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D.V.ANT

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Nitrite increases in secondary clarifiers
Mar 07^th, 2013, 2:02pm

We have about 0.3 mg/l nitrite in the supernate of our settled MLSS. After the clarifiers the nitrite level jumps to 4mg/l. There is a very long detention time in the clarifiers, 18 hours. Chlorine use is through the roof.

This time of year we get M.parvicella and use Pax-14 (aluminum salt) for comtrol. This is a MLE plant and we have been cold for 3+ months. Ammonia is controled by our permit

Anyone know why we should have more nitrite after the secondarys.

Mark

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sludgejudgeH

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Re: Nitrite increases in secondary clarifiers
Reply #1 - Mar 7^th, 2013, 9:27pm

18 hours is a very long retention time in the clarifier. A theory could be that ammonia is being released in the clarifier (this occurs under septic conditions) and then there is not enough oxygen available for full nitrification, hence nitrite build up.

M. Parvicella has three main causes, oil and grease, longer sludge age, and septicity. Septicity in the clarifier may very well be a big factor here.

Feel free to contact me offline via personal message if you'd like any assistance.

best regards,

Ryan

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Re: Nitrite increases in secondary clarifiers
Reply #2 - Mar 8^th, 2013, 7:19am

regarding the last post it's possible that ammonia not released but present to begin with as well.

I was somewhat involved with a plant that had some of the same problems with excessive retention time in the final clarifiers due to operating significantly under the plant's design hydraulic loading. They ended up operating the plant more like an SBR and didn't use the final clarifier but instead settled everything out in the aeration tank and decanted to the effluent. This may or may not be something to consider based on the plant's design. I know this worked well for them though.

I can't remember if they wasted from the aeration tank or if they ran the final clarifier more as a sludge thickener for wasting.

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D.V.ANT YaBB Newbies Offline I love Water and Wastewater.com Posts: 39 Company or Organization: City of Pendleton, OR	Re: Nitrite increases in secondary clarifiers Reply #3 - Mar 8^th, 2013, 10:39am Ryan, Thanks for the reply. It has given me some ideas. Mark
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david jenkins YaBB Newbies Offline I love Water and Wastewater.com Posts: 37 Company or Organization: david jenkins and associates	Re: Nitrite increases in secondary clarifiers Reply #4 - Mar 8^th, 2013, 12:01pm It is possible that the nitrite is coming from denitrification in the secondary clarifier sludge blanket. M. parvicella can denitrify but cannot take the nitrate all the way to nitrogen gas so it ends up producing nitrite
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NorCal_Wastewater1

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Re: Nitrite increases in secondary clarifiers
Reply #5 - Mar 9^th, 2013, 3:19pm

Certainly it sounds as if your clarifier is in a de-nite condition. This is probably the cause of the M. parvicella presence. THe sludge blanket sounds as if it is going septic on you. Can you reduce the retention time by 4-6 hrs? You might want to waste the first dose of increased waste sludge vs. running it through the RAS pumps just dump it to the WAS pumps to ensure you don't loop the MP back the aeration basin causign a disrupt there.

Dallas

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Have a great day,

Dallas

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D.V.ANT

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Re: Nitrite increases in secondary clarifiers
Reply #6 - Mar 15^th, 2013, 1:04pm

I increased the RAS. Increased the PAX-14 to combat the MP. The blanket in the clarifiers is 6" in one and 4" in the other, about 3000lbs solids between both clarifiers.

What we have noticed is the plant comes around over the weekend when we don't run the Screw Press. The old plant had much the same problem when we decanted the anaerobic digesters.

Please tell me if I am full of it but I am thinking the MP could be making it through the aerobic zone with stored food and denitrifying in the clarifier. So adding air to the swing cell would give the MP more time to eat in the basin and less food to denitrify with in the clarifier.

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sludgejudgeH

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Re: Nitrite increases in secondary clarifiers
Reply #7 - Mar 15^th, 2013, 8:04pm

I think it could be either partial denitrification by Microthrix or perhaps release of ammonia and partial nitrification. Each is a possibility. The main thing that will help is keeping the clarifier aerobic (easier said than done, especially with the long retention time there). Increasing the RAS rate and increasing the DO at the back end prior to the clarifier both may help as this limits the amount of oxygen used and also adds more oxygen to the clarifier before it's septic.

This may or may not be possible: but recycling some of the effluent back around to the clarifier may also help keep things aerobic by limiting the retention time there too.

Hydrogen Peroxide has been added to the centerwell of the clarifiers in some cases because it will break down to 1/2 part oxygen per part peroxide. This of course is a last resort and should only be done by someone with experienced hands.

You could test the nitrate in and out of the clarifier to determine if it is indeed partial denitrification by Microthrix. The control strategies for Microthrix Parvicella are reducing the sludge age, reducing septicity, and reducing oil and grease entering the plant.

If this nitrite increase happens when the screw press is running a possibility could simply be more food available (perhaps some food left on the plate at the end of the process from high BODs with the return stream) or on the other end perhaps some ammonia left on the plate and thus partial nitrification in the clarifier....

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