Wet biomass in this category refers to organic wastes such as residual flows from the food and beverage industry, vegetable, fruit and garden wastes, or organic wet faction of household wastes. The residual flows are mentioned in the NTA8003 and published by the Netherlands Standardization Institute. For this category, a minimum biogas production of 25 Nm3 (natural gas equivalent) for tonne feedstock is requested. Manure is not included in this category.
The biomass is digested in a state-of the-art anaerobic digestion installation to produce biogas. The installation consists of storage and pre-treatment, digestion installations, combustion of biogas and post treatment and storage of digestate (i.e. dewatering, drying, in some cases hygenisation and storage). On average, the residence time of the organic waste in the fermenter is around 30 days and biogas is produced.
Biogas consists mainly of methane (in average 60%) and carbon dioxide (33-38%) in addition to contaminants such as sulphur, water vapor and oxygen. The biogas is desulfurized prior to it being fed into a gas motor to produce heat and electricity. The Activities Decree on emissions for combustion plants requires that the gas motors comply with the emission limits for SO2 and NOx.