, Question 1
A publicly owned treatment works (POTW) produces a biosolids with a
volatile solids reduction (VSR) of 38% by the Van Kleeck method but 42% by
the EPA-approved mass balance method. Under 40 CFR Part 503, which VSR
determination governs compliance for a Class B biosolids land application?
A. The Van Kleeck result (38%) because it is the more conservative
estimate.
B. The mass balance result (42%) because it is the EPA-preferred method
for anaerobic digestion.
C. Either method may be used, but the lower value must be reported for
compliance.
D. Both methods must be reported, and the higher value determines
compliance.
Correct Answer: B - The mass balance result (42%) because it is
the EPA-preferred method for anaerobic digestion.
RATIONALE
40 CFR Part 503 allows either the Van Kleeck or mass balance method
to demonstrate VSR, but the mass balance method is specifically
approved for anaerobic digestion and typically yields a higher, more
accurate VSR. The regulation does not require reporting both or using
the lower value; the permittee may choose the method that
demonstrates compliance. Van Kleeck is not inherently more
conservative for all processes.
Question 2
A gravity belt thickener receives waste activated sludge (WAS) at 0.8% solids
and produces thickened sludge at 5.5% solids. If the polymer dose is 12 lb/dry
ton and the feed flow is 200,000 gallons per day (gpd), what is the approximate
dry solids mass feed rate in dry tons per day?
A. 6.7 dry tons/day
Page 2
, B. 13.4 dry tons/day
C. 1.34 dry tons/day
D. 0.67 dry tons/day
Correct Answer: A - 6.7 dry tons/day
RATIONALE
Dry solids = 200,000 gal × 8.34 lb/gal × 0.008 = 13,344 lb/day.
Convert to dry tons: 13,344 ÷ 2,000 = 6.67 dry tons/day. Option B
incorrectly doubles the mass, C and D misplace decimal points. This
calculation is fundamental for polymer dosing and thickening
performance.
Question 3
Which of the following conditions would most likely cause a Class A biosolids
process using time-temperature requirements to fail compliance, even if the
required temperature and contact time are met?
A. The biosolids feed contains less than 5% solids.
B. The process uses a batch system rather than continuous flow.
C. The biosolids are not uniformly heated throughout the reactor.
D. The process operates at a lower altitude than the validation study.
Correct Answer: C - The biosolids are not uniformly heated
throughout the reactor.
RATIONALE
40 CFR Part 503 Subpart D requires that all biosolids be uniformly
heated to the specified temperature for the required contact time.
Non-uniform heating creates cold spots where pathogens may survive,
invalidating the process. Feed solids concentration, batch vs.
continuous operation, and altitude are not disqualifying if the
time-temperature regime is achieved uniformly.
Page 3
, Question 4
A mesophilic anaerobic digester exhibits a sudden drop in pH from 7.2 to 6.5,
with a corresponding increase in volatile acids from 200 mg/L to 1,800 mg/L
and a decrease in methane production. Which corrective action is most
appropriate?
A. Increase the sludge feed rate to dilute the volatile acids.
B. Add lime to raise the pH to 7.0 and continue feeding.
C. Stop feeding, reduce mixing, and allow the methanogens to recover.
D. Increase the digester temperature to thermophilic range to accelerate
digestion.
Correct Answer: C - Stop feeding, reduce mixing, and allow the
methanogens to recover.
RATIONALE
The symptoms indicate acid accumulation and methanogen inhibition.
The standard remedy is to stop or reduce feeding, minimize mixing to
prevent oxygen intrusion, and allow the methanogen population to
recover. Adding lime may temporarily raise pH but does not address
the volatile acid buildup; increasing feed or temperature would
exacerbate the imbalance.
Question 5
A biosolids land application site is subject to the aggregate cumulative loading
rate for copper under 40 CFR Part 503. If the soil already has 750 lb/acre of
copper from previous applications and the regulatory limit is 1,500 lb/acre,
what is the maximum additional copper that can be applied?
A. 750 lb/acre
B. 1,500 lb/acre
C. 0 lb/acre
D. 2,250 lb/acre
Correct Answer: A - 750 lb/acre
Page 4
A publicly owned treatment works (POTW) produces a biosolids with a
volatile solids reduction (VSR) of 38% by the Van Kleeck method but 42% by
the EPA-approved mass balance method. Under 40 CFR Part 503, which VSR
determination governs compliance for a Class B biosolids land application?
A. The Van Kleeck result (38%) because it is the more conservative
estimate.
B. The mass balance result (42%) because it is the EPA-preferred method
for anaerobic digestion.
C. Either method may be used, but the lower value must be reported for
compliance.
D. Both methods must be reported, and the higher value determines
compliance.
Correct Answer: B - The mass balance result (42%) because it is
the EPA-preferred method for anaerobic digestion.
RATIONALE
40 CFR Part 503 allows either the Van Kleeck or mass balance method
to demonstrate VSR, but the mass balance method is specifically
approved for anaerobic digestion and typically yields a higher, more
accurate VSR. The regulation does not require reporting both or using
the lower value; the permittee may choose the method that
demonstrates compliance. Van Kleeck is not inherently more
conservative for all processes.
Question 2
A gravity belt thickener receives waste activated sludge (WAS) at 0.8% solids
and produces thickened sludge at 5.5% solids. If the polymer dose is 12 lb/dry
ton and the feed flow is 200,000 gallons per day (gpd), what is the approximate
dry solids mass feed rate in dry tons per day?
A. 6.7 dry tons/day
Page 2
, B. 13.4 dry tons/day
C. 1.34 dry tons/day
D. 0.67 dry tons/day
Correct Answer: A - 6.7 dry tons/day
RATIONALE
Dry solids = 200,000 gal × 8.34 lb/gal × 0.008 = 13,344 lb/day.
Convert to dry tons: 13,344 ÷ 2,000 = 6.67 dry tons/day. Option B
incorrectly doubles the mass, C and D misplace decimal points. This
calculation is fundamental for polymer dosing and thickening
performance.
Question 3
Which of the following conditions would most likely cause a Class A biosolids
process using time-temperature requirements to fail compliance, even if the
required temperature and contact time are met?
A. The biosolids feed contains less than 5% solids.
B. The process uses a batch system rather than continuous flow.
C. The biosolids are not uniformly heated throughout the reactor.
D. The process operates at a lower altitude than the validation study.
Correct Answer: C - The biosolids are not uniformly heated
throughout the reactor.
RATIONALE
40 CFR Part 503 Subpart D requires that all biosolids be uniformly
heated to the specified temperature for the required contact time.
Non-uniform heating creates cold spots where pathogens may survive,
invalidating the process. Feed solids concentration, batch vs.
continuous operation, and altitude are not disqualifying if the
time-temperature regime is achieved uniformly.
Page 3
, Question 4
A mesophilic anaerobic digester exhibits a sudden drop in pH from 7.2 to 6.5,
with a corresponding increase in volatile acids from 200 mg/L to 1,800 mg/L
and a decrease in methane production. Which corrective action is most
appropriate?
A. Increase the sludge feed rate to dilute the volatile acids.
B. Add lime to raise the pH to 7.0 and continue feeding.
C. Stop feeding, reduce mixing, and allow the methanogens to recover.
D. Increase the digester temperature to thermophilic range to accelerate
digestion.
Correct Answer: C - Stop feeding, reduce mixing, and allow the
methanogens to recover.
RATIONALE
The symptoms indicate acid accumulation and methanogen inhibition.
The standard remedy is to stop or reduce feeding, minimize mixing to
prevent oxygen intrusion, and allow the methanogen population to
recover. Adding lime may temporarily raise pH but does not address
the volatile acid buildup; increasing feed or temperature would
exacerbate the imbalance.
Question 5
A biosolids land application site is subject to the aggregate cumulative loading
rate for copper under 40 CFR Part 503. If the soil already has 750 lb/acre of
copper from previous applications and the regulatory limit is 1,500 lb/acre,
what is the maximum additional copper that can be applied?
A. 750 lb/acre
B. 1,500 lb/acre
C. 0 lb/acre
D. 2,250 lb/acre
Correct Answer: A - 750 lb/acre
Page 4
