WEF Discussion Forums
Operation and Maintenance
excessive dark foam on aeration tanks
I'm posting this for an adjacent township plant, they have no computer at their site. The problem started with a waste pump that failed and they didn't waste for several days as sludge built up over 16 feet in their clarifier. They mentioned their plant data and effluent quality hasn't changed. I asked them to check for filamentous, they did find a lot and proceeded to chlorinate the RAS until they seemed to get rid of them. It's been a couple months now I think and they still have over 12 inches of dark foam floating on the aeration tanks. I mentioned to check the sludge age or calculate the SRT and perhaps implement SRT control. Does anyone have any idea of what can cause the foam problems? The township really has not much for industry or restaurants. They've checked their pumpstations and find no problems at any of the stations with foam either.
Dark frothy type foams are filamentous for sure, the fact that the wasting was discontinued for quite some time confirms that fact. The best way to eliminate it is to continue wasting until the frothy foam is gone this means lowering the Aeration S.S. (M.C.R.T.)very low, what would help also is if they are capable of spraying with chlorination solution on the Aeration Tanks to break it up and help settle it so it can be wasted out of the Plant(very important). If chlorinating the return did not seem to work then this is my only suggestion. Chlorinating the return works for certain types of filamentious others require spraying the actual surface with chlorine solution to break it up to aid in settling it and wasting it out of the Plant.
Yes, I just had a former MOE specialist (scientist) send over some interesting stuff about the 3 types of filamentous that cause foaming. Nocardia seems to be the most common for dark old foam indicating excess SRT or sludge age. Chlorinated spray was listed as part of the solution, thanks very much. They are working on some further analysis, sludge judge sus. solids so as to calculate srt's and figure out how many kg's of sludge they have (SDR ratio) compared to aeration solids kg's etc. I suspect they're carrying perhaps too many solids in the clarifier, not enough wasting. I appreciate your comments....thanks!
while i am new to the forum and your problem may be solved i would add a few additional thoughts
according to toni g an expert microbiologist the presence of nocardia foam is an indication of the condition of the MLSS and the operation practices of the facility. when you mentioned the sludge was stuck in the clarifier it leads to the conclusion that sludge quaality suffered and the response was the proliferation of the foam event.
chlorinated sprays can reduce the foam but based on toni's studies it doesn't address the basic factors - often foams come and go in AS especially with changes in temp and loadings
instead of chlorination it is perhaps more difficult but better operational control for the MLSS and operation to remove the foam
removing the foam will be wasting pounds from the process and gets the filament out of the environment where they are the top dog so to speak.
vac truck or foam trapping and removal may take more time but from other facilities trying to deal with the foam it has been more succesful
in any case hope they are doing well now that spring is on us.