Biogas can be upgraded to biomethane, that can then be fed directly into the natural gas grid or used as a vehicle fuel to reduce greenhouse gas emissions by separating the carbon dioxide (CO₂)/methane (CH₄) mixture. There are different methods to separate the carbon dioxide (CO₂)/methane (CH₄) mixture in biogas. Water washing is one of the more popular methods of biogas separation. This is effective as carbon dioxide is soluble in water and methane is almost insoluble. The carbon dioxide is absorbed at high pressure in the water and desorbed from the water at lower pressure and in presence of an airflow. This air flow will also take up hydrogen sulphide (H₂S) present in the water which causes the typical rotten egg smell when released into the environment. Hydrogen Sulphide (H₂S) is therefore removed from the carbon dioxide (CO₂) enriched air using mobile and/or fixed filters with activated carbon prior to discharge to avoid complaints from workers and neighbours.