ABC WASTEWATER LEVEL 3 CERTIFICATION EXAM - GENERAL | FREQUENTLY
TESTED QUESTIONS WITH CORRECT ANSWERS | BRAND NEW!
Question 1
Turbidity in wastewater is caused by:
A) Excessive color from industrial dyes
B) Dissolved calcium concentrations
C) Total hardness of the water
D) Finely divided suspended material
E) High concentrations of dissolved oxygen
Correct Answer: D) finely divided suspended material
Rationale: Turbidity is a measure of the cloudiness or haziness of a fluid caused by large
numbers of individual particles that are generally invisible to the naked eye. In wastewater,
this is primarily composed of finely divided suspended solids, organic matter, and
microscopic organisms. Color and dissolved minerals (like calcium/hardness) do not
typically contribute to turbidity readings as they do not scatter light in the same way
suspended particles do.
Question 2
The gas most commonly associated with septic wastewater is:
A) Carbon dioxide
B) Carbon monoxide
C) Hydrogen sulfide
D) Methane
E) Nitrogen dioxide
Correct Answer: C) hydrogen sulfide
Rationale: Septic wastewater is characterized by anaerobic conditions (lack of oxygen). In
this environment, sulfur-reducing bacteria break down organic sulfates into hydrogen
sulfide (H2S). H2S is famous for its "rotten egg" odor and is highly corrosive to concrete
and metal, as well as being extremely toxic to humans at high concentrations.
Question 3
How many cubic meters per second are in 10 MGD (Million Gallons per Day)?
A) 0.44
B) 1.44
C) 4.73
D) 24.62
E) 43.81
Correct Answer: A) 0.44
Rationale: To convert 10 MGD to m³/s: First, convert MGD to Gallons per minute
(10,000,,440 = 6,944 gpm). Then convert gallons to cubic meters (1 gal = 0.003785
m³). 6,944 gpm * 0.003785 = 26.28 m³/min. Finally, divide by 60 seconds (26. = 0.438).
Rounding to the nearest hundredth gives 0.44 m³/s.
, 2
Question 4
Mechanical ventilation of a lift station is required to:
A) Lower temperatures to reduce the proportion of hydrogen sulfide
B) Reduce chlorine demand in the collection system
C) Reduce corrosion of structures and equipment
D) Increase dissolved oxygen in raw wastewater
E) Prevent the growth of filamentous bacteria
Correct Answer: C) reduce corrosion
Rationale: Hydrogen sulfide gas (H2S) in a lift station reacts with moisture on surfaces to
form sulfuric acid, which is highly corrosive to metal pipes and concrete walls. Mechanical
ventilation exhausts these corrosive gases and reduces the humidity/moisture accumulation,
thereby extending the life of the infrastructure and providing a safer environment for
operators.
Question 5
A wet well probe is usually used for ________ determination(s) of level.
A) Approximate
B) Dual point
C) Continuous
D) Single point
E) Ultrasonic
Correct Answer: D) single point
Rationale: A standard level probe (like a conductivity probe or a float switch) acts as a
"point" sensor. It sends a signal only when the water level reaches that specific height (e.g.,
"Pump On" or "High Level Alarm"). In contrast, ultrasonic or pressure transducers
provide "continuous" level determination, tracking the level at every inch of the tank.
Question 6
A pump is delivering at less than the expected rate of discharge. Which of the causes listed below
is incorrect?
A) Speed of motor too low
B) Pump not primed
C) Impeller clogged
D) Discharge head too low
E) Air leak in suction line
Correct Answer: D) discharge head too low
Rationale: If the discharge head were "too low," the pump would actually deliver more flow
than expected because it has less resistance to overcome (following the pump curve). Low
discharge rates are caused by high head, clogs, low speeds, or mechanical failures like a
worn impeller or air binding.
, 3
Question 7
Metal pipes often fail because of:
A) Back siphonage
B) Browning movement
C) Galvanic action
D) Reverse osmosis
E) Cavitation
Correct Answer: C) galvanic action
Rationale: Galvanic action occurs when two dissimilar metals are in contact in the presence
of an electrolyte (wastewater). This creates a battery-like effect where one metal (the
anode) corrodes at an accelerated rate to protect the other (the cathode). This is a primary
cause of localized pitting and failure in metal pipe systems.
Question 8
When a fire hydrant is operated, it should be:
A) Just opened enough to have a flow
B) Opened fully
C) Opened halfway
D) Regulated to the flow required for the task
E) Opened only with a standard pipe wrench
Correct Answer: B) opened fully
Rationale: Fire hydrants are designed with a "drain hole" at the base. When the hydrant is
only partially opened, the drain hole may remain open, allowing high-pressure water to
wash away the soil/bedding around the base of the hydrant (undermining it). Opening it
fully ensures the drain hole is completely sealed and the valve is seated correctly.
Question 9
If the pump bearings on horizontal centrifugal pumps are over-lubricated, the most important
effect is that the:
A) Extra lubricant will result in smoother operation
B) Extra lubricant will not make any difference
C) Extra lubricant will be wasted but harmless
D) Shaft or shaft sleeve will be damaged due to heat
E) Impeller will lose its balance
Correct Answer: D) shaft or shaft sleeve will be damaged
Rationale: Over-lubrication is a common cause of bearing failure. Too much grease causes
the rolling elements to "plow" through the grease rather than roll over a thin film. This
creates friction and heat, which can lead to bearing seizure, thinning of the lubricant, and
eventual damage to the pump shaft or sleeves.
, 4
Question 10
If packing is not maintained properly, which of the following will occur?
A) Cavitation damage to the impeller
B) The impeller will corrode prematurely
C) Loss of suction due to air being allowed to enter the pump
D) The discharge head will increase
E) The motor will spin in reverse
Correct Answer: C) loss of suction due to air being allowed to enter pump
Rationale: Packing is designed to seal the point where the shaft enters the pump casing. It
requires a slight "leak" of water for lubrication/cooling. If it dries out or is too loose, air
can be sucked into the pump (especially in suction-lift applications), causing the pump to
lose its prime or experience diminished performance due to air binding.
Question 11
Air flow through a trickling filter when the influent is warmer than the air temperature is:
A) Upward through the filter
B) Downward through the filter
C) Inadequate and may require forced air ventilation
D) Improved by decreasing the recirculation
E) Stagnant due to density equalization
Correct Answer: A) upward through the filter
Rationale: This is due to the "chimney effect." Warmer wastewater heats the air inside the
filter media. Warm air is less dense and rises, creating a natural upward draft. This natural
ventilation is crucial for providing oxygen to the microorganisms (zoogloeal film) living on
the filter media.
Question 12
An active sludge in the aeration tank with an abundant available food supply will have a
relatively:
A) High oxygen uptake and fast settling rate
B) High oxygen uptake and slow settling rate
C) Low oxygen uptake and fast settling rate
D) Low oxygen uptake and slow settling rate
E) High alkalinity and low pH
Correct Answer: B) high oxygen uptake and slow settling rate
Rationale: In a high F/M (Food to Microorganism) environment, bacteria are in the "log
growth phase." They are highly active and consuming oxygen rapidly (high uptake).
However, because they are dispersed and not yet forming heavy flocs (which occurs in the
"endogenous respiration" phase), the sludge remains light and settles slowly. This is often
associated with "young sludge."
TESTED QUESTIONS WITH CORRECT ANSWERS | BRAND NEW!
Question 1
Turbidity in wastewater is caused by:
A) Excessive color from industrial dyes
B) Dissolved calcium concentrations
C) Total hardness of the water
D) Finely divided suspended material
E) High concentrations of dissolved oxygen
Correct Answer: D) finely divided suspended material
Rationale: Turbidity is a measure of the cloudiness or haziness of a fluid caused by large
numbers of individual particles that are generally invisible to the naked eye. In wastewater,
this is primarily composed of finely divided suspended solids, organic matter, and
microscopic organisms. Color and dissolved minerals (like calcium/hardness) do not
typically contribute to turbidity readings as they do not scatter light in the same way
suspended particles do.
Question 2
The gas most commonly associated with septic wastewater is:
A) Carbon dioxide
B) Carbon monoxide
C) Hydrogen sulfide
D) Methane
E) Nitrogen dioxide
Correct Answer: C) hydrogen sulfide
Rationale: Septic wastewater is characterized by anaerobic conditions (lack of oxygen). In
this environment, sulfur-reducing bacteria break down organic sulfates into hydrogen
sulfide (H2S). H2S is famous for its "rotten egg" odor and is highly corrosive to concrete
and metal, as well as being extremely toxic to humans at high concentrations.
Question 3
How many cubic meters per second are in 10 MGD (Million Gallons per Day)?
A) 0.44
B) 1.44
C) 4.73
D) 24.62
E) 43.81
Correct Answer: A) 0.44
Rationale: To convert 10 MGD to m³/s: First, convert MGD to Gallons per minute
(10,000,,440 = 6,944 gpm). Then convert gallons to cubic meters (1 gal = 0.003785
m³). 6,944 gpm * 0.003785 = 26.28 m³/min. Finally, divide by 60 seconds (26. = 0.438).
Rounding to the nearest hundredth gives 0.44 m³/s.
, 2
Question 4
Mechanical ventilation of a lift station is required to:
A) Lower temperatures to reduce the proportion of hydrogen sulfide
B) Reduce chlorine demand in the collection system
C) Reduce corrosion of structures and equipment
D) Increase dissolved oxygen in raw wastewater
E) Prevent the growth of filamentous bacteria
Correct Answer: C) reduce corrosion
Rationale: Hydrogen sulfide gas (H2S) in a lift station reacts with moisture on surfaces to
form sulfuric acid, which is highly corrosive to metal pipes and concrete walls. Mechanical
ventilation exhausts these corrosive gases and reduces the humidity/moisture accumulation,
thereby extending the life of the infrastructure and providing a safer environment for
operators.
Question 5
A wet well probe is usually used for ________ determination(s) of level.
A) Approximate
B) Dual point
C) Continuous
D) Single point
E) Ultrasonic
Correct Answer: D) single point
Rationale: A standard level probe (like a conductivity probe or a float switch) acts as a
"point" sensor. It sends a signal only when the water level reaches that specific height (e.g.,
"Pump On" or "High Level Alarm"). In contrast, ultrasonic or pressure transducers
provide "continuous" level determination, tracking the level at every inch of the tank.
Question 6
A pump is delivering at less than the expected rate of discharge. Which of the causes listed below
is incorrect?
A) Speed of motor too low
B) Pump not primed
C) Impeller clogged
D) Discharge head too low
E) Air leak in suction line
Correct Answer: D) discharge head too low
Rationale: If the discharge head were "too low," the pump would actually deliver more flow
than expected because it has less resistance to overcome (following the pump curve). Low
discharge rates are caused by high head, clogs, low speeds, or mechanical failures like a
worn impeller or air binding.
, 3
Question 7
Metal pipes often fail because of:
A) Back siphonage
B) Browning movement
C) Galvanic action
D) Reverse osmosis
E) Cavitation
Correct Answer: C) galvanic action
Rationale: Galvanic action occurs when two dissimilar metals are in contact in the presence
of an electrolyte (wastewater). This creates a battery-like effect where one metal (the
anode) corrodes at an accelerated rate to protect the other (the cathode). This is a primary
cause of localized pitting and failure in metal pipe systems.
Question 8
When a fire hydrant is operated, it should be:
A) Just opened enough to have a flow
B) Opened fully
C) Opened halfway
D) Regulated to the flow required for the task
E) Opened only with a standard pipe wrench
Correct Answer: B) opened fully
Rationale: Fire hydrants are designed with a "drain hole" at the base. When the hydrant is
only partially opened, the drain hole may remain open, allowing high-pressure water to
wash away the soil/bedding around the base of the hydrant (undermining it). Opening it
fully ensures the drain hole is completely sealed and the valve is seated correctly.
Question 9
If the pump bearings on horizontal centrifugal pumps are over-lubricated, the most important
effect is that the:
A) Extra lubricant will result in smoother operation
B) Extra lubricant will not make any difference
C) Extra lubricant will be wasted but harmless
D) Shaft or shaft sleeve will be damaged due to heat
E) Impeller will lose its balance
Correct Answer: D) shaft or shaft sleeve will be damaged
Rationale: Over-lubrication is a common cause of bearing failure. Too much grease causes
the rolling elements to "plow" through the grease rather than roll over a thin film. This
creates friction and heat, which can lead to bearing seizure, thinning of the lubricant, and
eventual damage to the pump shaft or sleeves.
, 4
Question 10
If packing is not maintained properly, which of the following will occur?
A) Cavitation damage to the impeller
B) The impeller will corrode prematurely
C) Loss of suction due to air being allowed to enter the pump
D) The discharge head will increase
E) The motor will spin in reverse
Correct Answer: C) loss of suction due to air being allowed to enter pump
Rationale: Packing is designed to seal the point where the shaft enters the pump casing. It
requires a slight "leak" of water for lubrication/cooling. If it dries out or is too loose, air
can be sucked into the pump (especially in suction-lift applications), causing the pump to
lose its prime or experience diminished performance due to air binding.
Question 11
Air flow through a trickling filter when the influent is warmer than the air temperature is:
A) Upward through the filter
B) Downward through the filter
C) Inadequate and may require forced air ventilation
D) Improved by decreasing the recirculation
E) Stagnant due to density equalization
Correct Answer: A) upward through the filter
Rationale: This is due to the "chimney effect." Warmer wastewater heats the air inside the
filter media. Warm air is less dense and rises, creating a natural upward draft. This natural
ventilation is crucial for providing oxygen to the microorganisms (zoogloeal film) living on
the filter media.
Question 12
An active sludge in the aeration tank with an abundant available food supply will have a
relatively:
A) High oxygen uptake and fast settling rate
B) High oxygen uptake and slow settling rate
C) Low oxygen uptake and fast settling rate
D) Low oxygen uptake and slow settling rate
E) High alkalinity and low pH
Correct Answer: B) high oxygen uptake and slow settling rate
Rationale: In a high F/M (Food to Microorganism) environment, bacteria are in the "log
growth phase." They are highly active and consuming oxygen rapidly (high uptake).
However, because they are dispersed and not yet forming heavy flocs (which occurs in the
"endogenous respiration" phase), the sludge remains light and settles slowly. This is often
associated with "young sludge."
