Optimizing Sulfite Pretreatment for Saccharification of Wheat Straw Using Orthogonal Design

An orthogonal designed experiment was used to investigate the effects of sulfite pretreatment on the components separation and saccharification of wheat straw. The process involved sulfite pretreatment of wheat straw under acidic conditions followed by mechanical size reduction using a high consistency refiner. Reaction temperature, retention time, and charges of sodium bisulfite and sulphuric acid were considered as key factors. The results showed the four factors had impact on saccharification of wheat straw. Raising the temperature, increasing the charge of sodium bisulfite or sulphuric acid, or extending the retention time would improve the dissolution of pentosan, lignin, and saccharification efficiency, while causing further conversion of pentose. The separation of lignin and pentosan from wheat straw was the main cause of improvements in saccharification. With an enzyme loading of 5 FPU cellulase plus 4 CBU β-glucosidase per gram of o.d. substrate, a glucose yield 72.45% was achieved using the substrate pretreated under the conditions of temperature 180 oC, sodium bisulfite charge 3%, sulfuric acid charge 1.48%, and retention time 20 min.