Biogas is a renewable fuel that can be used to power stationary engines that generate electricity and in some instances, co-generate heat. Sources of biogas include landfills, dairy and poultry farms, and wastewater treatment plants. Biogas consists primarily of methane and carbon dioxide and typically contains contaminants such as hydrogen sulfide and siloxanes. These contaminants can be detrimental to both the engine and the emission control catalyst and must be reduced to very low levels in upstream gas cleaning systems before the gas is burned in the engine. Johnson Matthey supplies advanced SCR systems equipped with oxidation catalyst to reduce NOx, CO, VOC and formaldehyde (CH2O) emissions and prevent air pollution from stationary engines at many different biogas sources. Some of these installations are described below: