The standard applies to gas from sludge digestion tanks. Oxygen is determined in connection with possible explosive mixtures with methane [explosion limits 5-14% (V/V) in air]. The determination of the carbon dioxide content is important for assessing the progress of the fermentation process and the calorific value of the gas. In general, the remainder consis s of approximately 90% methane. Other components that are present to a small extent are sometimes also determined.
NEN 6681-1981 history
1981NEN 6681-1981 Waste water - Volumetric determination of carbon dioxide and oxygen in gases