In this method, biogas is passed through the tower filled with special filling material. Unlike chemical desulphurization systems, biogas does not come into contact with any chemicals in biological desulphurization systems. Hydrogen sulfide removal is provided by a special bacterial species formed in the tower and clinging to the filled surfaces. Bacteria break down hydrogen sulfide and need oxygen for this. For this reason, special nutritional supplements used to feed oxygen and bacteria are made in the tower in a controlled manner.
Biological desulphurization systems are high-cost desulphurization systems as initial investment costs. However, it is more advantageous than chemical desulphurization systems in terms of operating costs. The biggest disadvantage of biological desulphurization systems is that the oxygen supplied into the tower reduces the calorific value of biogas. The high hydrogen sulfide ratio in the biogas can also cause blockages in the fillings inside the tower. The waste from this system is used for enrichment of the digester output manure.