Process for treating lignocellulosic biomass

A process for treating lignocellulosic biomass, successively comprising:

• a) pretreating a first acidic or neutral pH biomass in a pretreatment reactor to produce an acidic or neutral pretreated must (AM),
• alternating with
• a′) pretreating a second biomass in the pretreatment reactor to produce a basic pretreated must (BM), wherein
• (i) the second biomass is an acidic or neutral biomass, and sufficient aqueous solution (EB) is introduced into the pretreatment reactor to produce the basic pretreated must (BM), or
• (ii) the second biomass is a basic biomass, and basic aqueous solution (EB) is optionally introduced into the pretreatment reactor, and
• b) enzymatic hydrolysis in a hydrolysis reactor of a mixture of the acidic or neutral pretreated must (AM) obtained from b) a) with the basic pretreated must (BM) obtained from a′).