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Secondary Process & Troubleshooting
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Questions in this quiz (27)
1PROBLEM:
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?- AOver-oxidized sludge
- BHydraulic washout
- CYoung sludge
- DSVI too low
2PROBLEM:
Excessive white, billowing foam in the aeration tank surface.
What is the MOST probable cause?- ApH too high
- BMLSS too low
- CWaste temperature too high
- DWAS too low
3What happens in the stabilization (re-aeration) tank in the contact-stabilization process?
- AAdsorption of the activated floc
- BAdsorption of waste material by microorganisms
- CAgglomeration of the activated floc
- DAbsorption and digestion of the waste material collected by microorganisms
4PROBLEM:
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?- ALower aeration tank effluent weirs
- BIncrease RAS
- CAdd chlorine to RAS
- DReduce clarifier hydraulic loading rates
5PROBLEM:
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?- AWeir over flow rate
- BDetermine effluent suspended solids concentration
- CCalculate the sludge age
- DDO in aeration tank
6In 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
- AMLSS Conc. F/M Ratio MCRT
decreases increases decreases - BMLSS Conc. F/M Ratio MCRT
decreases decreases increases - CMLSS Conc. F/M Ratio MCRT
increases increases decreases - DMLSS Conc. F/M Ratio MCRT
increases decreases increases
- AMLSS Conc. F/M Ratio MCRT
7In 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?
- AF/M ratio decreased
- BIncreased organic load into tank
- CDenitrification occurring
- DMCRT too long
8PROBLEM:
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?- AThe operator has wasted too much sludge, causing a young sludge condition
- BAn extreme rain event washed out the majority of the solids
- CFilamentous bacteria are causing the slow settling
- DAn overdose of chlorine has killed the floc forming and filament bacteria
9PROBLEM:
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?- Aincreasing the RAS increased the detention time in the clarifier
- Bincreasing the RAS decreased the detention time in the clarifier
- Cincreasing the RAS increased the detention time in the aeration tank
- DiIncreasing the RAS caused the DO in the aeration tank to increase
10PROBLEM:
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:- AHigh flows are entering the treatment plant
- BThe RAS rate is too low
- CThe sludge collector mechanism is rotating counter-clockwise
- DDenitrification is occurring in the chlorine contact tank
11F/M ratio can be BEST described as:
- AThe pounds of CBOD applied to a pound of MLVSS
- BThe amount of influent TSS applied to the aeration tank
- CThe loading of solids to a trickling filter
- DThe amount of soluble CBOD fed to an RBC
12PROBLEM:
Small particles of ash-like (pinpoint floc) material floating on the clarifier surface. Denitrification is NOT the problem. What is the BEST solution?- AIf MLSS grease exceeds 15% by weight, repair or replace scum baffles and implement industrial waste ordinance.
- BIncrease depth of sludge blanket
- CIncrease DO
- DInstall pretreatment holding basin and/or adjust influent pumps for rate of influent flow.
13A reduction of alkalinity across the secondary treatment process likely indicates
- AAnaerobic conditions
- BAnoxic conditions
- CNitrification is occurring
- DDenitrification is occurring
14A 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?
- AOver-oxidized
- BUnder-oxidized
- CYoung
- DUnder-oxidized and Young
15Dark 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?
- AAerobic conditions are occurring in the aeration tank
- BSeptic conditions have occurred in the clarifiers
- CAnaerobic conditions are occurring in the aeration tank
- DAnoxic conditions are occurring in the pre-denitrification zone
16Localized 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?
- AInfluent VSS, mg/L
- BInfluent TSS, mg/L
- CEffluent CBOD, mg/L
- DMLVSS, mg/L
17Dark 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?
- ADecrease the RAS rate to decrease the clarifier detention time
- BIncrease the WAS rate to wash the septic sludge from the system
- CIncrease the air SCFM to maintain proper DO
- DDecrease the air SCFM to conserve energy
18The 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?
- AIncrease the distributor arm speed
- BIncrease the recirculation flow rate
- CDecrease the recirculation flow rate
- DDecrease the filter media sloughing potential
19The 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:
- AA low OUR
- BNo OUR
- CHigh OUR
- DThe OUR test is inconclusive
20There are small particles of ash-like material floating on the clarifier surface. The MOST likely cause is:
- ANitrification is occurring in the clarifier
- BDenitrification is occurring in the clarifier
- CDenitrification is occurring in the collection system
- DGrease content of the MLSS is below detectable limits
21The 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?
- AThe aeration blowers were left on overnight
- BA shock load of high organic strength waste has entered the plant
- CA shock load of rain water has entered the plant
- DA shock load of formaldehyde has entered the plant
22The 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?
- ARun a higher MLSS to maintain more nitrifiers in the aeration tank
- BReseed the plant with fresh RAS from another plant after each occurrence
- CStart and enforce sewer-use ordinances
- DIncrease DO and WAS rates
23A common problem with trickling filter operation is:
- AExcessive sloughing of biofilm causing ponding
- BPoor primary clarifier TSS removal
- CMedia breakdown, causing ponding
- DExcessive air flow through the media causing aerobic conditions
24A reason to switch to contact-stabilization mode of treatment would be:
- ATo combat long-term toxic loads entering plant
- BTo protect microorganisms from short-term toxic shock loads
- CTo improve slowly metabolized CBOD removal
- DTo increase overall treatment efficiency
25The 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:
- AStraggler floc
- BPin floc
- CFluffy, slow-settling sludge
- DSlow-settling sludge leaving a very clear supernatant
26A 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?
- AWhen pin-point floc is observed on the clarifier surface
- BWhen thick, scummy foam is seen on the aeration tank surface
- CWhen the aeration system is critically under-loaded
- DWhen straggler floc is present in clarifier and settleometer
27The terms under-oxidized and over-oxidized are used to describe what parameter?
- ASludge age or MCRT
- BOUR
- CMicroorganism count
- DRAS rates
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- Description
- Wastewater Public Utilities Quiz on Secondary Process & Troubleshooting, created by Dean Lampman on 10/03/2019.
- Author
- Dean Lampman
- Language
- English
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- History
- Created on 10 Mar 2019 · updated on 12 Mar 2019
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