(PART 1) GRADE 4 WASTEWATER
CERTIFICATION PRACTICE TEST 2025
VERIFIED STUDY QUESTIONS AND
ANSWERS
What is the odor detection limit of chlorine gas?
a. 0.1 ppm b. 0.3 ppm c. 0.5 ppm d. 1.0 ppm - ANSWER-b. 0.3 ppm
What is a cathode?
a. negative pole of an electrolyte b. positive pole of an electrolyte c. negative pole of an
electrolytic cell or system d. positive pole of an electrolytic cell or system - ANSWER-
negative pole of an electrolytic cell or system
The least reactive metals are called a. anodic metals b. galvanic metals c. cathodic
metals d. tempered metals - ANSWER-c. cathodic metals
Unless water cooled, the operating temperature of a mechanical seal in a pump should
never exceed a. 95°F (35°C) b. 120°F (49°C) c. 140°F (60°C) d. 160°F (71°C) -
ANSWER-d. 160°F (71°C)
What term describes the condition that exists when the source of the water supply is
below the centerline of the pump? a. total discharge head b. suction lift c. velocity head
d. pressure head - ANSWER-b. suction lift
All occupied trenches 4 or more ft deep must provide exits at a. 15-ft intervals b. 20-ft
intervals c. 25-ft intervals d. 30-ft intervals - ANSWER-c. 25-ft intervals
What is the difference between a weak acid and a strong acid? a. amount of buffering
released b. amount of hydroxyl ions released c. amount of carbonate ions released d.
amount of hydrogen ions released - ANSWER-d. amount of hydrogen ions released
Which one of the following is the best type of valve to use to dampen a water hammer?
a. needle b. pressure-relief c. pressure-reducing d. pinch - ANSWER-b. pressure-relief
A shock load of toxic wastes coming into a plant can be treated or controlled with
a. coagulants only b. coagulants and lime c. coagulants and coagulant aid d. coagulants
or chlorine - ANSWER-d. coagulants or chlorine
Toxic solids should be disposed of in
,a. a digester to destabilize and break down the toxins b. an approved sanitary landfill c.
an incinerator d. a sludge pond for further aerobic breakdown - ANSWER-b. an
approved sanitary landfill
Which one of the following best defines the term stray-current corrosion?
a. decomposition of a metal by its reaction with an acidic water b. decomposition of a
material caused by an outside electric current c. reaction between a metal and water d.
reaction between two different metals with water acting as an electrolyte - ANSWER-b.
decomposition of a material caused by an outside electric current
On startup of a small package wastewater treatment plant, lime should be added to the
digestion unit when the pH goes below
a. 6.8 b. 7.0 c. 7.2 d. 7.5 - ANSWER-b. 7.0
If the effluent to a small package wastewater treatment plant using the activated sludge
process appears turbid, what is most probably the cause?
a. low concentration of dissolved oxygen (DO) in the aeration tank b. pumping rate for
the return of activated sludge is out of balance c. excessive aeration rates in the
aeration tank d. alkalinity is too high - ANSWER-b. pumping rate for the return of
activated sludge is out of balance
If a small package treatment plant utilizing the activated sludge process has a
lightcolored floating sludge on the surface of the clarifier, which one of the following
would most likely eliminate the floating sludge?
a. increase the sludge wasting rate b. add a pH stabilizer, as pH is too low c. reduce the
aeration rates d. increase the return sludge rate - ANSWER-c. reduce the aeration rates
What usually causes frothing in the activated sludge process?
a. too low a solids level b. too high a solids leaving c. too short a retention time d. too
long a detention time - ANSWER-d. too long a detention time
Which one of the following suggestions would most likely control foaming?
, a. increase the detention time b. water sprays c. increase the dissolved oxygen d.
increase solids wasting - ANSWER-b. water sprays
What is the ideal level of solids in a jar test sample collected from an aeration tank if it is
allowed to settle for 30 min?
a. ¼ of the jar depth b. ⅓ of the jar depth c. ⅖ of the jar depth d. ½ of the jar depth -
ANSWER-d. ½ of the jar depth
In a small wastewater treatment plant using the activated sludge process, solids in the
settling compartment should not be allowed to remain longer than
a. 2 hr b. 3 hr c. 4 hr d. 5 hr - ANSWER-a. 2 hr
In an oxidation ditch, what would cause a dark gray color to develop in the mixed liquor?
a. the buildup of facultative bacteria b. the buildup of aerobic bacteria c. the buildup of
anaerobic bacteria d. the lack of bacteria buildup - ANSWER-d. the lack of bacteria
buildup
During the startup of the oxidation sludge process in the oxidation ditch, the operator
should maintain the highest
a. recommended level of dissolved oxygen b. inflow of raw wastewater possible in order
to fill the ditch c. possible rate of returned activated sludge d. possible brush rotor speed
advisable - ANSWER-c. possible rate of returned activated sludge
What is the best range of dissolved oxygen in an oxidation ditch for optimum operation?
a. 0.5 to 2.0 mg/L b. 1.0 to 2.0 mg/L c. 1.0 to 2.5 mg/L d. 1.0 to 3.0 mg/L - ANSWER-a.
0.5 to 2.0 mg/L
Overoxidation of an oxidation ditch will cause
a. an algae bloom b. suspended solids to float c. oxygen toxicity for protozoans and
other organisms, especially rotifers d. the formation of pinpoint floc - ANSWER-d. the
formation of pinpoint floc
CERTIFICATION PRACTICE TEST 2025
VERIFIED STUDY QUESTIONS AND
ANSWERS
What is the odor detection limit of chlorine gas?
a. 0.1 ppm b. 0.3 ppm c. 0.5 ppm d. 1.0 ppm - ANSWER-b. 0.3 ppm
What is a cathode?
a. negative pole of an electrolyte b. positive pole of an electrolyte c. negative pole of an
electrolytic cell or system d. positive pole of an electrolytic cell or system - ANSWER-
negative pole of an electrolytic cell or system
The least reactive metals are called a. anodic metals b. galvanic metals c. cathodic
metals d. tempered metals - ANSWER-c. cathodic metals
Unless water cooled, the operating temperature of a mechanical seal in a pump should
never exceed a. 95°F (35°C) b. 120°F (49°C) c. 140°F (60°C) d. 160°F (71°C) -
ANSWER-d. 160°F (71°C)
What term describes the condition that exists when the source of the water supply is
below the centerline of the pump? a. total discharge head b. suction lift c. velocity head
d. pressure head - ANSWER-b. suction lift
All occupied trenches 4 or more ft deep must provide exits at a. 15-ft intervals b. 20-ft
intervals c. 25-ft intervals d. 30-ft intervals - ANSWER-c. 25-ft intervals
What is the difference between a weak acid and a strong acid? a. amount of buffering
released b. amount of hydroxyl ions released c. amount of carbonate ions released d.
amount of hydrogen ions released - ANSWER-d. amount of hydrogen ions released
Which one of the following is the best type of valve to use to dampen a water hammer?
a. needle b. pressure-relief c. pressure-reducing d. pinch - ANSWER-b. pressure-relief
A shock load of toxic wastes coming into a plant can be treated or controlled with
a. coagulants only b. coagulants and lime c. coagulants and coagulant aid d. coagulants
or chlorine - ANSWER-d. coagulants or chlorine
Toxic solids should be disposed of in
,a. a digester to destabilize and break down the toxins b. an approved sanitary landfill c.
an incinerator d. a sludge pond for further aerobic breakdown - ANSWER-b. an
approved sanitary landfill
Which one of the following best defines the term stray-current corrosion?
a. decomposition of a metal by its reaction with an acidic water b. decomposition of a
material caused by an outside electric current c. reaction between a metal and water d.
reaction between two different metals with water acting as an electrolyte - ANSWER-b.
decomposition of a material caused by an outside electric current
On startup of a small package wastewater treatment plant, lime should be added to the
digestion unit when the pH goes below
a. 6.8 b. 7.0 c. 7.2 d. 7.5 - ANSWER-b. 7.0
If the effluent to a small package wastewater treatment plant using the activated sludge
process appears turbid, what is most probably the cause?
a. low concentration of dissolved oxygen (DO) in the aeration tank b. pumping rate for
the return of activated sludge is out of balance c. excessive aeration rates in the
aeration tank d. alkalinity is too high - ANSWER-b. pumping rate for the return of
activated sludge is out of balance
If a small package treatment plant utilizing the activated sludge process has a
lightcolored floating sludge on the surface of the clarifier, which one of the following
would most likely eliminate the floating sludge?
a. increase the sludge wasting rate b. add a pH stabilizer, as pH is too low c. reduce the
aeration rates d. increase the return sludge rate - ANSWER-c. reduce the aeration rates
What usually causes frothing in the activated sludge process?
a. too low a solids level b. too high a solids leaving c. too short a retention time d. too
long a detention time - ANSWER-d. too long a detention time
Which one of the following suggestions would most likely control foaming?
, a. increase the detention time b. water sprays c. increase the dissolved oxygen d.
increase solids wasting - ANSWER-b. water sprays
What is the ideal level of solids in a jar test sample collected from an aeration tank if it is
allowed to settle for 30 min?
a. ¼ of the jar depth b. ⅓ of the jar depth c. ⅖ of the jar depth d. ½ of the jar depth -
ANSWER-d. ½ of the jar depth
In a small wastewater treatment plant using the activated sludge process, solids in the
settling compartment should not be allowed to remain longer than
a. 2 hr b. 3 hr c. 4 hr d. 5 hr - ANSWER-a. 2 hr
In an oxidation ditch, what would cause a dark gray color to develop in the mixed liquor?
a. the buildup of facultative bacteria b. the buildup of aerobic bacteria c. the buildup of
anaerobic bacteria d. the lack of bacteria buildup - ANSWER-d. the lack of bacteria
buildup
During the startup of the oxidation sludge process in the oxidation ditch, the operator
should maintain the highest
a. recommended level of dissolved oxygen b. inflow of raw wastewater possible in order
to fill the ditch c. possible rate of returned activated sludge d. possible brush rotor speed
advisable - ANSWER-c. possible rate of returned activated sludge
What is the best range of dissolved oxygen in an oxidation ditch for optimum operation?
a. 0.5 to 2.0 mg/L b. 1.0 to 2.0 mg/L c. 1.0 to 2.5 mg/L d. 1.0 to 3.0 mg/L - ANSWER-a.
0.5 to 2.0 mg/L
Overoxidation of an oxidation ditch will cause
a. an algae bloom b. suspended solids to float c. oxygen toxicity for protozoans and
other organisms, especially rotifers d. the formation of pinpoint floc - ANSWER-d. the
formation of pinpoint floc
