NOVELTY - Conditioning wood derived sulfur dioxide (SO2)-ethanol-water (SEW) spent liquor for fermentation with Clostridium, involves (a) exposing wood material to SEW cooking to obtain pulp, (b) squeezing the pulp and recovering SEW spent liquor, (c) washing the pulp to obtain MSEW spent liquor, where spent liquor is designated as MSEW, (d) evaporating the spent liquor and separating the precipitate to obtain evaporated liquor, (e) steam stripping the evaporated liquor, (f) liming the stripped liquor, and (g) exposing the limed liquor to obtain conditioned liquor.    USE - The method is useful for conditioning wood derived SEW for fermentation with Clostridium, preferably C.acetobutylicum (claimed). The wood material e.g. mixed forest biomass is useful for producing chemicals and biofuels.    DETAILED DESCRIPTION - Method (M1) for conditioning wood derived sulfur dioxide (SO2)-ethanol-water (SEW) spent liquor for fermentation with Clostridium, involves (a) exposing wood material to SEW cooking to obtain pulp, where the cooking is performed at 150 degrees C for 30 minutes, concentration of SO2 is 12 (weight/weight%), and ratio of liquor to wood is 3:1, (b) squeezing the pulp and recovering SEW spent liquor, (c) washing the pulp twice with 40% ethanol and/or water at 60 degrees C, and thrice with deionized water at room temperature, and adding the washings to the SEW spent liquor to obtain MSEW spent liquor, where spent liquor is designated as MSEW, (d) evaporating the MSEW spent liquor and separating the precipitate to obtain evaporated liquor, (e) steam stripping the evaporated liquor to obtain steam stripped liquor, (f) liming the steam stripped liquor at pH 8.9 to obtain limed liquor and precipitate SO2 in the form of calcium lignosulfonate, and (g) exposing the limed liquor to catalytic oxidation to obtain conditioned liquor, where the catalytic oxidation is carried out by ferrous sulphate heptahydrate (FeSO4.7H2O). An INDEPENDENT CLAIM is included for method (M2) for producing butanol from wood material, which involves fermenting the conditioned liquor obtained in method (M1) with Clostridium.