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Prodigy Child

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Digester upset
May 08^th, 2012, 7:59am

I have a foaming digester. Running acid alk as we speak. ph is 7.2, 35c temp. Raw feed ph is 5.5, 250,000 gal digester wit secondary digester. Feeding 25gpm due to foaming normally 100 gpm. I did feed off the bottom of the sec digester to help bring in alkalinity and settle it down. As soon as raw feed back on it foamed. Looking for a product to bring ph in raw back into normal range. Any other thoughts here? Undecided

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The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: Digester upset Reply #1 - May 8^th, 2012, 10:23am Be sure you're not seeding your digester with WAS full of Nocardia or M. Parvicella, this may be a contributing (or main) cause. Please let us know the volatile acid/alkalinity ratio as soon as possible. Also, many times more mixing helps. best regards, Ryan
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Prodigy Child

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Re: Digester upset
Reply #2 - May 9^th, 2012, 8:43am

I found ALK to be low at 2000. Acid was 78. Raw feed was 5.5pH. We investigated today at the collection system. We found a wetwell at a pH of 5.3. Triggered more investigating as to why. Ordering some MAg Hyd to raise the pH to neutral. I do have some gas production today so not all is lost. Dropped feed to 1000gpd and will slowly increase feed in a few days. Hopefully it will cure and come back to full strength in a couple weeks. Getting to be the busy season at the end of the month.

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Geoff

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Re: Digester upset
Reply #3 - May 10^th, 2012, 12:37am

Looks like you caught it in time.

As a rule of thumb I used to aim for the following:

Alk > 1500 (preferably >2000)
VA < 100
pH > 7.0

A low feed pH will chew up the alkalinity very quickly. Backing off the load sure does help.

Find out who in your catchment is responsible for the low pH feed and dip them head first into in feed flow. Just a suggestion. Wink

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Prodigy Child

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Re: Digester upset
Reply #4 - May 10^th, 2012, 7:45am

I found the leg of the collection system that is responsable. Seems like it is an accidental/action of overdose of Bioxide. The crew operating that area needed to finish what we had of the product to make room for new product. It seems more is not better as far as it goes. I can spend some time adjusting pH as the system gets flushed out, feed off the second digester for added alkalinity to the Primary Digester. We should be back up to full force in a couple weeks I anticipate. Roll Eyes

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The sludge judge

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Re: Digester upset
Reply #5 - May 10^th, 2012, 8:45am

I'm glad things are improving. I don't believe an overdose of bioxide (nitrate) is to blame. An overdose would give you more problems with denitrification in the primary clarifier than anything else. Also remember that denitrification produces alkalinity so the addition of it to the collection system (where the bugs use it as an oxygen source) also creates alkalinity.

I would investigate upstream of the wet well where the low pH was and look for someone who is giving you low pH, very acidic wastewater.

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Prodigy Child

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Re: Digester upset
Reply #6 - May 10^th, 2012, 1:06pm

Rural area, there are only homes here. Nothing that has the potential to dose that hot of pH. Before the bioxide we are fine. After the bioxode we are not. There are not any homes in between the wetwells. Pumping station to station to overcome elevation before it runs gravity to the plant. Therefore it is at least a constituent to the problem. It had rained so with some I&I cam the push and greater volume of sludge, but it should have been diluted. If it was this hot coming in what was the pH initially! It also so happens that the ammonia pushed through the plant. A week before we had non detect ammonia. That one day we had 9 mg/l of ammonia at the effluent, then the day after it was back down to 2.3mg/l. Bioxide......had a part in it for sure.

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DoctorBug

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Re: Digester upset
Reply #7 - May 10^th, 2012, 5:56pm

Prodigy Child:

Bioxide (calcium nitrate) cannot account for this problem at any concentration. I have over-dosed this and the result is high nitrite in the plant and some denitrification.

Your description sounds like you got a flush by the rainfall of a very septic collection system. If this had a pH of 5.5, this indicates possible high fermentation to acetic acid (which has a pKa value of 5.5) in old sludge in this arm of your collection system. This old sludge may also had high ammonia so some broke through the plant. Also, septicity causes organic acids (like acetic acid) and hydrogen sulfide, both of which inhibit nitrifiers (these recover quickly as you found). High organic acids also can cause foaming of an anaerobic digester, due to causing over-growth of several anaerobic filaments that cause digester foaming. Been here, done this...

Hope that this helps.

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