Effect of Intermediate Washing on Ozonolysis Delignification and Enzymatic Hydrolysis of Wheat Straw

Wheat straw was pretreated with ozone to increase the enzymatic hydrolysis yield. Ozonolysis pretreatment was performed in two stages with an intermediate washing step with water in between. Part of the delignification products (lignin fragments) were removed by a washing step so ozone was used to oxidize more lignin rather than oxidizing lignin fragments. Three parameters, i.e. Initial Water Content (IWC) in wheat straw, Washing Starting Time (WST), and Washing Contact Time (WCT), were optimized to minimize Acid Insoluble Lignin (AIL) content of ozonated wheat straw. Performing an experiment using optimal parameters' values, i.e. IWC equal to 45 wt. %, WST equal to 20 minutes and WCT equal to 80 seconds, showed a drop in AIL content to 9.35 % with an increase in enzymatic hydrolysis yield to 80 % of the theoretical. Readjusting water content of wheat straw to 45 % before performing the 2nd ozonolysis stage further reduced AIL content to 7.36 % and increased the hydrolysis yield to 90 %. Increasing wheat straw fiber size from < 2 mm to < 6 mm decreased the hydrolysis yield to 72 %. All results were considered significant improvements when compared to untreated wheat straw with AIL content of 20.5 % and hydrolysis yield of 23 %.