Other substances may be present in small amounts in the biogas. Nitrogen (N2) and oxygen (O2) may be present in concentrations up to a couple of percent (this would typically be the case if fresh air is added to the biogas for desulphurization), but these gasses are obviously not an environmental hazard. Hydrogen (H2) may also be present in small amounts, but will be eliminated during combustion. Two potentially hazardous gasses, carbon monoxide (CO) and ammonia (NH3) may also be present in trace amounts, but given a safe and controlled combustion process, CO is completely eliminated.
Deux gaz potentiellement dangereux, à savoir le monoxyde de carbone (CO) et l'ammoniaque (NH3) peuvent également être présents sous forme de traces, mais grâce à un processus de combustion sûr et contrôlé, le CO est éliminé dans sa totalité.