Wastewater Exam Class C
The Activated Sludge Process:
A. requires preaeration
B. requires Activated Carbon
C. is an aerobic biological process.
D. Usually precedes primary sedimentation.
E. Requires 50% by volume old sludge to work effectively. - ANS-C. Is an Aerobic
biological process
A complete mix activated sludge plant has a fast settling sludge and high amounts of
pin floc leaving the clarifier. One way to correct this problem is to :
A. Increase the RAS Flow
B. Reduce Wasting Rates
C. Increase dissolved oxygen levels.
D. Increase the F/M ratio by wasting more
E. Increase the sludge age by wasting less. - ANS-D. Increase the F/M Ratio by
Wasting More
Which of the following flow rates should be measured if the operator is to control plant
properly?
A. Aeration rate or resulting dissolved oxygen level.
B. Influent or effluent.
C. return sludge
D. waste sludge
E. all the above - ANS-E. all the above
During start up your aeration tank produces excessive amounts of billowing white foam.
This can be corrected by:
A. Doing nothing, it will go away in a few hours
B. Increasing the sludge wasting rate
C. Seeding the process with sufficient good quality sludge
D. Spraying water on the foam until it is gone
E. Taking a weeks vacation - ANS-C. Seeding the process with sufficient good quality
sludge
,In solving an operational problem at a treatment plant:
A. there is almost always a good technical solution. It may require considerable
experience and time to learn whaat it is.
B. Human errors have to be corrected since the operator is at fault.
C. don't let the laboratory personnel influence you're judgement as to what the best
solution is.
D. standard textbooks in sanitary engineering are the best source of information.
E. It is best to do nothing until the TNRCCC sends a violation notice. - ANS-A. there is
almost always a good technical solution. It may require considerable experience and
time to learn whaat it is.
When the return sludge rate is too low, what happens?
A. the aeration tank will not fill
B. There will be insufficient organisms to treat the wast load entering the aeration basin
C. the activated sludge in the aerator will starve.
D. the sludge blanket in the secondary clarifier could become too high.
E. B and D - ANS-E. B and D
What factors affect how well the mixed liquor suspended solids settle in the final
clarifier?
A. flow velocity and or turbulence
B. temperature
C. quality of the mixed liquor solids
D. Short circuiting
E. All of the above - ANS-E. All of the above
The Active sludge process parameters which n operator can change directly are:
A. aeration rates.
B. waste rates.
C. the ratio of free swimming to stalked ciliates.
D. Return sludge rates.
E. All the above except C. - ANS-E. All the above except C.
Which of the following would you use to increase the degree of nitrification in an
activated sludge plant?
,A. increase the wast rates
B. increase dissolved oxygen levels and increase the sludge age
C. Remove excess alkalinity from the wastewater
D. Maintain a thicker sludge blanket n the clarifier
E. Inhibit the growth of the nitrifying bacteria with chemicals. - ANS-B. increase
dissolved oxygen levels and increase the sludge age
The Maximum change in the sludge wasting rates to maintain uniform operating
conditions should be about
A. 10- 20 % per day
B. 20-40 % per day
C. 40-60 % per day
D. 60-80 % per day
E. 100% per day - ANS-A. 10- 20 % per day
When operating an activated sludge plant, Which TSS concentration is most important
for process control?
A. Primary effluent
B. Aeration tank mixed liquor.
C. Return Sludge
D. Digester.
E. Plant influent - ANS-B. Aeration tank mixed liquor.
How many aeration tanks does a contact stabilization plant have?
A. one, like all the others
B. Four: contact, mix, reaeration and stabilization
C. Two if you count the digester as an aeration tank
D. a contact tank and a reaeration tank
E. none of this makes any sense to me. - ANS-D. a contact tank and a reaeration tank
Reducing the return sludge flow rate for an activated sludge system which has a good
settling sludge will.
A. Decrease the hydraulic detention time in the aeration basin
B. Increase the solids concentration in the aeration basin
C. cause the return sludge concentration to decrease
,D. have no effect on process performance.
E. increase the RAS concentration ad the clarifier blanket thickness. - ANS-E. increase
the RAS concentration ad the clarifier blanket thickness.
What items would you check if an activated sludge plant becomes upset?
A. Influent temperature.
B. Monthly average flow rates
C. BOD loadings MLSS sludge settle-ability D.O. and oxygen uptake rate
D. digester operation. E. Chlorinator settings. - ANS-C. BOD loadings MLSS sludge
settle-ability D.O. and oxygen uptake rate
Causes of sludge bulking include:
A. Low DO and presence of sulfides
B. Air supply too low
C. organic loading rate too high
D. nutrient imbalance.
E. All the above can cause bulking. - ANS-E. All the above can cause bulking.
Industrial waste materials which are usually not compatible with municipal treatment
plants include:
A. chemical oxygen demand
B. Heavy metals.
C. petroleum fats , oils and greases
D. nitrogen and phosphorus compounds.
E. B and C - ANS-B. Heavy metals.
Sludge is observed to accumulate in the final clarifier. This may be caused by :
A. plugged sludge collectors return pumps or waste pumps
B. too high a return rate.
C. excessive solids wasting.
D. hydraulically overloaded clarifier
E. All of the above. - ANS-A. plugged sludge collectors return pumps or waste pumps
What is the relationship between the F/M ratio and the MCRT sludge age for a particular
plant when the aerator detention time is a constant value.
, A. these to control parameters are unrelated.
B. When one increases the other increases.
C. When one increases the other decreases.
D. it is a direct relationship
E. The F/M ratio is one tenth of the MCRT (Sludge Age) - ANS-C. When one increases
the other decreases.
Using results only from the settle-ability test and MLSS test of activated sludge solids
the operator will be able to
A. calculate the F/M ratio
B. Set the doge for chlorinating the return activated sludge
C. Calculate the MCRT
D. Calculate the SVI
E. A and C - ANS-D. Calculate the SVI
Which of the following F/M ratios would be in the proper rage for a contact stabilization
activated sludge plant?
A. 0.08
B. 0.12
C. 0.30
D. 0.75
E. 1.25 - ANS-C. 0.30
Short circuiting in a final sedimentation process:
A. is probably caused by mechanical failures.
B. usually represents a hydraulic deficiency of design or operation
C. Increases efficiency by facilitating rapid movement of treatment plant effluent
D. has no effect on plant performance.
E. All of the above. - ANS-B. usually represents a hydraulic deficiency of design or
operation
An old, over oxidized sludge at an underloaded plant produces mixed liquor solids that
A. settle slowly but produce a clear effluent
B. Settle rapidly leaving a turbid supernatant.
C. Cannot nitrify but turn septic readily in the final clarifier
D. All the above
The Activated Sludge Process:
A. requires preaeration
B. requires Activated Carbon
C. is an aerobic biological process.
D. Usually precedes primary sedimentation.
E. Requires 50% by volume old sludge to work effectively. - ANS-C. Is an Aerobic
biological process
A complete mix activated sludge plant has a fast settling sludge and high amounts of
pin floc leaving the clarifier. One way to correct this problem is to :
A. Increase the RAS Flow
B. Reduce Wasting Rates
C. Increase dissolved oxygen levels.
D. Increase the F/M ratio by wasting more
E. Increase the sludge age by wasting less. - ANS-D. Increase the F/M Ratio by
Wasting More
Which of the following flow rates should be measured if the operator is to control plant
properly?
A. Aeration rate or resulting dissolved oxygen level.
B. Influent or effluent.
C. return sludge
D. waste sludge
E. all the above - ANS-E. all the above
During start up your aeration tank produces excessive amounts of billowing white foam.
This can be corrected by:
A. Doing nothing, it will go away in a few hours
B. Increasing the sludge wasting rate
C. Seeding the process with sufficient good quality sludge
D. Spraying water on the foam until it is gone
E. Taking a weeks vacation - ANS-C. Seeding the process with sufficient good quality
sludge
,In solving an operational problem at a treatment plant:
A. there is almost always a good technical solution. It may require considerable
experience and time to learn whaat it is.
B. Human errors have to be corrected since the operator is at fault.
C. don't let the laboratory personnel influence you're judgement as to what the best
solution is.
D. standard textbooks in sanitary engineering are the best source of information.
E. It is best to do nothing until the TNRCCC sends a violation notice. - ANS-A. there is
almost always a good technical solution. It may require considerable experience and
time to learn whaat it is.
When the return sludge rate is too low, what happens?
A. the aeration tank will not fill
B. There will be insufficient organisms to treat the wast load entering the aeration basin
C. the activated sludge in the aerator will starve.
D. the sludge blanket in the secondary clarifier could become too high.
E. B and D - ANS-E. B and D
What factors affect how well the mixed liquor suspended solids settle in the final
clarifier?
A. flow velocity and or turbulence
B. temperature
C. quality of the mixed liquor solids
D. Short circuiting
E. All of the above - ANS-E. All of the above
The Active sludge process parameters which n operator can change directly are:
A. aeration rates.
B. waste rates.
C. the ratio of free swimming to stalked ciliates.
D. Return sludge rates.
E. All the above except C. - ANS-E. All the above except C.
Which of the following would you use to increase the degree of nitrification in an
activated sludge plant?
,A. increase the wast rates
B. increase dissolved oxygen levels and increase the sludge age
C. Remove excess alkalinity from the wastewater
D. Maintain a thicker sludge blanket n the clarifier
E. Inhibit the growth of the nitrifying bacteria with chemicals. - ANS-B. increase
dissolved oxygen levels and increase the sludge age
The Maximum change in the sludge wasting rates to maintain uniform operating
conditions should be about
A. 10- 20 % per day
B. 20-40 % per day
C. 40-60 % per day
D. 60-80 % per day
E. 100% per day - ANS-A. 10- 20 % per day
When operating an activated sludge plant, Which TSS concentration is most important
for process control?
A. Primary effluent
B. Aeration tank mixed liquor.
C. Return Sludge
D. Digester.
E. Plant influent - ANS-B. Aeration tank mixed liquor.
How many aeration tanks does a contact stabilization plant have?
A. one, like all the others
B. Four: contact, mix, reaeration and stabilization
C. Two if you count the digester as an aeration tank
D. a contact tank and a reaeration tank
E. none of this makes any sense to me. - ANS-D. a contact tank and a reaeration tank
Reducing the return sludge flow rate for an activated sludge system which has a good
settling sludge will.
A. Decrease the hydraulic detention time in the aeration basin
B. Increase the solids concentration in the aeration basin
C. cause the return sludge concentration to decrease
,D. have no effect on process performance.
E. increase the RAS concentration ad the clarifier blanket thickness. - ANS-E. increase
the RAS concentration ad the clarifier blanket thickness.
What items would you check if an activated sludge plant becomes upset?
A. Influent temperature.
B. Monthly average flow rates
C. BOD loadings MLSS sludge settle-ability D.O. and oxygen uptake rate
D. digester operation. E. Chlorinator settings. - ANS-C. BOD loadings MLSS sludge
settle-ability D.O. and oxygen uptake rate
Causes of sludge bulking include:
A. Low DO and presence of sulfides
B. Air supply too low
C. organic loading rate too high
D. nutrient imbalance.
E. All the above can cause bulking. - ANS-E. All the above can cause bulking.
Industrial waste materials which are usually not compatible with municipal treatment
plants include:
A. chemical oxygen demand
B. Heavy metals.
C. petroleum fats , oils and greases
D. nitrogen and phosphorus compounds.
E. B and C - ANS-B. Heavy metals.
Sludge is observed to accumulate in the final clarifier. This may be caused by :
A. plugged sludge collectors return pumps or waste pumps
B. too high a return rate.
C. excessive solids wasting.
D. hydraulically overloaded clarifier
E. All of the above. - ANS-A. plugged sludge collectors return pumps or waste pumps
What is the relationship between the F/M ratio and the MCRT sludge age for a particular
plant when the aerator detention time is a constant value.
, A. these to control parameters are unrelated.
B. When one increases the other increases.
C. When one increases the other decreases.
D. it is a direct relationship
E. The F/M ratio is one tenth of the MCRT (Sludge Age) - ANS-C. When one increases
the other decreases.
Using results only from the settle-ability test and MLSS test of activated sludge solids
the operator will be able to
A. calculate the F/M ratio
B. Set the doge for chlorinating the return activated sludge
C. Calculate the MCRT
D. Calculate the SVI
E. A and C - ANS-D. Calculate the SVI
Which of the following F/M ratios would be in the proper rage for a contact stabilization
activated sludge plant?
A. 0.08
B. 0.12
C. 0.30
D. 0.75
E. 1.25 - ANS-C. 0.30
Short circuiting in a final sedimentation process:
A. is probably caused by mechanical failures.
B. usually represents a hydraulic deficiency of design or operation
C. Increases efficiency by facilitating rapid movement of treatment plant effluent
D. has no effect on plant performance.
E. All of the above. - ANS-B. usually represents a hydraulic deficiency of design or
operation
An old, over oxidized sludge at an underloaded plant produces mixed liquor solids that
A. settle slowly but produce a clear effluent
B. Settle rapidly leaving a turbid supernatant.
C. Cannot nitrify but turn septic readily in the final clarifier
D. All the above
