Fermentation process starting from cellulosic biomass and involving the recirculation of detoxified stillage into the process

A system for producing at least one target chemical derivable from cellulosic biomass, comprising;

• a) at least one cellulosic biomass pretreatment vessel for pretreating at least a part of provided cellulosic biomass to pretreated cellulosic biomass, connected to
• b) a hydrolysis vessel for hydrolysing at least a part of the pretreated cellulosic biomass to cellulosic hydrolysate, said cellulosic hydrolysate comprising fermentable sugars and inhibitory substances, further connected to
• c) a fermentation vessel comprising a fermentation biocatalyst for fermenting at least a part of the fermentable sugars, providing a fermented hydrolysate comprising the primary target chemical and inhibitory substances, further connected to
• d) a first separation means, for separating the primary target chemical from the fermented hydrolysate and for providing a spent hydrolysate, further connected to
• e) a detoxification vessel, comprising a detoxification biocatalyst selected from the group consisting of wild type, mutant and recombinant filamentous fungi, for detoxifying the spent hydrolysate from at least one inhibitory substance and for providing a detoxified spent hydrolysate, further connected to
• f) recirculation means for recirculating at least a part of the detoxified spent hydrolysate to at least one of the at least one pretreatment vessel of a), the hydrolysis vessel of b) and the fermentation vessel of c),
• wherein the hydrolysis vessel and the fermentation vessel may be the same vessel or two different vessels.