Foaming in STP

What color is the foam? Depending on the color may identify what type of foam it is and some more defining characteristics.

For example: A White foam will indicate a young sludge. Which means reduce your wasting to buildup your sludge age or MLSS (Mixed Liquor Suspended Solids).

Brown foam could indicate Nocardia (a filamentous organism) and or MLSS concentrations are high because of insufficient sludge wasting.

Dark or Black foam occurs when aeration is insufficient (anaerobic conditions) from industrial wastes. Which you may want to investigate industrial discharges for dyes or inks.

There are some mircoorganisms that are freezied dried on the market to help with biological activity that can be added to the aeration tanks to increase good biological activity.

You have to make your "BUGS" happy.

Foaming in a biological waste treatment plant is normally caused by filamentous bacteria. This could be due to such factors as sludge that is too old, insufficient DO content or poor nutrient balance.

You'll need to carry out a jar test to determine your optimum sludge age. Once this has been determined, increase sludge wastage until you achieve it.

Your DO content needs to be at least 5ppm for effective aerobic digestion. Test the DO content of the water. Increase aeration until you meet or exceed this level.

The optimum nutrient content of the water should be carbon: nitrogen: phosphorus = 100: 15 : 1. Adjust accordingly.

Carry out various test until you determine the cause of the outbreak of filamentous bacteria then apply the appropriate corrective measure as listed above. You may need to clean out and disinfect your aeration tank and introduce fresh sludge.

Both Bet Green and Dvader are correct and deserve a GA from me. Spot on guys!

Treat the causes, not the symptoms...

Q for the OP: Have you even looked at the sludge under a good microscope? If so, what do you see in your sample?

Also, I highly recommend that you obtain the following wastewater unit processes textbook:

Unit Operations and Processes in Environmental Engineering / Edition 2 by Tom D. Reynolds, Paul Richards

I consider this THE BIBLE of WW treatment unit processes design and O&M. I've been using it ever since I took my initial WW treatment design course when I was an UnderGrad Student back in the early 80's....have used it many a time!

All the answers are great here, wish I had your help when I was operating one! My only comment is since this is a hospital, I expect a lot of laundry is being done.

I would check the laundry to see if someone is putting too much detergent in the wash. Also, the chlorine from the laundry will kill your 'bugs'.

I always kept a separate tank of sludge bubbling away to add live 'bugs' to the aerator tank whenever I suspected I'd been bleached.

Fresh 'bugs' can be purchased in powder form, too.