2-02: Enhancement in enzymatic hydrolysis by mechanical refining of pretreated biomass

Enzymatic hydrolysis still remains an expensive process and thus, the amount of enzyme dosage must be reduced to make the overall process more financially attractive.  Mechanical refining of biomass has been suggested as a viable strategy to reduce enzyme dosage and enhance digestibility of pretreated biomass.  This proven technology can be applied to any types of biomass and pretreatment to reduce pretreatment severity, which could help the downstream biological process.  In addition, the economic benefit can be maximized since the cost of enzyme saving is greater than the operation cost of mechanical refining.  We have tested mild-alkaline pretreated hardwood/ softwood/ corn stover, auto-hydrolysis pretreated sweet sorghum bagasse, and dilute-acid pretreated corn stover to evaluate the benefits by mechanical refining.  It was found that the mechanical refining enhanced sugar recovery of all pretreated biomass.  Enzymatic sugar recovery of alkaline pretreated hardwood increased from 55.9% to 81.9% with 5 FPU/g after mechanical refining.  Enzyme reduction of more than 50% was achieved at the same level of sugar recovery.  Sugar recoveries of alkaline pretreated corn stover and auto-hydrolyzed sweet sorghum bagasse increased by 10.5% and 35.8% by refining, respectively.  To investigate the reason for increased digestibility, pore-volume and surface area were evaluated in a wet state using three independent analyses; Water retention value, Simons’ staining, and DSC thermoporometry methods.  A strong correlation was found between sugar recovery and measured properties.  In addition, we will demonstrate how different refining actions such as fibrillation and particle size reduction affect the digestibility of pretreated biomass.