This indicates not enough solids in the plant. Biologically active solids are needed to break down the "food" or waste strength coming in.
Build up more solids by reducing the amount of solids being wasted.
This may indicate that there are too many solids in the plant for the amount of waste material coming in.
Dark brown, almost blackish sudsy foam on the aeration tank surface.
There is probably not enough DO in the plant and anaerobic conditions are being found.
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.
Localized clouds of homogenous sludge solids rising in certain areas of the clarifier. Mixed liquor settles fairly well with a clear supernatant.
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.
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.
Clouds of billowing homogenous sludge rising and extending throughout the clarifier. Mixed liquor settles slowly, supernatant not very clear.
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).
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.
Small particles of ashlike material floating on the clarifier surface.
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.
Try increasing the amount of sludge wasted. Check for excessive grease in the influent and reduce it.