Biogas plants are important for the local agricultural sector. They process livestock waste and liquid manure in a fermentation process to yield fertilizer. The over-fertilization of farmland can thus be avoided and precious groundwater resources protected. In contrast to other biogas companies, biwi purifies the water derived from the fermented liquid manure by means of a unique reverse-osmosis system; the resultant water is so pure that it can be safely discharged into a nearby stream. The resultant concentrate represents a valuable liquid fertilizer suitable for agricultural use. The solids derived from the fermented residues are used to produce certified organic fertilizer pellets (biwi bio-pellets). Another fraction is used to make liquid fertilizer (Wicon Concentrate).
The biogas derived from the fermentation of the raw materials is then sent to the “upgrading” plant. In the first stage of this facility, the biogas is purified of contaminating particles and undesirable gases (e.g., sulfur compounds). In further processing stages, the pressure of the biogas is increased so that it can be separated into its chief components – methane (CH4) and carbon dioxide (CO2) – in a 3-stage process using special membranes.
The methane thus obtained is then purified in a further process until a purity of more than 99% CH4 is achieved. The bio-methane is then liquified. Using a 3-stage compressor, the bio-methane is brought down to a temperature of -163 °C. The gas is thus converted into LNG (Liquefied Natural Gas) which requires only one six-hundredth the storage volume. This bio LNG is stored in special cryogenic storage tanks for later use in heavy truck transportation.
The CO2 obtained from the “upgrading” process must likewise be purified so that it meets the requirements of the foods industry. To do this, a special analytical unit guarantees that the gas purity is under constant supervision. Using a compressor, the CO2 is brought down to a temperature of -30 °C and thus liquefied, facilitating transport.