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A Beak

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Identifying Foam/Scum
May 30^th, 2012, 10:13am

Hello. I am hoping that someone out there can help me. Our aeration tanks have developed a viscous dark foam in the corners and around the edges in the last few weeks. I have seen it happen before, usually going into summer. It doesn't seem to cause us any real problems but i would still like to know more about it incase it becomes more of a problem.
We have two stages of secondary treatment, first a trickling filter that our O&M manual calls a "roughing filter" followed by two paralel aeration tanks. We have the option to either send the RAS straight to the AB's or mix it with the influent/TF recirc and send it over the biotower (tricklling filter). Currently it is being pumped to the AB's. Because all the influent is run through the biotower before making it to the AB's, soluable BOD levels are low.
Our current sludge age is around 10 days. I have thought about lowering the mlss to see if it would help, but i don't want to make any changes until i can identify the source.
Thanks!

Alex

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A Beak Junior Member Offline I love Water and Wastewater.com Posts: 80 Company or Organization: City of Biddeford WWTP	Re: Identifying Foam/Scum Reply #1 - May 30^th, 2012, 10:35am Also i should add that our SVI has dropped from an already low 70-80 to 40-50. Not sure if that is related. Again, any point in the right direction is greatly appreciated.
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The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: Identifying Foam/Scum Reply #2 - May 30^th, 2012, 12:21pm check your pm's. The foam may likely be either from denitrification or filamentous (M. Parvicella or Nocardia). That should be determined first. Typically a decrease in the SVI is due to a lower F/M and a increase in the WAS rate may be warranted. regards, Ryan
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A Beak

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Re: Identifying Foam/Scum
Reply #3 - May 30^th, 2012, 12:31pm

Thanks! I am not sure what your first sentence means. Pm's? I do not believe it is from denitrification because our DO runs consistantly over 2.0 and i have seen no decrease in nitrates leaving the tank. I checked the foam for filiments and i saw nothing. I just did a wet slide though. Would i be able to see more through staining? I think you are right about the low f/m. I calculate it daily and we land some where around 0.1. But thats using the plant influent BOD. Actual BOD to the AB after the tower is much lower.

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The sludge judge

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Re: Identifying Foam/Scum
Reply #4 - May 30^th, 2012, 12:38pm

If it's Microthrix Parvicella or Nodardia (cause: oil and grease) they're easily identified with the gram stain. When you stain the foam make sure to dilute it down at least 10:1 because the foam will be too concentrated otherwise to see anything.

Typically an SRT <7 days for nocardia and <10 days for Microthrix Parvicella to waste them out. Controlling oil and grease at the source (easier said than done) is the permanent solution. If it's a denitrification foam you'll notice the floc size in the foam is 2-3 times larger than in the MLSS.

by pm's I meant personal messages. (not PMS Grin

)

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A Beak

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Posts: 80

Company or Organization: City of Biddeford WWTP

Re: Identifying Foam/Scum
Reply #5 - May 30^th, 2012, 1:57pm

I have never seen a severe filamentous accumulation in person but i have seen pictures. Would i be able to see if there was a problem without staining? I have checked the scum multiple times under the micoscope and seen almost a total lack of filaments.
Does BOD loading come into play at all when it comes to "old" sludge? If the bacterial mass is underloaded would i see signs of old sludge (dark gelatinous foam) even if the SA is not that long?

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The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: Identifying Foam/Scum Reply #6 - May 30^th, 2012, 7:34pm it could be "dead bug" foam, you'd need to send it to a professional to know for sure.
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