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boffin

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Hydrogen Sulphide Gas and Anaerobic Conditions.
Aug 21^st, 2012, 9:22pm

Hi All,

I’m looking for opinions/ help us settle a bet.

I have a long pressurised sewer pipe 11km (7 miles) and it is building up high levels of H2S gas (think 200ppm+). The dissolved oxygen at the start is 4mg/L and is about 2.5mg/L at the outlet.

I disagree with my co-workers on this issue. The text books and both of us agree that H2S should only build up in anaerobic conditions. I believe H2S will still be created when dissolved oxygen levels are low but present. I think it is normal for H2S to be created at 2mg/L. While my mate says anything above 0.5mg/L is the absolute cut-off of anaerobic bacteria.

Does anyone have a ‘magic’ target that would stop the H2S being created.

thanks,

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The sludge judge

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Re: Hydrogen Sulphide Gas and Anaerobic Conditions.
Reply #1 - Aug 21^st, 2012, 9:34pm

You need anaerobic conditions for sulfide formation. This occurs below an ORP of around -150. (DO meters become inaccurate under 0.5 mg/L)

How much of the sulfide is being oxidized in the pipe? Perhaps it's already present to begin with. If you are seeing the sulfide increase in the pipe it should be chlorinated to kill any growth present inside the pipe. It's possible to get a positive DO reading, but inside of any flocculated bacteria there's anaerobic conditions.

hope this helps/ not sure who wins though

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sobisch God Member Offline Posts: 1777 Gender: Company or Organization: L.U.M. GmbH	Re: Hydrogen Sulphide Gas and Anaerobic Conditions. Reply #2 - Aug 22^nd, 2012, 12:55am to add, you likely have some deposits, with anaerobic conditions. Kind regards T. Sobisch
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Domenic Paone

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Re: Hydrogen Sulphide Gas and Anaerobic Conditions.
Reply #3 - Aug 22^nd, 2012, 12:17pm

Inside a sewer pipe and for that matter in other environments, there can be biofilms formed on the surfaces which can do two things. One thay can limit the diffusion of oxygen into the biofilm and also contain enough microbes to consume the oxygen and alter the redox. Anaerobic bacteria can then thrive in that microenvirment with little to no oxygen. Nitrates have been used to control sulfide odors

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The sludge judge

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Re: Hydrogen Sulphide Gas and Anaerobic Conditions.
Reply #4 - Aug 22^nd, 2012, 1:32pm

I'd chlorinate to remove any biofilm present, keep in mind the chlorine will tie up the sulfide first. (you'll need to find the right dose, probably on the higher side.) This is the best option. If it fails, hydrogen peroxide is a good choice here because you'll attack the bacteria and also add oxygen. Nitrates will work, but not address the root cause if it's due to bacterial build up in the pipe.

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burwell000 YaBB Newbies Offline I love Water and Wastewater.com Posts: 2 Company or Organization: secret	Re: Hydrogen Sulphide Gas and Anaerobic Conditions. Reply #5 - Aug 22^nd, 2012, 7:48pm Thank's for the info, but did the chlorine is not bad in our body?
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boffin

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Re: Hydrogen Sulphide Gas and Anaerobic Conditions.
Reply #6 - Aug 23^rd, 2012, 1:02am

Thanks all,

Looks like you’re all agreeing on this one. I’m not keen on chlorine dosing the pipe as the outlet is right beside the front door of a busy Supermarket and I can’t afford the odour complaints.

I guess it might be best to stick to what I know and go back to using Ferrox to mask the odour.

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DoctorBug Senior Member Offline Water and Wastewater.com is the best! Posts: 498 Company or Organization: Michael Richard Wastewater Mic	Re: Hydrogen Sulphide Gas and Anaerobic Conditions. Reply #7 - Aug 25^th, 2012, 12:05am boffin: This is a common problem in long sewer lines. It is caused by either, or both, a biofilm or deposits that are anaerobic. The best solution that I have found (tried them all) is nitrate addition. Hope that this helps.
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