The subject of the invention is a process for treating lignocellulosic biomass comprising the following steps:



a) conditioning the lignocellulosic biomass,
b) washing said particles,
c) separating the aqueous solution from the washed biomass particles,
d) impregnating said lignocellulosic substrate with an acid liquor,
e) carrying out a solid/liquid separation of the impregnated lignocellulosic substrate,
f) pretreating said substrate from step e) by cooking,
g) carrying out an enzymatic hydrolysis of the pretreated lignocellulosic substrate,
h) carrying out a fermentation of the hydrolyzate from step g),

and introducing the used aqueous washing solution into a step of said biomass treatment process which is after the pretreatment step f), and/or into an enzyme production step and/or into a step of producing/propagating the microorganisms necessary for steps g) or h).