Secondary Process & Troubleshooting Practice Questions Flashcards
- 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. What is the MOST
probable cause?
Young sludge
- PROBLEM:
Excessive white, billowing foam in the aeration tank surface.
What is the MOST probable cause?
MLSS too low
- What happens in the stabilization (re-aeration) tank in the contact-stabilization process?
Absorption and digestion of the waste material collected by microorganisms
- 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?
Reduce clarifier hydraulic loading rates
- 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. What is the
NECESSARY CHECK to confirm the cause?
Calculate the sludge age
- 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
MLSS F/M Ratio MCRT
Decreases Increases Decreases
- 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?
Increased organic load into tank
8
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?
Filamentous bacteria are causing the slow settling
- 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?
increasing the RAS decreased the detention time in the clarifier
- 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:
High flows are entering the treatment plant
- F/M Ratio can be BEST be described as:
The pounds of CBOD applied to a pound of MLVSS
- PROBLEM:
Small particles of ash-like (pinpoint floc) material floating on the clarifier surface.
Denitrification is NOT the problem. What is the BEST solution?
If MLSS grease exceeds 15% by weight, repair or replace scum baffles and
implement industrial waste ordinance.
- A reduction of alkalinity across the secondary treatment process likely indicates
Nitrification is occurring
- 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?
Under-oxidized and Young
- 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?
Anaerobic conditions are occurring in the aeration tank
- 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?
MLVSS, mg/L
- 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?
Increase the air SCFM to maintain proper DO
- The trickling filter plant is experiencing large amounts of filter flies and some offensive odors coming from the filters. Influent BOD and TSS are normal, and the weather is not a concern. What is the BEST METHOD to correct the problem?
Increase the recirculation flow rate
- 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
High OUR
- There are small particles of ash-like material floating on the clarifier surface. The MOST likely cause is:
Denitrification is occurring in the clarifier
- 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?
A shock load of formaldehyde has entered the plant
- 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?
Start and enforce sewer-use ordinances
- A common problem with trickling filter operation is:
Excessive sloughing of biofilm causing ponding
- A reason to switch to contact-stabilization mode of treatment would be:
To protect microorganisms from short-term toxic shock loads
- 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:
Pin floc
- 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?
When straggler floc is present in clarifier and settleometer
- The terms under-oxidized and over-oxidized are used to describe what parameter?
Sludge age or MCRT
