Ozone pretreatment of humid wheat straw for biofuel production

In an attempt to maximize the amount of ozone reacting with lignin inside humid wheat straw, some of the ozone‐reactive lignin degradation products were washed away before a second ozonolysis delignification stage. The total contact time for the two stages was kept the same as that for a one‐stage process for comparison. A significant decrease in the Acid Insoluble Lignin ( AIL ) content of the straw resulted: from 13.04 wt. % (after a 30‐min one‐stage ozonolysis) to 9.34 wt. % (after a 30‐min two‐stage ozonolysis, separated by a washing step). This significant improvement was accompanied by an increase in released fermentable sugars from an enzymatic hydrolysis. The yield increased from 60% theoretical sugars to 80%. A further improvement in AIL (down to 7.36 wt. %) and released sugars (up to 90% theoretical) occurred when the moisture content (MC) of the straw entering the second stage was adjusted to the optimum value of the straw entering first stage (45 wt. %, predicted from an experimental design). The authors believe this is the first time results are published for the introduction of a two‐stage process separated by a washing step.