Energy generated from renewable sources such as biogas, solar or wind is called green energy. Green energy is a term used to describe sources of energy that are considered to be environmentally friendly and non-polluting. These sources of energy may provide a remedy to the systematic effects of global warming and certain forms of pollution.

Biogas utilization can occur in waste water treatment plants, solid waste digestion plants and solid waste landfills, where the biogas can be collected and used.

When biogas is produced by means of an anaerobic process, the biogas consists of methane (CH₄) and carbon-dioxide (CO₂) along with some trace gasses such as water vapor, hydrogen sulphide (H₂S), nitrogen (N₂), hydrogen (H2) and oxygen (O₂).

The concentration of hydrogen sulphide in biogas can vary from 250 ppmv up to several volume percentages; it has an offensive odour of “rotten eggs” at concentrations as low as 50 ppbv and is toxic at concentrations above 100 ppmv.

At some applications H2S must be removed before the biogas can be given for utilization, for reasons of health, safety, environment and due to the fact that hydrogen sulphide gas is corrosive and can damage equipment like gas engines, boilers, piping, etc.

Desulphurization of the biogas is also required when biogas is upgraded to natural gas quality for injection into the gas grid.