The process of crude sulfur removal can be undertaken either biologically or chemically.

Biological sulfur removal

Biological sulfur removal employs microorganisms that consume hydrogen sulfide. This process is only suitable for crude sulfur removal. The microorganisms can be placed directly into the fermenter.

Chemical sulfur removal

Chemical sulfur removal involves the use of compounds that bind with sulfur in the fermenter. Iron oxide is the best compound for this purpose.
Because some sulfur (specifically hydrogen sulfide)can  remain in the biogas after crude sulfur removal, some preparation paths may require an additional fine sulfur removal process before CO2 separation. The most suitable processes for fine sulfur removal are active carbon adsorption and zinc oxide adsorption.