The Biogas and air are mixed with packing media flowing in a counter current with circulating water in a vertical column. The packing media enlarge the contact surface area between the H2S in the gas flow, the nutrients in the water and the oxygen, also acting as a carrier for the bacteria. When limited quantities of oxygen are added to biogas, specific aerobic bacteria such as Acidothiobacillus oxidise H2S into elemental sulphur and/or sulphuric acid.
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