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Iowa Wastewater Operator Grade IV Exam ACTUAL
VERIFIED EXAM QUESTIONS AND VERIFIED
ANSWERS WITH RATIONALES|| NEWEST EXAM!!!
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?
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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
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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?
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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
Iowa Wastewater Operator Grade IV Exam ACTUAL
VERIFIED EXAM QUESTIONS AND VERIFIED
ANSWERS WITH RATIONALES|| NEWEST EXAM!!!
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?
,2|Page
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
,3|Page
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?
, 4|Page
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
