Alkaline pretreatment is more effective on agricultural residues and herbaceous crops than on wood materials. This is also the case for the ammonia freeze explosion process . Wet oxidation pretreatment involves the treatment of the biomass with water and air, or oxygen, at temperatures above 120°C, sometimes with the addition of an alkali catalyst . This method is suited to materials with a low lignin content, since the yield has been shown to decrease with increased lignin content, and since a large fraction of the lignin is oxidised and solubilised. As with many other delignification methods, the lignin cannot be used as a fuel, which considerably reduces the income from by-products in large-scale production