I concur with Thomas Getz ...

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.