It involves special oxides and iron oxyhydroxides which are able to reduce the amount of hydrogen suphide H₂S contained within the anaerobic digesters in biogas plants.

Biogas is formed by the action of bacteria that transform organic matter waste into digestors in anaerobic conditions (lack of oxygen). Among the waste coming from human activity which needs to be managed we have: forestry residues, liquid manure from livestock farms, remains from agricultural production, from meat, fish and vegetable canning industry, as well as solid urban waste, mud coming from industrial and domestic wastewater purifying plants, remains from paper industry, and so on.

Biogas created in the anaerobic digesters cannot be used as such since it contains impurities that have to be removed or reduced to amounts that are not harmful for the subsequent energetic use in the form of heat or electricity.

Biogas is mainly made of methane, but it contains considerable amounts of CO₂ and modest ones of hydrogen sulphide. The objective is to remove the CO₂ and the H₂S to achieve biomethane which is pure enough for its energy use. ChromaFer DB 02 and DB 04 make it possible to considerably decrease the amount of H₂S in the anaerobic digestor itself. This will allow the purification adjustment through active carbon filters or other systems. If this early reduction in H₂S content does not take place, the final purification filters would saturate ahead of time or increase the processing cost.