Improving the overall sugar recovery by mixing wheat straw and hybrid poplar biomass during steam explosion and enzymatic hydrolysis

The economic success of a potential biorefinery is directly related to the use of low cost biomass. Moreover, it is unlikely that a biorefinery would use only one type of raw material during bioconversion. While a more heterogeneous raw material is less expensive, the efficacy of the bioconversion process using mixed biomass has not been investigated. Considering, the seasonal availability of wheat straw and all year round availability of hybrid poplar in the Pacific Northwest, this study aims to determine the influence of mixing wheat straw and hybrid poplar biomass on the overall sugar production via steam pretreatment and enzymatic saccharification. Five different biomass samples, M1: 100% poplar, M2: 75% poplar, 25% wheat straw; M3: 50% poplar, 50% wheat straw; M4: 25% poplar, 75% wheat straw and M5: 100% wheat straw, were impregnated with 3% SO₂ and steam pretreated at 195˚C during 5 minutes. The composition of biomass samples did not influence the enzymatic digestibility of steam pretreated solids where a cellulose-glucose conversion in a range of 79 to 84% was obtained for all the substrates after 96 hours of saccharification. Surprisingly mixes M2-M4 exhibited on average 14% and 23% higher overall glucose and xylose recovery respectively, in comparison with 100% poplar. Finally, steam pretreatment is as robust method to process concurrently two different types of feedstocks such as wheat straw and hybrid poplar.