Basic Information about Substrates

Substrate ingredients
The organic substrate ingredients can be divided into carbohydrates, fats and proteins.
The substrate composition affects both the development of biological communities in the process and the resulting products of metabolism.
The composition of the main products of metabolism after the complete anaerobic degradation (CH₄, CO₂) are strongly affected by the composition of the fed substrate. Fats provide the highest specific amount of gas; proteins, with respect to the gas composition, the highest methane content in the digester gas.

Gas yield
The total amount of gas (gas yield) which is obtained during the retention time should be indicated as the amount of gas per 1 kg oDM (organic dry matter) fed, as this ensures that the different water contents are considered. Both nutrient composition and degree of degradation have a major influence on the gas yield.

Degradation degree
The degradation degree indicates what percentage of volatile solids were degraded during the retention time. Only when the substrate does not contain lignin, which can hardly be degraded by the methane bacteria , theoretically, a complete degradation is possible. In this case, the digested substrate will only contain the mineral components at the end of the process.

Retention time
The retention times has a large influence over the degradation rate and over the gas power and yield.