TX CLASS C WASTEWATER
TREATMENT LICENSE EXAM 2025
LATEST QUESTIONS AND DETAILED
CORRECT ANSWERS| ALREADY
GRADED A+
A conventional activated sludge process has primary
clarifiers that remove about ________ percent of the
organic load.. Correct Answer 30-40%
What activated sludge process parameters can an
operator change directly? Correct Answer aeration rates,
waste rates, and return sludge rates
What happens when the return sludge rate is too low?
Correct Answer there will be insufficient organisms to treat
the waste load entering the aeration basin and the sludge
blanket in the secondary clarifier could become too high
Physical causes of sludge bulking are... Correct Answer
excessive hydraulic loading, settled sludge that is not
promptly removed from the clarifier, inadequate weir
lengths and improper ratio of depth to surface area of the
final clarifier
SVI Formula
(Sludge Volume Index) Correct Answer 30 min settle
test/MLSS x 1000
,Normal range for SVI (sludge volume index) Correct
Answer 70-150
What DO levels (in aeration) are optimal to maintain health
of aerobic microorganisms? Correct Answer 2-4 mg/L
How deep should the clarifier blanket be? Correct Answer
filling the bottom 1/4
Weir loadings should not exceed _________ gal/day/linear
foot of weir at peak flow (1 MGD or less plant). Correct
Answer 20,000
Weir loadings should not exceed ___________
gal/day/linear foot of weir at peak flow (1 MGD or above
plant). Correct Answer 30,000
Is activated sludge aerobic or anaerobic? Correct Answer
aerobic
Why do pumps continually send RAS to the aeration tank?
Correct Answer to reseed the biological reaction in the
aeration tank and remove accumulating sludge from the
clarifier
How much raw influent should return pumps be able to
provide? Correct Answer 50-150%
For an activated sludge process to work properly, an
operator much insure that... Correct Answer enough return
activated sludge is sent tot he aerator to maintain the
, process; solids do not accumulate in the clarifier; excess
solids that develop in the process are removed frequently
enough to avoid build-up
During normal operations, the __________ will
concentrate sludge, making it 2-4 times denser than that
of the mixed liquor. Correct Answer clarifier
Define F/M ratio Correct Answer food to microorganism
ratio
How is F/M ratio calculated? Correct Answer by dividing
the pounds of incoming BOD (food) by the pounds of
MLVSS (microorganisms) in the aeration tank
What conditions should an operator observe in a well
controlled activated sludge process? Correct Answer
surface turbulence/uniform roll pattern; foam/small amount
of light-colored, crisp foam; odors/mild, earthy;
color/medium-brown
What conditions should an operator observe in a well
controlled clarifier? Correct Answer very little surface
scum; a sludge blanket covering 1/4 of the bottom; uniform
weir flow (all the way around); almost no rising solids and
overflow should be clear and free of floc
What type solids cannot go onto a trickling filter? Correct
Answer large suspended solids
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