Impact of Sodium meta bisulphite on biological treatment processes

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I would like to know if sodium meta bisulfite discharged in industrial effluent will have a negative impact on the biological activity of an anaerobic reactor or an activated sludge reactor treating the effluent.

If so, what precautions should be taken to negate the negative impact?

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9 Answers

  1. I concur with the group: the load is going to cost in terms or oxygen or oxidant and possibly iron salts. Is there an industrial pre-treatment program in place, to at least equalize flow, and a policy to allocate the increased operation and maintenance and fair portion of capital costs to the discharger?

  2. I concur with Thomas Getz with regards the anaerobic reaction with metabisulphite although it does depend on the level of bisulphite present.  

    I do have experience of bisulphite in aerobic systems and again it depends on the level of bisulphite in proportion to the volume of the system.  In the case of trickle filters or biotowers there can be problems with the presence of sulphite oxiidising to sulphate, and which causes anaerobic sulphate reducing bacterial growth underneath the deposits, which generates sulphide smells (varying from rotting cabbage, smelly feet to rotting eggs).  Higher levels of bisulphite may inhibit surface growth.

    In the case of activated sludge, using air, there is usually little problem because the bisulphite is oxidised to sulphate, and although there is a drop in pH this is corrected by the removal of carbon dioxide.  In the case of pure oxygen, it becomes a problem because the carbon dioxide is not driven off so the pH may run at 6.5 therefor the bisulphite will cause a further depression of the pH.  This will alter the microbial population dynamics.

    The problem occurs, in air activated sludge systems, when oxygen is lost temporarily, or there are areas of poor mixing/oxygen transfer.  Under these conditions the sulphate produced will allow the development of anaerobic sulphate reducing bacteria and again the odour problem.  

    The only other area of concern is the sludge itself.  Sludge will turn anaerobic on storage anyway.  The presence of sulphate will cause the mal-odours encountered with these growths.

  3. It is an oxygen scavenger, so while it won't have any adverse effect on anerobic bioreactors, it will definitely drive up oxygen consumption in aerobic systems such as activated sludge, MBR or MBBR

  5. Andre, the metabisulfite anion is unstable under anaerobic conditions and will be reduced to hydrogen sulfide. This will happen rather quickly - probably less than an hour.   There will be a corresponding reduction in methane formation, in proportion to the metabisulfite,  as the organic load is diverted to sulfur reduction,    Then hydrogen sulfide (H2S) will appear in the biogas and offgas streams.  This will also happen quickly.   The H2S will partition into the gas and liquid effluent at about 50/50 ratio depending on the pH of the anaerobic reactor.   To mitigate the impact of H2S you can add ferrous chloride or ferric chloride which will precipitate the H2S as ferrous sulfide (FeS.)  These iron salts are strong acids which may require additional alkalinity.   

    The aerobic process which receives the anaerobic effluent will experience a heavy non-carbonaceous oxygen demand as the sulfide is oxidized to sulfate.  And this  oxidation will release acidity so there may be a pH depression. 

    All of these effects are concentration-dependent.  There should not be any permanent toxicity to either anaerobic or the aerobic process.  

    Kind regards,  

  6. No direct experience here but this is what I would look out for….

     

     

    In anaerobic/anoxic stages of treatment, it may not be a problem (other reactions aside) as it’s a reducer.  However, then it may be concerning for any oxidative stages.

    I reread a paper on dechlorination (one of the common uses of sodium bisulphite) that says look out for decreased DO where 4 parts sulfite reacts with 1 part oxygen and lower PH.  

     

    If this is an anticipated effluent, not yet in your loading then I would say it’s worth it to start an ORP monitoring protocol through the various zones. This will give you a baseline of comparison when the chemical loading comes in.  A lot can be learnt from ORP readings through the various biological processes’.   See https://www.ysi.com/ysi-blog/water-blogged-blog/2013/08/orp-management-in-wastewater-as-an-indicator-of-process-efficiency

     

    I would assume there are no disinfecting properties left as its applied at effluent producers point as part of their process or treatment at discharge.  Would be interesting to find out why the industry is using it and see if there are alternatives or better accuracy of dosing if they are off setting an oxidant.   On the discharger side or your side an oxidant as mentioned by Ian could balance the reduction but with variable loading this would be a challenge.    I work with Electro Oxidation systems where I would use direct anodic oxidation technology linked to an ORP control to adjust current/reaction and achieve balance of the influent.

  7. Hi Andre, difficult with industrial waters as inflow characterisation should be known since influence of other elements likely

    is there no pretreatment, should be, again for industrial water?

    You can most likely pre treat with oxidising agent?

    regards

     

  9. Hello Andre, I do not have direct experience with this, but since sodium meta bisulphite is a strong reducing agent, it acts as a disinfectant and a oxygen scavenger, neither properties being helpful in an activated sludge process.  The disinfectant properties may also be detrimental to an anaerobic reactor where the microbes are more sensitive.  In terms of precautions - it depends on the concentration in the industrial effluent, but the aim would be to oxidise with an oxidant before treatment.  This may be a challenge as there are possibly a number of other constituents that will react to the applied oxidant, and in addition oxidising sodium meta bisulphite is likely to generate SO2 which is a pungent aesthetically unpleasant odour.  Oxidants you could consider are oxygen, chlorine, hydrogen peroxide.  Hope this helps

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