Secondary Process & Troubleshooting

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?

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

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

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?

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?

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

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?

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?

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?

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:

F/M ratio can be BEST described as:

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

A reduction of alkalinity across the secondary treatment process likely indicates

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?

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?

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?

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?

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?

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:

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

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 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?

A common problem with trickling filter operation is:

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

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:

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?

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