ABC WASTEWATER LEVEL 3 CERTIFICATION | COMPLETE EXAM
2026/2027 | QUESTIONS AND 100% VERIFIED ANSWERS | PASS
GUARANTEE
ABC Wastewater Level 3 Certification
Q: What is the typical Food-to-Microorganism (F/M) ratio for a
conventional activated sludge plant? ANSWER 0.2 to 0.5 lbs BOD/lb
MLVSS/day.
Q: What does SVI stand for? ANSWER Sludge Volume Index.
Q: What is the target SVI range for a well-settling sludge? ANSWER 80
to 150 mL/g.
Q: What does an SVI greater than 200 indicate? ANSWER Bulking
sludge.
Q: What is the formula for Mean Cell Residence Time (MCRT)? ANSWER
(MLSS lbs in aeration + MLSS lbs in clarifier) / (WAS lbs/day + Effluent
SS lbs/day).
Q: A high MCRT typically results in what biological condition? ANSWER
Nitrification.
Q: What type of bacteria are responsible for nitrification? ANSWER
Nitrosomonas and Nitrobacter.
Q: What is the biological process of converting ammonia to nitrate
called? ANSWER Nitrification.
Q: What is the process of converting nitrate to nitrogen gas called?
ANSWER Denitrification.
Q: Denitrification requires an anoxic environment. What else does it
require? ANSWER A carbon source (BOD).
,Q: What visual clue indicates denitrification is occurring in a secondary
clarifier? ANSWER Rising sludge (nitrogen gas bubbles lifting the
sludge).
Q: How do you correct rising sludge in a clarifier? ANSWER Increase
return sludge rate or increase WAS rate to reduce detention time.
Q: What is "old sludge"? ANSWER Sludge with a low F/M ratio and high
MCRT.
Q: What is a common visual symptom of old sludge? ANSWER Pin floc
and turbid effluent.
Q: What is "young sludge"? ANSWER Sludge with a high F/M ratio and
low MCRT.
Q: What is a common symptom of young sludge? ANSWER Ashy gray
foam and high effluent BOD.
Q: What causes filamentous bulking? ANSWER Low F/M, low DO, or
nutrient deficiency.
Q: Name two common filaments associated with low DO bulking.
ANSWER Sphaerotilus natans and Type 1701.
Q: Name a common filament associated with low F/M (septicity) bulking.
ANSWER Microthrix parvicella.
Q: What is the most common method to control filamentous bulking?
ANSWER Chlorination of the return activated sludge (RAS).
Q: Where should chlorine be applied to target filaments without killing
floc-formers? ANSWER To the RAS line.
Q: What is the target chlorine dose for RAS chlorination? ANSWER 2 to
4 lbs Cl2/1000 lbs MLVSS/day.
Q: What is the ideal dissolved oxygen (DO) level in the aeration basin?
ANSWER 1.0 to 3.0 mg/L.
Q: What happens if DO drops below 0.5 mg/L in the aeration basin?
ANSWER Filamentous growth, septicity, and incomplete BOD removal.
Q: What is the purpose of the RAS? ANSWER To return settled
microorganisms from the clarifier back to the aeration basin to
maintain the MLSS concentration.
, Q: What is the purpose of Waste Activated Sludge (WAS)? ANSWER To
remove excess microorganisms to control the MCRT/F/M ratio.
Q: What is MLSS? ANSWER Mixed Liquor Suspended Solids.
Q: What is MLVSS? ANSWER Mixed Liquor Volatile Suspended Solids
(the living portion of the solids).
Q: Typically, what percentage of MLSS is MLVSS? ANSWER 60% to 80%.
Q: What is a diffused aeration system? ANSWER A system that pumps
air through submerged diffusers to transfer oxygen into the
wastewater.
Q: What is fine bubble diffusion compared to coarse bubble? ANSWER
Fine bubble has higher oxygen transfer efficiency (OTE) but is more
prone to clogging.
Q: What is alpha (
α
) in aeration calculations? ANSWER The ratio of wastewater OTE to
clean water OTE (usually 0.3 to 0.5).
Q: What is beta (
β
) in aeration calculations? ANSWER The ratio of oxygen solubility in
wastewater to clean water (usually 0.9 to 0.98).
Q: What is the purpose of anoxic zones in an A2O process? ANSWER
To promote denitrification and phosphorus release.
Q: What is the purpose of anaerobic zones in biological phosphorus
removal? ANSWER To force phosphorus accumulating organisms
(PAOs) to release phosphorus.
Q: Where does phosphorus uptake occur in a BPR plant? ANSWER In
the aerobic zone.
Q: What is a selector? ANSWER A small tank at the head of the
aeration basin designed to favor floc-formers over filaments.
Q: What are the three types of selectors? ANSWER Anaerobic, anoxic,
and aerobic.
2026/2027 | QUESTIONS AND 100% VERIFIED ANSWERS | PASS
GUARANTEE
ABC Wastewater Level 3 Certification
Q: What is the typical Food-to-Microorganism (F/M) ratio for a
conventional activated sludge plant? ANSWER 0.2 to 0.5 lbs BOD/lb
MLVSS/day.
Q: What does SVI stand for? ANSWER Sludge Volume Index.
Q: What is the target SVI range for a well-settling sludge? ANSWER 80
to 150 mL/g.
Q: What does an SVI greater than 200 indicate? ANSWER Bulking
sludge.
Q: What is the formula for Mean Cell Residence Time (MCRT)? ANSWER
(MLSS lbs in aeration + MLSS lbs in clarifier) / (WAS lbs/day + Effluent
SS lbs/day).
Q: A high MCRT typically results in what biological condition? ANSWER
Nitrification.
Q: What type of bacteria are responsible for nitrification? ANSWER
Nitrosomonas and Nitrobacter.
Q: What is the biological process of converting ammonia to nitrate
called? ANSWER Nitrification.
Q: What is the process of converting nitrate to nitrogen gas called?
ANSWER Denitrification.
Q: Denitrification requires an anoxic environment. What else does it
require? ANSWER A carbon source (BOD).
,Q: What visual clue indicates denitrification is occurring in a secondary
clarifier? ANSWER Rising sludge (nitrogen gas bubbles lifting the
sludge).
Q: How do you correct rising sludge in a clarifier? ANSWER Increase
return sludge rate or increase WAS rate to reduce detention time.
Q: What is "old sludge"? ANSWER Sludge with a low F/M ratio and high
MCRT.
Q: What is a common visual symptom of old sludge? ANSWER Pin floc
and turbid effluent.
Q: What is "young sludge"? ANSWER Sludge with a high F/M ratio and
low MCRT.
Q: What is a common symptom of young sludge? ANSWER Ashy gray
foam and high effluent BOD.
Q: What causes filamentous bulking? ANSWER Low F/M, low DO, or
nutrient deficiency.
Q: Name two common filaments associated with low DO bulking.
ANSWER Sphaerotilus natans and Type 1701.
Q: Name a common filament associated with low F/M (septicity) bulking.
ANSWER Microthrix parvicella.
Q: What is the most common method to control filamentous bulking?
ANSWER Chlorination of the return activated sludge (RAS).
Q: Where should chlorine be applied to target filaments without killing
floc-formers? ANSWER To the RAS line.
Q: What is the target chlorine dose for RAS chlorination? ANSWER 2 to
4 lbs Cl2/1000 lbs MLVSS/day.
Q: What is the ideal dissolved oxygen (DO) level in the aeration basin?
ANSWER 1.0 to 3.0 mg/L.
Q: What happens if DO drops below 0.5 mg/L in the aeration basin?
ANSWER Filamentous growth, septicity, and incomplete BOD removal.
Q: What is the purpose of the RAS? ANSWER To return settled
microorganisms from the clarifier back to the aeration basin to
maintain the MLSS concentration.
, Q: What is the purpose of Waste Activated Sludge (WAS)? ANSWER To
remove excess microorganisms to control the MCRT/F/M ratio.
Q: What is MLSS? ANSWER Mixed Liquor Suspended Solids.
Q: What is MLVSS? ANSWER Mixed Liquor Volatile Suspended Solids
(the living portion of the solids).
Q: Typically, what percentage of MLSS is MLVSS? ANSWER 60% to 80%.
Q: What is a diffused aeration system? ANSWER A system that pumps
air through submerged diffusers to transfer oxygen into the
wastewater.
Q: What is fine bubble diffusion compared to coarse bubble? ANSWER
Fine bubble has higher oxygen transfer efficiency (OTE) but is more
prone to clogging.
Q: What is alpha (
α
) in aeration calculations? ANSWER The ratio of wastewater OTE to
clean water OTE (usually 0.3 to 0.5).
Q: What is beta (
β
) in aeration calculations? ANSWER The ratio of oxygen solubility in
wastewater to clean water (usually 0.9 to 0.98).
Q: What is the purpose of anoxic zones in an A2O process? ANSWER
To promote denitrification and phosphorus release.
Q: What is the purpose of anaerobic zones in biological phosphorus
removal? ANSWER To force phosphorus accumulating organisms
(PAOs) to release phosphorus.
Q: Where does phosphorus uptake occur in a BPR plant? ANSWER In
the aerobic zone.
Q: What is a selector? ANSWER A small tank at the head of the
aeration basin designed to favor floc-formers over filaments.
Q: What are the three types of selectors? ANSWER Anaerobic, anoxic,
and aerobic.
