Water and Wastewater.com Help Forums - sulfate reducing bacteria

Alana YaBB Newbies Offline I love Water and Wastewater.com Posts: 7 Company or Organization: CH2M	sulfate reducing bacteria May 30^th, 2012, 9:56am Help, I was asked : "If you have a certain amount of sulfate in water, how do you find what % do you convert to H2S (via sulfate reducing bacteria) before you can smell it" Don't I need the chemical eqn for sulfate reduction to H2s? Also I know the value for the olefactory threshold. Theer are many sulfate reducing bacteria.
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H2O_Tech

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Re: sulfate reducing bacteria
Reply #1 - May 30^th, 2012, 10:15am

If you know the olfactory threshold, then work backwords?

Other issue is, as you state, is the various typs of SO4 reducers. The various metabolic pathways to prime the pump for sulfate reduction hav edifferent thermodynamics, so there's no one-size fits all.

Is the goal to use SO4 levels as some sort of predictor of H2S production?

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Alana

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Re: sulfate reducing bacteria
Reply #2 - May 30^th, 2012, 10:27am

H2O_Tech,
Yes that is the goal. I have seen ranges for the olafactory thresholds ranging from 0.001 to 0.1 ppm, but a tighter range of 0.004 to 0.02 ppm may be better. We have 1116 ppm SO4- in our water (which is almost 3 X more than the client's standard) but yes, we also are worried about the rotten egg smell.

Do you know how i could start as a rule of thumb to solve this (know how much sulfate will be converted to smell H2S)?

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The sludge judge

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Re: sulfate reducing bacteria
Reply #3 - May 30^th, 2012, 12:12pm

As long as the process is kept aerobic and you have a positive ORP the sulfate shouldn't be getting reduced. We don't know much about your processs, but keeping everything aerobic at the source would be optimal.

It doesn't matter how much sulfate is present, if things are aerobic this reaction won't happen. If you do generate sulfide odor, hydrogen peroxide or ferric chloride will oxidize/ precipitate the sulfide. Also calcium nitrate can be used to keep the redox above where sulfate reduction will happen/ the bugs will use the oxygen molecule in the nitrate before they work on the sulfate.

best regards,

Ryan

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Alana

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Re: sulfate reducing bacteria
Reply #4 - May 30^th, 2012, 4:10pm

Yes, we have about 60 mg/L N-NO3. So the plan is to add methanol to reduce it to N2. This will be done at ORP 0 – (-50) mV and no oxygen. I was told that SO4-2 conversion to H2S will be negligible, and no odor will be detectable. I just wanted to put some numbers to it.

Basically, the water will have 60 ppm N-NO3 and 1180 ppm SO4-2 and a few hundred ppm methanol will be added to create anaerobic (anoxic) condition. This is just a borderline to start sulfate reduction and I was wondering

1. What if negligible, but still a small amount of sulfate is converted to H2S, is odor going to be detectable?
2. Is it possible to maintain zero sulfate reduction while achieving complete denitrification?

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The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: sulfate reducing bacteria Reply #5 - May 30^th, 2012, 7:26pm you'll have to experiment with what ORP works best for you. Normal wastewater contains around 300 ppm sulfate and as long as you don't get the redox too low I believe you'll be allright. Try to keep it as high as possible and still denitrify.
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sobisch God Member Offline Posts: 1777 Gender: Company or Organization: L.U.M. GmbH	Re: sulfate reducing bacteria Reply #6 - May 31^st, 2012, 1:27am Dear Alana, so it is not directly what you asked for. In addition to the previous comments you have to keep in mind #there will be no sulfate reduction as long as there is nitrate #any dissolved iron ions will bind sulfide. Kind regards T. Sobisch
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Alana YaBB Newbies Offline I love Water and Wastewater.com Posts: 7 Company or Organization: CH2M	Re: sulfate reducing bacteria Reply #7 - May 31^st, 2012, 3:21pm would the H2s be in the air or water?
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sobisch God Member Offline Posts: 1777 Gender: Company or Organization: L.U.M. GmbH	Re: sulfate reducing bacteria Reply #8 - Jun 1^st, 2012, 1:27am There is a partition between both phases. It needs a limiting concentration of dissolved H2S to be traceable in air.
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DS

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Re: sulfate reducing bacteria
Reply #9 - Jun 1^st, 2012, 5:36pm

Sobisch is right.

besides that, the partitioning also is pH dependent. H2S is a weak acid with a pKa around 7, so typically 50% of the sulfide will be in the undissociated form at neutrality, and this is the one that is volatile. The more acidic you go, the more the equilibrum will be driven to the volatilisation. the more basic the solution is, the less you will smell

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almar1965

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Re: sulfate reducing bacteria
Reply #10 - Jun 2^nd, 2012, 7:48am

Hi

Dirk raises a very good point about pH. Martin Marietta have a very lucrative business selling Mg(OH)2 to raise the pH in sewers.

There is an alogorythm used by nitrate companies to guage dosing which involves retention time, COD, pH and temperature. If you contact Richard Bennett of EnVent he can help you.

best regards
Alistair

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Alana YaBB Newbies Offline I love Water and Wastewater.com Posts: 7 Company or Organization: CH2M	Re: sulfate reducing bacteria Reply #11 - Jun 5^th, 2012, 12:52pm Thank you all for your information.
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