FRWA WWTP OPERATOR EXAM 180 QUESTIONS &
CORRECT ANSWERS LATEST 2026/2027
A wastewater plant has a clarifier that is 90 ft. X 45 ft. X 10 ft. Plant flow is
965,000 gallons per day. The influent to the clarifier has a BOD of 145 mg/L.
What is the surface loading of the clarifier in gal/day/sq. ft.? - ANSWER-238
You have hooked up a one-ton chlorine cylinder in you plant. The pressure gauge
on the manifold line indicates good pressure, but you are unable to obtain the
maximum feed rate from the chlorinator. What is the probable cause of this
situation? - ANSWER-The chlorination system has vacuum leaks at the joints,
gaskets or tubing
You have just been hired as lead operator at a plant that has been online
approximately 2 years. It has met all regulatory requirements, but recently the
coliform counts have been steadily increasing. The cause is probably due to: -
ANSWER-A gradual build-up of solids in the chlorine contact chamber
A chlorinator with automatic, proportionate flow controls will not feed enough
chlorine to produce a proper chlorine residual. Sampling shows that at some hours
of the day, there is an adequate residual, but there are times during the day of
insufficient chlorine residual. What is the probable cause? - ANSWER-Automatic
control device is malfunctioning
You plant's coliform count in the effluent has failed to meet the required regulatory
standards for disinfection. You have checked the supply and found this is not the
problem. What is the probable cause? - ANSWER-The contact time is too short in
the contact chamber
,Low DO levels, nutrient deficiencies, and low pH will favor the growth of: -
ANSWER-Filaments
Activated sludge is an aerobic process where microorganisms require the presence
of DO in order to feed, grow, and multiply. The DO in the aeration tank must be
kept between _____ to maintain a healthy effluent. - ANSWER-1.0-3.0 ppm
Of the activated sludge modifications, which process has a detention time of 24
hours in the aeration basin? - ANSWER-Extended aeration
Sludge is floating to the surface of the secondary clarifier of an activated sludge
plant. The foam in the aeration tank has changed in color and consistency, and DO
levels are dropping at a rapid rate. What is the probable cause? - ANSWER-An
increase in the denitrification rate
You observe the following conditions in your plant: low DO levels in the aeration
tank, low pH of the mixed liquor, and SVI is high. The settleometer indicates slow
settling leaving clear supernatant. A microscopic examination reveals numerous
filamentous organisms. What is the probable cause? - ANSWER-Biological
bulking
You are operating an activated sludge plant. Effluent BOD ranges from 3-5 ppm,
and effluent DO ranges from 1.5-2.5 ppm. The sludge blanket is 1-2 ft. deep. A
toxic load entered the plant on Sunday. On Monday, you observe the secondary
clarifier effluent is cloudy, and plant effluent is poor. What should you do? -
ANSWER-Check for inactive protozoa, stop wasting and return all solids to the
aerator
, In the contact stabilization mode of the activated sludge process, the _____ is
where bugs digest the food and then are returned hungry to the original aeration
tank ready to eat more food. - ANSWER-Reaeration tank
Successful trickling filter operation depends on: - ANSWER-Maintaining a good
growth of organisms on the filter media
In the winter, the temperature of the wastewater applied to a trickling filter is lower
than it is in the summer. This may cause: - ANSWER-A decrease in the amount of
BOD removed from the wastewater
pH in the aerobic digester has dropped to 6.0. Concrete walls are showing signs of
discoloration. What is the probable cause? - ANSWER-Nitrification is occurring
and wastewater alkalinity is low
The key indicator of how well the anaerobic sludge digestion process is
functioning is the: - ANSWER-Volatile acid to alkalinity relationship
When ponding occurs on a biological growth system, what effect does this have on
the plant effluent? - ANSWER-It will cause lower BOD removal efficiencies for
the unit
According to Chapter 62-600, Domestic Wastewater Facilities, secondary
treatment effluent limitation plants shall be designed to achieve an effluent after
disinfection containing no more than: - ANSWER-20 ppm BOD and 20 ppm TSS
or 90% removal of each
According to Chapter 62-600, Domestic Wastewater Facilities, where chlorine is
used for disinfection, maintenance of_____ is required for the basic level of
CORRECT ANSWERS LATEST 2026/2027
A wastewater plant has a clarifier that is 90 ft. X 45 ft. X 10 ft. Plant flow is
965,000 gallons per day. The influent to the clarifier has a BOD of 145 mg/L.
What is the surface loading of the clarifier in gal/day/sq. ft.? - ANSWER-238
You have hooked up a one-ton chlorine cylinder in you plant. The pressure gauge
on the manifold line indicates good pressure, but you are unable to obtain the
maximum feed rate from the chlorinator. What is the probable cause of this
situation? - ANSWER-The chlorination system has vacuum leaks at the joints,
gaskets or tubing
You have just been hired as lead operator at a plant that has been online
approximately 2 years. It has met all regulatory requirements, but recently the
coliform counts have been steadily increasing. The cause is probably due to: -
ANSWER-A gradual build-up of solids in the chlorine contact chamber
A chlorinator with automatic, proportionate flow controls will not feed enough
chlorine to produce a proper chlorine residual. Sampling shows that at some hours
of the day, there is an adequate residual, but there are times during the day of
insufficient chlorine residual. What is the probable cause? - ANSWER-Automatic
control device is malfunctioning
You plant's coliform count in the effluent has failed to meet the required regulatory
standards for disinfection. You have checked the supply and found this is not the
problem. What is the probable cause? - ANSWER-The contact time is too short in
the contact chamber
,Low DO levels, nutrient deficiencies, and low pH will favor the growth of: -
ANSWER-Filaments
Activated sludge is an aerobic process where microorganisms require the presence
of DO in order to feed, grow, and multiply. The DO in the aeration tank must be
kept between _____ to maintain a healthy effluent. - ANSWER-1.0-3.0 ppm
Of the activated sludge modifications, which process has a detention time of 24
hours in the aeration basin? - ANSWER-Extended aeration
Sludge is floating to the surface of the secondary clarifier of an activated sludge
plant. The foam in the aeration tank has changed in color and consistency, and DO
levels are dropping at a rapid rate. What is the probable cause? - ANSWER-An
increase in the denitrification rate
You observe the following conditions in your plant: low DO levels in the aeration
tank, low pH of the mixed liquor, and SVI is high. The settleometer indicates slow
settling leaving clear supernatant. A microscopic examination reveals numerous
filamentous organisms. What is the probable cause? - ANSWER-Biological
bulking
You are operating an activated sludge plant. Effluent BOD ranges from 3-5 ppm,
and effluent DO ranges from 1.5-2.5 ppm. The sludge blanket is 1-2 ft. deep. A
toxic load entered the plant on Sunday. On Monday, you observe the secondary
clarifier effluent is cloudy, and plant effluent is poor. What should you do? -
ANSWER-Check for inactive protozoa, stop wasting and return all solids to the
aerator
, In the contact stabilization mode of the activated sludge process, the _____ is
where bugs digest the food and then are returned hungry to the original aeration
tank ready to eat more food. - ANSWER-Reaeration tank
Successful trickling filter operation depends on: - ANSWER-Maintaining a good
growth of organisms on the filter media
In the winter, the temperature of the wastewater applied to a trickling filter is lower
than it is in the summer. This may cause: - ANSWER-A decrease in the amount of
BOD removed from the wastewater
pH in the aerobic digester has dropped to 6.0. Concrete walls are showing signs of
discoloration. What is the probable cause? - ANSWER-Nitrification is occurring
and wastewater alkalinity is low
The key indicator of how well the anaerobic sludge digestion process is
functioning is the: - ANSWER-Volatile acid to alkalinity relationship
When ponding occurs on a biological growth system, what effect does this have on
the plant effluent? - ANSWER-It will cause lower BOD removal efficiencies for
the unit
According to Chapter 62-600, Domestic Wastewater Facilities, secondary
treatment effluent limitation plants shall be designed to achieve an effluent after
disinfection containing no more than: - ANSWER-20 ppm BOD and 20 ppm TSS
or 90% removal of each
According to Chapter 62-600, Domestic Wastewater Facilities, where chlorine is
used for disinfection, maintenance of_____ is required for the basic level of
