is pH control important during chemical phosphorus removal?
✔✔Because chemical precipitation reactions are pH-dependent.
What is the main advantage of using ultraviolet disinfection instead of chlorine?
✔✔It kills pathogens without producing harmful disinfection by-products.
2
,What type of bacteria perform nitrification?
✔✔Autotrophic aerobic bacteria such as Nitrosomonas and Nitrobacter.
What is the end product of denitrification?
✔✔Nitrogen gas released to the atmosphere.
Why is sludge thickening performed before dewatering?
✔✔To reduce water content and improve dewatering efficiency.
What is the purpose of a digester gas flare system?
✔✔To safely burn excess methane gas.
Why must hydrogen sulfide be controlled in wastewater systems?
✔✔It causes odor, corrosion, and safety hazards.
What is the purpose of using coagulants in wastewater treatment?
✔✔To destabilize and remove colloidal particles.
3
, What is the relationship between SVI and sludge settleability?
✔✔A low SVI indicates good settling, while a high SVI indicates bulking.
Why is dissolved oxygen monitoring critical in final effluent?
✔✔Because low DO can harm aquatic life in receiving waters.
What is the purpose of return activated sludge (RAS)?
✔✔To maintain the microbial population in the aeration basin.
Why is wasting sludge to a digester beneficial?
✔✔It stabilizes organic matter and reduces pathogens.
What operational issue does filamentous bacteria overgrowth cause?
✔✔Sludge bulking and poor settling in secondary clarifiers.
What is the main purpose of tertiary filtration?
✔✔To remove fine suspended solids before disinfection.
4
