Anaerobic digester foaming

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Anaerobic digester foaming

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shawn

Posted 3/14/2008 9:08:41 PM

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We have anaerobic digesters with floating covers in our biological nitrogen removal (BNR) WWTP. Our digesters foam. We are using PAX-14 to control microthrix in the winter season of the semi-BNR mode. This has translated to less foam in the digesters, but there is still lots of foam. The PAX has kept the foam under control so that is isn't running out onto the building's roof or submerging the cover in foam. I am curious what other plants are using for foam control.

Post #8646

d jenkins

Posted 3/15/2008 12:34:06 PM

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What your message suggests is that the PAX-14 addition is sufficient to control the M.parvicella foaming in the activated sludge but not in the digester. This may be occurring becuase the solids concentration (and therefore the M.parvicella concentration) in the digester is much higher than in the mixed liquor. In this situation the better approaches to control would be:

(1) Reduce sludge age to below the washout value for M.parvicella (typically about 10 d). You will ahve to determine whether this is possible for the specific circumstances in your plant, while still meeting your efluent criteria.

(2) Install a surface wasting device(s) in the activated sludge system. This will selectively waste the M.parvicella-rich foam from the system and thereafter prevent M.parvicella from ever gaining a hold in the future.

Call or write if you wish to discuss further.

Post #8648

mjwboofer

Posted 3/18/2008 2:40:06 PM

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Foaming in an anaerobic digester can arise for a lot of reasons. Filamentous bacteria are only one possible contributor so it makes sense to me that you don't see 100% elimination in your foaming when you control for those organisms. I would recommend WE&T's article called "When it bubbles over" in the Oct 2006 issue, written by Massert et. al. for a good discussion of the causes of foaming in digesters. Unstable or overloaded digester conditions, excessive mixing (are you using a pump mix or gas mix?), and other factors contribute. Focusing on only one aspect will only get you partial results, as you've seen.

Good Luck!

Post #8669

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