Question of the Day: Hydrogen Sulfite Formation

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Question of the Day: Hydrogen Sulfite Formation
How is hydrogen sulfide formation controlled in wastewater treatment?

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8 Answers

  1. inconsistent nomenclature of the moiety of concern.  Are you talking about sulfite (really?) or sulfide (far more likely in a nasty environment, bad water, or next door to sulfide containing gas emissions.

  2. Aerobic digestion or anaerobic digestion?   Big difference 

  3. Hydrogen sulfide is caused by SRBs ... this is sulfate reducing bacteria.  These bacteria thrive in anaerobic environments.  They do not start out this way, but instead start out as SOBs, sulfate oxidizing bacteria which thrive in aerobic and anoxic environments.  They go through a metabolic change when there is no oxygen or nitrogen left, they make the change to anaerobic to survive.  Oxidation offers some of the most effective ways to control H2S.  Ozone, Oxygen  or Hydrogen Perioxide are very effective in controlling SRBs.  By killing the bacteria, you reduce the corrosion in the system being caused by part of the SRB metabolic process.    Calcium Nitrate can be used as well, feeding the SOBs to keep them from going to the SRB state.  Irons salts  and Lyming are other potential solution but can add solids to you system. 

  4. H2S is only controlled in certain areas of the plant, and will be higher in other areas.

    It is controlled by a system with good, constant flow, not in upset, plenty of aeration in the aerobic digester areas, and by steadfast prayers and concerns of the operators.

    H2S is responsible for most of the corrosion in a WWTP where exposed copper wiring (not sealed in silicone rubber) can corrode away in only a few days.

    This gas is very treacherous, because if you cannot smell it (after perhaps you did smell it), you are in extreme danger of unconsciousness and death.

  5. I have noticed the phenomena in Gas Fields where  H2s is vented in the atmosphere after Gas Purification. When the wind blows towards the Gas Purification Plants. The atmospheric H2S affects the cooling tower water where its Ph is reduced and water goes towards the acidic zone. 

    Solution: H2So4 dosing is stopped to control Ph of CT.

     

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    1. H2S levels must be astronomical to cause such a problem in the cooling tower, and really, the important thing to do is oxidize it out of the system.

  6. Depending on whether you are talking about an aerobic plant or anaerobic plant, the answers are different.  With an aerobic plant, the objective is to keep it aerobic because the bacteria, which produce the sulphide smells do not like oxygen.  There are two things which help, fully mixing plant using air to prevent dead areas where anaerobic bacteria grow and use fine bubble aeration to diffuse the air into the water and drive off carbon dioxide.  The latter produces better growth.  It must be remembered that there are other parts of a plant where sulphide odours are generated.  These are the sludge handling and wasting and any balance tanks especially if the liquor from sludge wasting is returned to the tank.  Whereas ferric chloride may be added in some plants, in others it is self defeating because bacteria with ferric chloride release sulphide after mixing.

    In the case of anaerobic digestion, sulphides will always be produced at some level, but if the methane produced and is burnt then the waste sulphide will oxidise, but this by itself causes problems because condensed water combines and generates sulphur acids, which are corrosive.  

  7. With effective wastewater treatment there should be no H2S formation. Usually the H2S is formed in long residence time sewers and as Sharon has stated it is extremely dangerous to staff working in treatment plants and pump stations (https://www.atsdr.cdc.gov/mmg/mmg.asp?id=385&tid=67). My introduction to this in the very beginning of my career in wastewater treatment was to watch from outside as a pump station worker enter a dry well only to collapse from H2S poisoning. By the time we got the breathing apparatus on and recovered him (about 2-3 minutes) he was dead. The local authority spent a lot of time, effort and money installing Oxygen injection/disolution systems on large flow sewers and chemical dosing (H2O2 and Ferric Chloride FeCl3) on smaller flow rate sewers in order to eliminate this problem.

  8. H2S can be a very dangerous compound - it can cause corrosion very rapidly in sewer networks, it causes odor in very small concentrations, and can even be deadly at high levels. The best way to control it is to prevent the development of H2S, either with oxygen injection upstream in the sewer lines, or with chemical dosing which can be very effective, but costly over the long term.  Does your question refer more to collection networks or the treatment plant?

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