WASTEWATER TREATMENT OPERATOR CERTIFICATION
EXAM NEWEST 2026 ACTUAL EXAM TEST BANK|
COMPLETE 350 REAL EXAM QUESTIONS AND
CORRECT VERIFIED ANSWERS/ GRADED A+ (BRAND
NEW!!)
1. A bar screen with 1-inch openings is most effective at
removing which of the following?
a) Colloidal solids
b) Dissolved solids
c) Large rags and debris
d) Settleable organic solids
Answer: c) Large rags and debris
Rationale: Bar screens are coarse screens (typically 0.5–2
inches) designed to protect pumps and downstream equipment
from large debris. Colloidal and dissolved solids pass through;
settleable solids require primary clarifiers.
1
,2. What is the primary purpose of a grit chamber?
a) Remove floating scum
b) Remove inorganic, heavy particles like sand and gravel
c) Remove BOD from wastewater
d) Disinfect the wastewater
Answer: b) Remove inorganic, heavy particles like sand and
gravel
Rationale: Grit chambers use velocity control or aeration to
settle out dense inorganic materials (sand, eggshells, coffee
grounds) that would otherwise abrade pumps and accumulate in
digesters.
3. A primary clarifier typically removes what percentage of
total suspended solids (TSS) under normal operation?
a) 10–20%
b) 30–40%
2
,c) 50–65%
d) 85–95%
Answer: c) 50–65%
Rationale: Primary clarifiers are designed for sedimentation.
Typical removal efficiencies are 50–65% TSS and 25–35%
BOD. The remaining solids are treated in secondary processes.
4. Excessive flow velocity in a rectangular primary clarifier
can cause:
a) Improved settling
b) Hydraulic short-circuiting and solids carry-over
c) Complete denitrification
d) Increased sludge compaction
Answer: b) Hydraulic short-circuiting and solids carry-over
Rationale: High velocity reduces detention time and creates
turbulence, preventing settling. Short-circuiting allows solids to
exit with the effluent, reducing treatment efficiency.
3
, 5. Floating scum on a primary clarifier is typically removed
by:
a) A bottom scraper
b) A surface skimmer or flight collector
c) A centrifugal pump
d) A bar screen
Answer: b) A surface skimmer or flight collector
Rationale: Scum (grease, oil, light solids) floats and is skimmed
from the surface using rotating flights or a scum trough. Bottom
scrapers remove settled sludge.
6. What happens if primary sludge is left in the clarifier too
long (septic conditions)?
a) Sludge becomes easier to dewater
b) Sludge produces methane and rises to the surface (rising
sludge)
4
EXAM NEWEST 2026 ACTUAL EXAM TEST BANK|
COMPLETE 350 REAL EXAM QUESTIONS AND
CORRECT VERIFIED ANSWERS/ GRADED A+ (BRAND
NEW!!)
1. A bar screen with 1-inch openings is most effective at
removing which of the following?
a) Colloidal solids
b) Dissolved solids
c) Large rags and debris
d) Settleable organic solids
Answer: c) Large rags and debris
Rationale: Bar screens are coarse screens (typically 0.5–2
inches) designed to protect pumps and downstream equipment
from large debris. Colloidal and dissolved solids pass through;
settleable solids require primary clarifiers.
1
,2. What is the primary purpose of a grit chamber?
a) Remove floating scum
b) Remove inorganic, heavy particles like sand and gravel
c) Remove BOD from wastewater
d) Disinfect the wastewater
Answer: b) Remove inorganic, heavy particles like sand and
gravel
Rationale: Grit chambers use velocity control or aeration to
settle out dense inorganic materials (sand, eggshells, coffee
grounds) that would otherwise abrade pumps and accumulate in
digesters.
3. A primary clarifier typically removes what percentage of
total suspended solids (TSS) under normal operation?
a) 10–20%
b) 30–40%
2
,c) 50–65%
d) 85–95%
Answer: c) 50–65%
Rationale: Primary clarifiers are designed for sedimentation.
Typical removal efficiencies are 50–65% TSS and 25–35%
BOD. The remaining solids are treated in secondary processes.
4. Excessive flow velocity in a rectangular primary clarifier
can cause:
a) Improved settling
b) Hydraulic short-circuiting and solids carry-over
c) Complete denitrification
d) Increased sludge compaction
Answer: b) Hydraulic short-circuiting and solids carry-over
Rationale: High velocity reduces detention time and creates
turbulence, preventing settling. Short-circuiting allows solids to
exit with the effluent, reducing treatment efficiency.
3
, 5. Floating scum on a primary clarifier is typically removed
by:
a) A bottom scraper
b) A surface skimmer or flight collector
c) A centrifugal pump
d) A bar screen
Answer: b) A surface skimmer or flight collector
Rationale: Scum (grease, oil, light solids) floats and is skimmed
from the surface using rotating flights or a scum trough. Bottom
scrapers remove settled sludge.
6. What happens if primary sludge is left in the clarifier too
long (septic conditions)?
a) Sludge becomes easier to dewater
b) Sludge produces methane and rises to the surface (rising
sludge)
4
