(Part 1) Grade 4 wastewater certification
practice test questions and answers with solutions
2026/2026
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?
practice test questions and answers with solutions
2026/2026
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?
