WASTEWATER GRADE FOUR PRACTICE
EXAM 2026 FULL QUESTIONS AND
DETAILED SOLUTIONS
●● Units on MCRT Answer: S = lb MLSS in system (AB + Secondary
Clarifiers0
E(dot) = lb/d TSS unintentionally removed in effluent
W(dot) = lb/d TSS intentionally removed in WAS
●● Conventional Activated Sludge: MCRT, F:M, Organic Loading,
MLSS mg/L, Aeration Basin HRT (hours), Qras % of Q Answer: MCRT
= 5 - 15 Days
F:M = 0.2 - 0.4 lb BOD/d*lb MLVSS
OL = 20 - 40 lb BOD/d*1000 ft^3
MLSS = 1500 - 3000 mg/L
HRT = 4 - 8 hours
Qras% = 25 to 50% of Q
●● Extended Aeration Activated Sludge: MCRT, F:M, Organic Loading,
MLSS mg/L, Aeration Basin HRT (hours), Qras % of Q Answer: MCRT
= 20 - 30 Days
F:M = 0.05 - 0.15 lb BOD/d*lb MLVSS
OL = 10 - 25 lb BOD/d*1000 ft^3
,MLSS = 3000 - 6000 mg/L
HRT = 18 - 16 hours
Qras% = 75 to 150% of Q
●● Contact-Stabilization Activated Sludge: MCRT, F:M, Organic
Loading, MLSS mg/L, Aeration Basin HRT (hours), Qras % of Q
Answer: MCRT = 5 - 15 Days
F:M = 0.2 - 0.6 lb BOD/d*lb MLVSS
OL = 60 - 75 lb BOD/d*1000 ft^3
MLSS = Contact: 1000 - 3000 mg/L, Stabilisation: 4000 - 10,000
HRT = Contact: 0.5 - 1 hours, Stabilisation: 3 - 6 hours
Qras% = 25 to 100% of Q
●● Step Feed Activated Sludge: MCRT, F:M, Organic Loading, MLSS
mg/L, Aeration Basin HRT (hours), Qras % of Q Answer: MCRT = 5 -
15 Days
F:M = 0.2 - 0.4 lb BOD/d*lb MLVSS
OL = 20 - 40 lb BOD/d*1000 ft^3
MLSS = 2000 - 3500 mg/L
HRT = 3 - 5 hours
Qras% = 25 to 75% of Q
, ●● Complete Mix Activated Sludge: MCRT, F:M, Organic Loading,
MLSS mg/L, Aeration Basin HRT (hours), Qras % of Q Answer: MCRT
= 5 - 15 Days
F:M = 0.2 - 0.6 lb BOD/d*lb MLVSS
OL = 50 - 120 lb BOD/d*1000 ft^3
MLSS = 3000 - 6000 mg/L
HRT = 3 - 5 hours
Qras% = 25 to 100% of Q
●● T/F: When measuring VA in an anaerobic digester, the final step is to
titrate the sample with sulfuric acid. Answer: False: Titrate 0.1 N of
Sodium hydroxide to the phenolphthalein endpoint (pH =8.3)
●● In order for denitrification to occur, what must happen first? (3
items) Answer: Nitrate must be present
Oxygen must be present
Readily available degradable BOD present
●● 3 criteria for valid BOD results Answer: DO consumed in the blank
must be <0.2 mg/L
DO remaining in each sample bottle >1.0 mg/L
DO consumed in each sample bottle >2.0 mg/L
●● Units on the F:M ratio Answer: Lb BOD / d*lb MLVSS
EXAM 2026 FULL QUESTIONS AND
DETAILED SOLUTIONS
●● Units on MCRT Answer: S = lb MLSS in system (AB + Secondary
Clarifiers0
E(dot) = lb/d TSS unintentionally removed in effluent
W(dot) = lb/d TSS intentionally removed in WAS
●● Conventional Activated Sludge: MCRT, F:M, Organic Loading,
MLSS mg/L, Aeration Basin HRT (hours), Qras % of Q Answer: MCRT
= 5 - 15 Days
F:M = 0.2 - 0.4 lb BOD/d*lb MLVSS
OL = 20 - 40 lb BOD/d*1000 ft^3
MLSS = 1500 - 3000 mg/L
HRT = 4 - 8 hours
Qras% = 25 to 50% of Q
●● Extended Aeration Activated Sludge: MCRT, F:M, Organic Loading,
MLSS mg/L, Aeration Basin HRT (hours), Qras % of Q Answer: MCRT
= 20 - 30 Days
F:M = 0.05 - 0.15 lb BOD/d*lb MLVSS
OL = 10 - 25 lb BOD/d*1000 ft^3
,MLSS = 3000 - 6000 mg/L
HRT = 18 - 16 hours
Qras% = 75 to 150% of Q
●● Contact-Stabilization Activated Sludge: MCRT, F:M, Organic
Loading, MLSS mg/L, Aeration Basin HRT (hours), Qras % of Q
Answer: MCRT = 5 - 15 Days
F:M = 0.2 - 0.6 lb BOD/d*lb MLVSS
OL = 60 - 75 lb BOD/d*1000 ft^3
MLSS = Contact: 1000 - 3000 mg/L, Stabilisation: 4000 - 10,000
HRT = Contact: 0.5 - 1 hours, Stabilisation: 3 - 6 hours
Qras% = 25 to 100% of Q
●● Step Feed Activated Sludge: MCRT, F:M, Organic Loading, MLSS
mg/L, Aeration Basin HRT (hours), Qras % of Q Answer: MCRT = 5 -
15 Days
F:M = 0.2 - 0.4 lb BOD/d*lb MLVSS
OL = 20 - 40 lb BOD/d*1000 ft^3
MLSS = 2000 - 3500 mg/L
HRT = 3 - 5 hours
Qras% = 25 to 75% of Q
, ●● Complete Mix Activated Sludge: MCRT, F:M, Organic Loading,
MLSS mg/L, Aeration Basin HRT (hours), Qras % of Q Answer: MCRT
= 5 - 15 Days
F:M = 0.2 - 0.6 lb BOD/d*lb MLVSS
OL = 50 - 120 lb BOD/d*1000 ft^3
MLSS = 3000 - 6000 mg/L
HRT = 3 - 5 hours
Qras% = 25 to 100% of Q
●● T/F: When measuring VA in an anaerobic digester, the final step is to
titrate the sample with sulfuric acid. Answer: False: Titrate 0.1 N of
Sodium hydroxide to the phenolphthalein endpoint (pH =8.3)
●● In order for denitrification to occur, what must happen first? (3
items) Answer: Nitrate must be present
Oxygen must be present
Readily available degradable BOD present
●● 3 criteria for valid BOD results Answer: DO consumed in the blank
must be <0.2 mg/L
DO remaining in each sample bottle >1.0 mg/L
DO consumed in each sample bottle >2.0 mg/L
●● Units on the F:M ratio Answer: Lb BOD / d*lb MLVSS
