Crystallization of elemental sulfur produced in the biotechnological desulfurization of gas was studied in laboratory and industrial reactors to enhance the settleability of the elemental sulfur. It was found that the elemental sulfur settles best when the elemental sulfur particles are agglomerated, which is enhanced by partial dissolution of the sulfur particles with sulfide to polysulfides under anoxic conditions and subsequent biological oxidation of these polysulfides back to elemental sulfur.