Dean Lampman
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Wastewater Public Utilities Quiz on Secondary Process & Troubleshooting, created by Dean Lampman on 10/03/2019.

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Secondary Process & Troubleshooting

Secondary Process & Troubleshooting

Question 1 of 27

1

PROBLEM:
Classic sludge bulking is occurring in the final clarifier of a conventional activated sludge plant. Indicators include: solids pouring over the weirs, excessive floc observed at the surface, and a homogenous (uniform) sludge blanket appearing throughout the clarifier. Sludge in settling test settles slowly leaving a cloudy supernatant with stragglers. What is the MOST probable cause?

Select one of the following:

  • Over-oxidized sludge

  • Hydraulic washout

  • Young sludge

  • SVI too low

Explanation

Question 2 of 27

1

PROBLEM:
Excessive white, billowing foam in the aeration tank surface.
What is the MOST probable cause?

Select one of the following:

  • pH too high

  • MLSS too low

  • Waste temperature too high

  • WAS too low

Explanation

Question 3 of 27

1

What happens in the stabilization (re-aeration) tank in the contact-stabilization process?

Select one of the following:

  • Adsorption of the activated floc

  • Adsorption of waste material by microorganisms

  • Agglomeration of the activated floc

  • Absorption and digestion of the waste material collected by microorganisms

Explanation

Question 4 of 27

1

PROBLEM:
Good settling in the 30-minute settleability test. Excessive floc billowing in the clarifier and washing out. Sludge scrapers and RAS system appear normal. What is the BEST solution to fix the problem?

Select one of the following:

  • Lower aeration tank effluent weirs

  • Increase RAS

  • Add chlorine to RAS

  • Reduce clarifier hydraulic loading rates

Explanation

Question 5 of 27

1

PROBLEM:
Classic sludge bulking is occurring in the final clarifier of a conventional activated sludge plant. Indicators include: solids pouring over the weirs, excessive floc observed at the surface, and a homogenous (uniform) sludge blanket appearing throughout the clarifier. Sludge in settling test settles slowly leaving a cloudy supernatant with stragglers. What is the NECESSARY CHECK to confirm the cause?

Select one of the following:

  • Weir over flow rate

  • Determine effluent suspended solids concentration

  • Calculate the sludge age

  • DO in aeration tank

Explanation

Question 6 of 27

1

In a well operated activated sludge plant, when the RAS flow rate is decreased but the WAS flow rate remains constant, the expected conditions would be

Select one of the following:

  • MLSS Conc. F/M Ratio MCRT
    decreases increases decreases

  • MLSS Conc. F/M Ratio MCRT
    decreases decreases increases

  • MLSS Conc. F/M Ratio MCRT
    increases increases decreases

  • MLSS Conc. F/M Ratio MCRT
    increases decreases increases

Explanation

Question 7 of 27

1

In an activated sludge plant, if the DO in the aeration tank suddenly decreases and the aerators are not the problem, what is the MOST PROBABLE cause?

Select one of the following:

  • F/M ratio decreased

  • Increased organic load into tank

  • Denitrification occurring

  • MCRT too long

Explanation

Question 8 of 27

1

PROBLEM:
Upon arriving at the package treatment plant serving a small community, you find a uniform sludge blanket rising throughout the clarifier. A settleability test reveals a very slow-settling sludge leaving a very clear supernatant. MLSS test results are normal, but a calculation of the SVI shows a high sludge volume index. What is the MOST likely cause of the high sludge blanket?

Select one of the following:

  • The operator has wasted too much sludge, causing a young sludge condition

  • An extreme rain event washed out the majority of the solids

  • Filamentous bacteria are causing the slow settling

  • An overdose of chlorine has killed the floc forming and filament bacteria

Explanation

Question 9 of 27

1

PROBLEM:
Solids are washing out of the secondary clarifier of the activated sludge plant. Plant personnel increase the return activated sludge (RAS) flow rate, which slows the problem temporarily, but then it worsens after 30 minutes. What is the cause of the plant problem?

Select one of the following:

  • increasing the RAS increased the detention time in the clarifier

  • increasing the RAS decreased the detention time in the clarifier

  • increasing the RAS increased the detention time in the aeration tank

  • iIncreasing the RAS caused the DO in the aeration tank to increase

Explanation

Question 10 of 27

1

PROBLEM:
Solids are washing out of the secondary clarifier of the activated sludge plant. A settleability test shows good settling CAN occur. The MOST likely cause of the problem is:

Select one of the following:

  • High flows are entering the treatment plant

  • The RAS rate is too low

  • The sludge collector mechanism is rotating counter-clockwise

  • Denitrification is occurring in the chlorine contact tank

Explanation

Question 11 of 27

1

F/M ratio can be BEST described as:

Select one of the following:

  • The pounds of CBOD applied to a pound of MLVSS

  • The amount of influent TSS applied to the aeration tank

  • The loading of solids to a trickling filter

  • The amount of soluble CBOD fed to an RBC

Explanation

Question 12 of 27

1

PROBLEM:
Small particles of ash-like (pinpoint floc) material floating on the clarifier surface. Denitrification is NOT the problem. What is the BEST solution?

Select one of the following:

  • If MLSS grease exceeds 15% by weight, repair or replace scum baffles and implement industrial waste ordinance.

  • Increase depth of sludge blanket

  • Increase DO

  • Install pretreatment holding basin and/or adjust influent pumps for rate of influent flow.

Explanation

Question 13 of 27

1

A reduction of alkalinity across the secondary treatment process likely indicates

Select one of the following:

  • Anaerobic conditions

  • Anoxic conditions

  • Nitrification is occurring

  • Denitrification is occurring

Explanation

Question 14 of 27

1

A microscopic exam shows a predominance of amoebae, flagellates with a few free swimming ciliates. The floc appears large and irregularly shaped and not very dense. What is the condition of the MLSS?

Select one of the following:

  • Over-oxidized

  • Under-oxidized

  • Young

  • Under-oxidized and Young

Explanation

Question 15 of 27

1

Dark brown, almost gray/black sudsy foam on the aeration tank surface. Mixed liquor color is very dark brown, to almost black. There is the detection of a septic or sour odor in the area of the aeration tank. What is the MOST likely cause?

Select one of the following:

  • Aerobic conditions are occurring in the aeration tank

  • Septic conditions have occurred in the clarifiers

  • Anaerobic conditions are occurring in the aeration tank

  • Anoxic conditions are occurring in the pre-denitrification zone

Explanation

Question 16 of 27

1

Localized clouds of fluffy homogenous (uniform) sludge rising in certain areas of the clarifier. Mixed liquor settles slowly, and leaves stragglers in the supernatant of the settleometer. What is the NECESSARY CHECK to confirm the cause?

Select one of the following:

  • Influent VSS, mg/L

  • Influent TSS, mg/L

  • Effluent CBOD, mg/L

  • MLVSS, mg/L

Explanation

Question 17 of 27

1

Dark brown, almost gray/black sudsy foam on the aeration tank surface. Mixed liquor color is very dark brown, to almost black. There is the detection of a septic or sour odor in the area of the aeration tank. What is the BEST method to correct the problem?

Select one of the following:

  • Decrease the RAS rate to decrease the clarifier detention time

  • Increase the WAS rate to wash the septic sludge from the system

  • Increase the air SCFM to maintain proper DO

  • Decrease the air SCFM to conserve energy

Explanation

Question 18 of 27

1

The trickling filter plant is experiencing large amounts of filter flies and some offensive odors coming from the filters. Influent CBOD and TSS are normal, and the weather is not a concern. What is the BEST METHOD to correct the problem?

Select one of the following:

  • Increase the distributor arm speed

  • Increase the recirculation flow rate

  • Decrease the recirculation flow rate

  • Decrease the filter media sloughing potential

Explanation

Question 19 of 27

1

The effluent of the activated sludge plant is high in CBOD and ammonia. A microscopic exam shows a high amount of organism activity. If an oxygen uptake rate (OUR) test is run on the aeration tank effluent, the expected test result would be:

Select one of the following:

  • A low OUR

  • No OUR

  • High OUR

  • The OUR test is inconclusive

Explanation

Question 20 of 27

1

There are small particles of ash-like material floating on the clarifier surface. The MOST likely cause is:

Select one of the following:

  • Nitrification is occurring in the clarifier

  • Denitrification is occurring in the clarifier

  • Denitrification is occurring in the collection system

  • Grease content of the MLSS is below detectable limits

Explanation

Question 21 of 27

1

The aeration tank DO has been running normal (1.5 to 2.0 mg/L) the whole month. Todays DO reading has spiked to nearly 6.0 mg/L in the aeration tank, and the clarifier and plant effluent are cloudy. What is the MOST likely cause of the rise in DO?

Select one of the following:

  • The aeration blowers were left on overnight

  • A shock load of high organic strength waste has entered the plant

  • A shock load of rain water has entered the plant

  • A shock load of formaldehyde has entered the plant

Explanation

Question 22 of 27

1

The aeration tank DO has been running normal (1.5 to 2.0 mg/L) the whole month. Todays DO reading has spiked to nearly 6.0 mg/L in the aeration tank, and the clarifier and plant effluent are cloudy. This problem has occurred often in the past, and causes the plant to be out of compliance several times per year. What is the BEST METHOD to correct this problem?

Select one of the following:

  • Run a higher MLSS to maintain more nitrifiers in the aeration tank

  • Reseed the plant with fresh RAS from another plant after each occurrence

  • Start and enforce sewer-use ordinances

  • Increase DO and WAS rates

Explanation

Question 23 of 27

1

A common problem with trickling filter operation is:

Select one of the following:

  • Excessive sloughing of biofilm causing ponding

  • Poor primary clarifier TSS removal

  • Media breakdown, causing ponding

  • Excessive air flow through the media causing aerobic conditions

Explanation

Question 24 of 27

1

A reason to switch to contact-stabilization mode of treatment would be:

Select one of the following:

  • To combat long-term toxic loads entering plant

  • To protect microorganisms from short-term toxic shock loads

  • To improve slowly metabolized CBOD removal

  • To increase overall treatment efficiency

Explanation

Question 25 of 27

1

The aeration tank is approaching under-loaded conditions (high MLSS) because of old sludge in the system. The expected conditions seen in the final clarifiers would be:

Select one of the following:

  • Straggler floc

  • Pin floc

  • Fluffy, slow-settling sludge

  • Slow-settling sludge leaving a very clear supernatant

Explanation

Question 26 of 27

1

A common remedy for activated sludge system problems is to increase the waste activated sludge (WAS) flow rate. When would an increase of WAS rate NOT be correct?

Select one of the following:

  • When pin-point floc is observed on the clarifier surface

  • When thick, scummy foam is seen on the aeration tank surface

  • When the aeration system is critically under-loaded

  • When straggler floc is present in clarifier and settleometer

Explanation

Question 27 of 27

1

The terms under-oxidized and over-oxidized are used to describe what parameter?

Select one of the following:

  • Sludge age or MCRT

  • OUR

  • Microorganism count

  • RAS rates

Explanation

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