The invention relates to a method for treating biomass (2). In a step (S10), biomass (2) and an impregnation liquid are fed into a first reactor unit (10) such that the biomass (2) is impregnated with the impregnation liquid while the biomass (2) is transferred through the first reactor unit (10) by a conveyor means (11). In another step (S20), the impregnated biomass (2a) is transferred from the first reactor unit (10) to a separation unit (25), wherein at least a part of the impregnation liquid is separated from the impregnated biomass (2a) within the separation unit. In a step (S30), the separated impregnation liquid is discharged from the separation unit (25), such that a first part (26a) of the impregnation liquid is recirculated back to the first reactor unit (10). The invention further relates to a system for treating biomass (2).