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Maryam Wastewater YaBB Newbies Offline I love Water and Wastewater.com Posts: 15 Gender: Company or Organization: Waterworks	Coarse bubble diffusers for Anoxic Tanks Jun 21^st, 2012, 11:51am Hi All, Did anybody use coarse bubble diffusers in Anoxic tanks ? I am designing an anoxic tank and we can not use mixer.I am not sure how will be design of anoxic tank with coarse bubble diffusers and how much will be the risk of having oxygen in tanks. Regards Maryam
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Maryam Wastewater YaBB Newbies Offline I love Water and Wastewater.com Posts: 15 Gender: Company or Organization: Waterworks	Re: Coarse bubble diffusers for Anoxic Tanks Reply #1 - Jun 21^st, 2012, 12:05pm The pupose od Anoxic tank is denitrification for this plant
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Re: Coarse bubble diffusers for Anoxic Tanks
Reply #2 - Jun 21^st, 2012, 3:10pm

While I have no direct experience with coarse bubble mixing in anoxic treatment; I have read about its use on this Forum. My thought is that you must control DO at very low concentrations because denitrification ceases at very low concentrations of DO. My thought is that you might cycle the air to the coarse bubble discharge and install a very low DO shut down. My reasoning is that subjecting the influent to coarse bubble mixing is that there may be an oxygen demand from RAS and influent soluble BOD that would prevent aerobic conditions.

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DS God Member Offline sapere aude Posts: 1583 Company or Organization: Indept. Freelance Consultant	Re: Coarse bubble diffusers for Anoxic Tanks Reply #3 - Jun 22^nd, 2012, 2:12am Hi maryam, why can't you put in a mixer? how fast does the sludge settle in absence of mixing?
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Rakesh_Shah YaBB Newbies Offline Water and Wastewater.com is the best! Posts: 22 Ahmedabad Gender: Company or Organization: Anand Consultants	Re: Coarse bubble diffusers for Anoxic Tanks Reply #4 - Jun 22^nd, 2012, 7:45am Why not pump out from the tank and put the outlet of the pump back into the bottom of the tank at 2-3 places if required? Mixing will be achieved without Oxygen getting added into the tank.
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Maryam Wastewater

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Re: Coarse bubble diffusers for Anoxic Tanks
Reply #5 - Jun 22^nd, 2012, 11:07am

Hi ,

Thank you for your reply

The problem of mixer is tanks are steel with roof so I am not sure that mounting mixer from roof of the tank will be a good idea.

Roof need to be design for 200 psf snow load and I dont know it can carry any other weight or not

Maybe having a pumping system is better idea without risk of having oxygen in Anoxic tanks

Thanks
Maryam

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DS

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Re: Coarse bubble diffusers for Anoxic Tanks
Reply #6 - Jun 22^nd, 2012, 3:33pm

Hi Maryam,

you can use short & intermittent coarse bubble "aeration" to resuspend the sludge in the tank, but it should be short. The faster the sludge resettles, the more frequent you will have to do that. This mode can work but denitrification efficiency is less compared to a normal mixed tank, so this lower efficiency will have its price either in a higher effluent N or a longer denitrification phase.

best regards,
DS

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WasteH2ODave Ex Member	Re: Coarse bubble diffusers for Anoxic Tanks Reply #7 - Jul 10^th, 2012, 7:55am What about using compressed N2 or inert 'welding' gases for the mixing. You don't add oxygen, and you get mixing.
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Lindekugel YaBB Newbies Offline Good news, everybody! Posts: 2 Arizona Gender: Company or Organization: Arizona State University	Re: Coarse bubble diffusers for Anoxic Tanks Reply #8 - Jul 10^th, 2012, 5:22pm I was also going to suggest using something inert like Argon or possibly helium (since nitrogen and oxygen should be right out), but if you have a sealed dome, that may cause other issues. I think re-circulation pump is the way to go.
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Re: Coarse bubble diffusers for Anoxic Tanks
Reply #9 - Jul 10^th, 2012, 10:18pm

Mixing via pumps and jets would be one option. Floc shear may be a consideration in your case, and that may make pumps less suitable.

Mixing via a through wall horizontal unit or units may be anther option.

There are many possibilities. Established mixer manufacturers offer top-mount mixers designed specifically for covered tanks for industrial, chemical, nuclear, WWTP, and other uses. Don't limit yourself to common wastewater equipment manufacturers or you may find yourself with few options.

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C. Gillen God Member Offline Applied Environmental Biotechnology Posts: 773 Ireland Gender: Company or Organization: BioFuture Ltd.	Re: Coarse bubble diffusers for Anoxic Tanks Reply #10 - Jul 11^th, 2012, 9:12am Hi Maryam, I agree with DS that it can be done but it should be the last resort as it will have a negative effect on your denitrification. Best regards, Cgillen
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