It is disclosed a process to transfer a ligno-cellulosic feedstock from a low pressure zone to a high pressure zone. A slurry the ligno-cellulosic feedstock is first provided, which is then subjected to a multi-step liquid removal process comprising draining by gravity at least a portion of the free liquid; removing a first portion of the capillary liquid in a low pressure zone by continuously compressing a stream of the ligno-cellulosic feedstock to reach a moisture content in a first target range; removing a second portion of the capillary liquid by shearing and compressing the ligno-cellulosic stream in a plug forming device, to form a ligno-cellulosic feedstock plug having a moisture content in a second target range at an outlet of the plug forming device connected to the high pressure zone. In the removal of the first portion of the capillary liquid, at least one first compression device continuously compresses the stream of the drained ligno-cellulosic feedstock to a first control pressure, while conveying the stream of the drained ligno-cellulosic feedstock in a flow direction of a belt filter press.