Fractionation of cellulase and fermentation inhibitors from steam pretreated mixed hardwood

► Steam pretreatment of hardwoods releases lignin-derived phenolic inhibitors. ► Washing of pretreated solids with water removes inhibitors (sugar oligomers, phenolics). ► Hot water (90 °C) recovers more hydrophobic and inhibitory phenolics than cold water (25 °C). ► Phenolic inhibitors act on both enzymes and fermentation microorganisms. ► Inhibition is decreased through fractionation of the inhibitors using XAD-7 or activated carbon.