The invention relates to a process for treating a feedstock (3) in a liquid form comprising the steps of providing a feedstock (3)； optionally diluting the feedstock (3) by addition of an aqueous solution (5) in order to obtain a feedstock slurry (11), and subjecting the feedstock slurry (11) to an anaerobic fermentation in a biogas reactor (13) thereby forming a liquid phase (15) and gas phase (17), wherein the biogas reactor (13) is supplied with feedstock (3) or feedstock slurry (11) at least in an amount via which content of ammonium of at least 2.7 g/l as determined according to DIN 38406-5 is set in the liquid phase (15) and in that the anaerobic fermentation is conducted at a pressure of at least 0.13 MPa of the gas phase (17) in the head space of the biogas reactor (13). The invention also relates to the plant to perform the process.
