ABC Wastewater Level 3 Certification:
Study Guide & Practice Exam Questions
with Correct Answers Updated 2025
100% Guaranteed Pass!!!A+
Graded<<Brand New Version>>
Exam Focus: The Level 3 exam (often for Chief Plant Operator or Superintendent)
focuses on advanced technical knowledge, complex problem-solving, managerial duties,
and regulatory compliance. You are expected to not just know what to do, but why it's
done and how to manage the entire process.
Section 1: Preliminary & Primary Treatment
1. What is the primary purpose of preliminary treatment?
ANSWER ✓ To remove materials that could damage equipment, clog pipes, or hinder
subsequent treatment processes, such as rags, sticks, grit, and large solids.
2. Name three common types of screens and their typical application.
ANSWER ✓ 1) Bar Screens (Coarse): Remove large debris. 2) Fine Screens: Remove
smaller particles, often before advanced treatment. 3) Step or Drum Screens
(Mechanical): Automated screens for larger plants.
3. A grit chamber is designed to remove settleable inorganic solids based on what
principle?
ANSWER ✓ Gravity sedimentation, with controlled velocity (typically ~1 ft/sec) to allow
heavier grit to settle while keeping lighter organic solids in suspension.
4. What operational problem occurs if grit removal is ineffective?
ANSWER ✓ Grit accumulation in clarifiers, digesters, and aeration basins, leading to
excessive wear on pumps and equipment, reduced tank volume, and costly removal.
, 5. What is the key indicator of a well-operating primary clarifier?
ANSWER ✓ Consistent removal of 50-65% of Total Suspended Solids (TSS) and 25-40%
of Biochemical Oxygen Demand (BOD).
6. Describe two methods for controlling scum in a primary clarifier.
ANSWER ✓ 1) Skimming Mechanisms: Automatic skimmers that collect scum into a
scum trough. 2) Baffles: Submerged scum baffles to prevent wind from blowing scum
over the weirs.
7. A sudden drop in primary clarifier efficiency could be caused by what?
ANSWER ✓ Hydraulic overload, septic wastewater (causing solids to float), toxic influent
killing microbes, or a malfunctioning sludge collection mechanism.
Section 2: Biological Treatment (Activated Sludge)
8. The activated sludge process is fundamentally a ______ process.
ANSWER ✓ Biological (aerobic), where microorganisms metabolize organic matter in the
wastewater.
9. Define Food-to-Microorganism (F/M) ratio.
ANSWER ✓ It is a process control calculation that represents the amount of food (BOD
or COD) entering the aeration basin relative to the mass of microorganisms (MLVSS)
present.
10. Calculate the F/M ratio given: Flow = 2.0 MGD, Primary Effluent BOD = 150
mg/L, Aeration Tank Volume = 0.50 MG, MLVSS = 2,500 mg/L.
ANSWER ✓
F = (Flow) x (BOD) x 8.34 = (2.0) x (150) x (8.34) = 2,502 lbs/day BOD
M = (Tank Vol) x (MLVSS) x 8.34 = (0.50) x (2500) x (8.34) = 10,425 lbs MLVSS
F/M = 2,,425 = 0.24 lb BOD/lb MLVSS/day
11. What does a high F/M ratio indicate?
ANSWER ✓ There is more food available than the microorganisms can consume, leading
to poor treatment, turbid effluent, and possible bulking.
12. What does a low F/M ratio indicate?
ANSWER ✓ The microorganisms are starved, leading to endogenous respiration,
pinpoint floc, and a clear but possibly high in ammonia effluent (if nitrifying).
Study Guide & Practice Exam Questions
with Correct Answers Updated 2025
100% Guaranteed Pass!!!A+
Graded<<Brand New Version>>
Exam Focus: The Level 3 exam (often for Chief Plant Operator or Superintendent)
focuses on advanced technical knowledge, complex problem-solving, managerial duties,
and regulatory compliance. You are expected to not just know what to do, but why it's
done and how to manage the entire process.
Section 1: Preliminary & Primary Treatment
1. What is the primary purpose of preliminary treatment?
ANSWER ✓ To remove materials that could damage equipment, clog pipes, or hinder
subsequent treatment processes, such as rags, sticks, grit, and large solids.
2. Name three common types of screens and their typical application.
ANSWER ✓ 1) Bar Screens (Coarse): Remove large debris. 2) Fine Screens: Remove
smaller particles, often before advanced treatment. 3) Step or Drum Screens
(Mechanical): Automated screens for larger plants.
3. A grit chamber is designed to remove settleable inorganic solids based on what
principle?
ANSWER ✓ Gravity sedimentation, with controlled velocity (typically ~1 ft/sec) to allow
heavier grit to settle while keeping lighter organic solids in suspension.
4. What operational problem occurs if grit removal is ineffective?
ANSWER ✓ Grit accumulation in clarifiers, digesters, and aeration basins, leading to
excessive wear on pumps and equipment, reduced tank volume, and costly removal.
, 5. What is the key indicator of a well-operating primary clarifier?
ANSWER ✓ Consistent removal of 50-65% of Total Suspended Solids (TSS) and 25-40%
of Biochemical Oxygen Demand (BOD).
6. Describe two methods for controlling scum in a primary clarifier.
ANSWER ✓ 1) Skimming Mechanisms: Automatic skimmers that collect scum into a
scum trough. 2) Baffles: Submerged scum baffles to prevent wind from blowing scum
over the weirs.
7. A sudden drop in primary clarifier efficiency could be caused by what?
ANSWER ✓ Hydraulic overload, septic wastewater (causing solids to float), toxic influent
killing microbes, or a malfunctioning sludge collection mechanism.
Section 2: Biological Treatment (Activated Sludge)
8. The activated sludge process is fundamentally a ______ process.
ANSWER ✓ Biological (aerobic), where microorganisms metabolize organic matter in the
wastewater.
9. Define Food-to-Microorganism (F/M) ratio.
ANSWER ✓ It is a process control calculation that represents the amount of food (BOD
or COD) entering the aeration basin relative to the mass of microorganisms (MLVSS)
present.
10. Calculate the F/M ratio given: Flow = 2.0 MGD, Primary Effluent BOD = 150
mg/L, Aeration Tank Volume = 0.50 MG, MLVSS = 2,500 mg/L.
ANSWER ✓
F = (Flow) x (BOD) x 8.34 = (2.0) x (150) x (8.34) = 2,502 lbs/day BOD
M = (Tank Vol) x (MLVSS) x 8.34 = (0.50) x (2500) x (8.34) = 10,425 lbs MLVSS
F/M = 2,,425 = 0.24 lb BOD/lb MLVSS/day
11. What does a high F/M ratio indicate?
ANSWER ✓ There is more food available than the microorganisms can consume, leading
to poor treatment, turbid effluent, and possible bulking.
12. What does a low F/M ratio indicate?
ANSWER ✓ The microorganisms are starved, leading to endogenous respiration,
pinpoint floc, and a clear but possibly high in ammonia effluent (if nitrifying).
