Hi

I am not an expert but I know gasses are usully seperated by freezing. since you need to reduce temperature by more than 100 degrees, I dont think it can be done without advanced equipment

I'm guessing that you are mainly interested in the hydrogen and want to remove all other gasses.  In anaerobic conditions, you don't need to worry about the oxygen because any that is generated will be immediately used up.  CO2 can be scrubbed out of the bubble stream by passing the gas through a solution of Potassium Hydroxide or Sodium Hydroxide.  For the DIYer, you can make this with Lye from the grocery store.  Nitrogen from denitrification may be a problem.  Also, is there a possibility of methane being produced?  Both nitrogen and methane will make it through the scrubber.

Thank you very much for this information, this is was really helpful for me!