The invention consists in a process and a device for the continuous liquefaction of biomass. An upward flow in the ambient liquid of the fermentor brings the biomass to the surface. Feeding of new biomass and removal of waste material can be performed at any time so that continuous fermentor operation permits constant biogas output. Compared with common farm-based digesters the reactor loading can be increased by at least factor two to three while yielding the same amount of gas.
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