chemical precipitation using iron hydroxide.

For precision desulphurization, impregnated or doted activated carbon is normally used (catalytic oxidation and following adsorption).

Alternatively, chemisorption on iron oxide- or hydroxide-coated materials in an external column can be applied for precision desulphurization. Chemisorption using zinc oxide in external columns is basically also applicable, but currently not state-of-the-art for precision desulphurization of biogas.

The six most widespread technologies are

pressure swing adsorption,

water scrubber,

physical absorption (using organic solvents),

chemical absorption (using organic solvents),

high-pressure membrane separation and

cryogenic upgrading.