Evaluation of the effect of mixed agricultural feedstocks on pretreatment, hydrolysis and co-fermentation efficacy

Traditionally lignocellulosic ethanol is produced from a single raw material, but there are several reasons for using mixed raw material inputs. A broader scope increase availability of feedstocks and alleviate supply issues throughout the year. Further, the raw material costs constitute a significant part of the production cost, which directly affects profitability. Through allowing for mixed feedstock in the process a plant can hedge its sensitivity towards changes in feedstock availability and prices. Agricultural residues, like wheat straw and corn stover, share similar properties and the pretreatment parameters for optimal enzymatic hydrolysis are in the same range, with regard to temperature, pH and catalysts. These raw materials could be suitable for co-pretreatment.

In the current study mixed feedstocks consisting of wheat straw and corn stover in different ratios were investigated. Differences in composition and optimal pretreatment conditions increases the complexity of the pretreatment and the sequential hydrolysis and co-fermentation. In order to investigate the influence of mixed feedstocks, different pretreatment conditions and fermentation strategies were evaluated. The aim was to identify potential synergistic effects and obtain ethanol yields for a broad scope of mixtures of the feedstocks that were comparable to the yields for the single feedstocks processed at their respective optimal conditions.

The obtained results showed that wheat straw and corn stover could be successfully co-pretreated and the pretreated mixtures exhibited good enzymatic hydrolysability. The mixtures displayed similar challenges in the co-fermentation as the single feedstocks, with regard to rheology, xylose utilization and cellular redox imbalances.