ABC WASTEWATER TREATMENT OPERATOR CLASS
II EXAM NEWEST 2025- 2026 UPDATE 100
QUESTIONS & 100% CORRECT ANSWERS GRADED
A+ (BRAND NEW!!)
Content Focus: Activated Sludge Process Control, Disinfection,
Solids Handling, Laboratory Analysis, Safety, Pumps & Hydraulics,
Regulations, Troubleshooting (Most Tested Areas)
1. What is the primary purpose of the aeration tank in the activated sludge
process?
To provide oxygen for microorganisms to biologically degrade
organic matter
Microorganisms require dissolved oxygen to metabolize organic
pollutants, reducing BOD.
2. What parameter indicates the amount of oxygen available to
microorganisms in aeration?
Dissolved oxygen (DO)
DO directly measures oxygen concentration essential for aerobic
treatment.
3. What is the typical DO range maintained in an aeration basin?
1.0–3.0 mg/L
This range supports microbial activity without wasting energy
from over-aeration.
4. What does BOD measure in wastewater?
The amount of biodegradable organic matter
BOD reflects oxygen required by microbes to decompose organic
pollutants.
, 5. What is the main function of the secondary clarifier?
To separate biological solids from treated water
Settling allows biomass to be removed or recycled.
6. What is return activated sludge (RAS)?
Settled sludge returned to the aeration tank
RAS maintains sufficient microbial population for treatment.
7. What is waste activated sludge (WAS)?
Excess sludge removed from the system
WAS controls biomass concentration and sludge age.
8. What does MLSS stand for?
Mixed Liquor Suspended Solids
Represents total suspended solids in the aeration tank.
9. What does MLVSS represent?
The organic (volatile) portion of MLSS
This fraction approximates living biomass.
10.What is sludge age (SRT)?
Average time microorganisms remain in the system
Controls biological stability and treatment efficiency.
11.What problem occurs if sludge age is too low?
Washout of microorganisms
Insufficient biomass reduces treatment performance.
12.What is bulking sludge characterized by?
Poor settling and high sludge blanket levels
Often caused by filamentous bacteria overgrowth.
13.What test measures settleability of activated sludge?
Sludge Volume Index (SVI)
SVI relates settled sludge volume to MLSS concentration.
II EXAM NEWEST 2025- 2026 UPDATE 100
QUESTIONS & 100% CORRECT ANSWERS GRADED
A+ (BRAND NEW!!)
Content Focus: Activated Sludge Process Control, Disinfection,
Solids Handling, Laboratory Analysis, Safety, Pumps & Hydraulics,
Regulations, Troubleshooting (Most Tested Areas)
1. What is the primary purpose of the aeration tank in the activated sludge
process?
To provide oxygen for microorganisms to biologically degrade
organic matter
Microorganisms require dissolved oxygen to metabolize organic
pollutants, reducing BOD.
2. What parameter indicates the amount of oxygen available to
microorganisms in aeration?
Dissolved oxygen (DO)
DO directly measures oxygen concentration essential for aerobic
treatment.
3. What is the typical DO range maintained in an aeration basin?
1.0–3.0 mg/L
This range supports microbial activity without wasting energy
from over-aeration.
4. What does BOD measure in wastewater?
The amount of biodegradable organic matter
BOD reflects oxygen required by microbes to decompose organic
pollutants.
, 5. What is the main function of the secondary clarifier?
To separate biological solids from treated water
Settling allows biomass to be removed or recycled.
6. What is return activated sludge (RAS)?
Settled sludge returned to the aeration tank
RAS maintains sufficient microbial population for treatment.
7. What is waste activated sludge (WAS)?
Excess sludge removed from the system
WAS controls biomass concentration and sludge age.
8. What does MLSS stand for?
Mixed Liquor Suspended Solids
Represents total suspended solids in the aeration tank.
9. What does MLVSS represent?
The organic (volatile) portion of MLSS
This fraction approximates living biomass.
10.What is sludge age (SRT)?
Average time microorganisms remain in the system
Controls biological stability and treatment efficiency.
11.What problem occurs if sludge age is too low?
Washout of microorganisms
Insufficient biomass reduces treatment performance.
12.What is bulking sludge characterized by?
Poor settling and high sludge blanket levels
Often caused by filamentous bacteria overgrowth.
13.What test measures settleability of activated sludge?
Sludge Volume Index (SVI)
SVI relates settled sludge volume to MLSS concentration.
