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?
Over-oxidized sludge
Hydraulic washout
Young sludge
SVI too low
PROBLEM: Excessive white, billowing foam in the aeration tank surface. What is the MOST probable cause?
pH too high
MLSS too low
Waste temperature too high
WAS too low
What happens in the stabilization (re-aeration) tank in the contact-stabilization process?
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
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?
Lower aeration tank effluent weirs
Increase RAS
Add chlorine to RAS
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 with stragglers. What is the NECESSARY CHECK to confirm the cause?
Weir over flow rate
Determine effluent suspended solids concentration
Calculate the sludge age
DO in aeration tank
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 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
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?
F/M ratio decreased
Increased organic load into tank
Denitrification occurring
MCRT too long
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?
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
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 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
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
The RAS rate is too low
The sludge collector mechanism is rotating counter-clockwise
Denitrification is occurring in the chlorine contact tank
F/M ratio can be BEST described as:
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
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.
Increase depth of sludge blanket
Increase DO
Install pretreatment holding basin and/or adjust influent pumps for rate of influent flow.
A reduction of alkalinity across the secondary treatment process likely indicates
Anaerobic conditions
Anoxic conditions
Nitrification is occurring
Denitrification 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?
Over-oxidized
Under-oxidized
Young
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?
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
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?
Influent VSS, mg/L
Influent TSS, mg/L
Effluent CBOD, mg/L
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?
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
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?
Increase the distributor arm speed
Increase the recirculation flow rate
Decrease the recirculation flow rate
Decrease the filter media sloughing potential
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:
A low OUR
No OUR
High OUR
The OUR test is inconclusive
There are small particles of ash-like material floating on the clarifier surface. The MOST likely cause is:
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
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?
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
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?
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
A common problem with trickling filter operation is:
Excessive sloughing of biofilm causing ponding
Poor primary clarifier TSS removal
Media breakdown, causing ponding
Excessive air flow through the media causing aerobic conditions
A reason to switch to contact-stabilization mode of treatment would be:
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
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:
Straggler floc
Pin floc
Fluffy, slow-settling sludge
Slow-settling sludge leaving a very clear supernatant
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 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
The terms under-oxidized and over-oxidized are used to describe what parameter?
Sludge age or MCRT
OUR
Microorganism count
RAS rates
