McDonald Group International, Inc

Water, Wastewater, Environmental Engineering 

 

Problem Diagnosis Checklist - Activated Sludge Domestic Wastewater Processes


OBSERVATION:

 White, thick, billowing or sudsy foam on the aeration tank surface. (Too much food, not enough microorganisms.)

What Could be Wrong
This indicates not enough solids in the plant. Biologically active solids are needed to break down the "food" or waste strength coming in.

How to fix it

Build up more solids by reducing the amount of solids being wasted.


OBSERVATION:

Shiney, dark tan foam on the aeration tank surface. (Not.enough food for the microorganisms.)

What Could be Wrong

This may indicate that there are too many solids in the plant for the amount of waste material coming in.

How to Solve it

Try wasting more sludge from the process


OBSERVATION:

 Dark brown, almost blackish sudsy foam on the aeration tank surface.

What Could be Wrong

There is probably not enough DO in the plant and anaerobic conditions are being found.

How to Fix it

Check DO in the plant. If low, make sure enough air is getting to the plant. Make sure diffusers are all working. Make sure blowers are operating long enough. Check flows and raw BOD. A high influent BOD can cause low plant DO when even when hydraulically a plant is not overloaded. You may need to have the blowers resized and started.


OBSERVATION:

Localized clouds of homogenous sludge solids rising in certain areas of the clarifier. Mixed liquor settles fairly well with a clear supernatant.

What Could be Wrong

This may be an indication that denitrification is ocurring in the final settling tank. Take a sample of the sludge in the clarifier, stir it, and see if bubbles are released. If so, then maybe denitrification is occurring.

 How to Fix it

Try cycling your aeration system on and off during the day so that denitrification can be induced in the aeration tank as opposed to the settling tank. Also try increasing RAS. It could also be the sludge return system is not working well and needs repair.


OBSERVATION:

Clouds of billowing homogenous sludge rising and extending throughout the clarifier. Mixed liquor settles slowly, supernatant not very clear.

What Could be Wrong

There could be low DO in the aeration tank or the pH may be low in the aeration tank. Nutrient loading may be low (rare in domestic wastewater plants, but possible).

How to Fix it

Increase the DO in the plant. Test the liquid in the aeration tank. If less than 6.7, add either lime or caustic soda to bring the pH up. Low DO also causes the likelihood of the growth of filamentous organisms. Check under a microscope. If they exist, try chlorinating the return sludge line.


OBSERVATION:

Small particles of ashlike material floating on the clarifier surface.

 What could be wrong

This could either be the beginning of denitrification or more likely the sludge in the aeration tank has been in there too long. There may also be grease in the influent.

 How to fix it

Try increasing the amount of sludge wasted. Check for excessive grease in the influent and reduce it.  

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