(421ag) AHP Pretreatment, High Solid Loading Enzymatic Hydrolysis and Fermentation of Switchgrass for Ethanol Production

In this study, AHP pretreatment conditions, enzymatic hydrolysis and ethanol fermentation of switchgrass were investigated. Compare to different concentration of NaOH, to adjust the pH at 11.5 constantly during pretreatment can significantly enhance the efficient of bioconvertion from switchgrass to fermentable sugars such as glucose and xylose. Under this condition, the digestibility can reach 70%. The optimal conditions of enzymatic hydrolysis were using mixture of accelerase, xylanase and pectinase by the enzyme protein ratio of 63:27:10. The enzymatic hydrolysis conducted under this condition can get much higher xylose yield, which is 3 times of the yield before optimization.

In fermentation step, comparison of different strains,  Pichia stipitis CBS 6054, Saccharomyces cerevisiae GLBRC Y35, GLBRC 76 and 77 were tested.  Meanwhile, different hydrolyzates were used in this study, which were detoxified (by using activated carbon), undetoxified enzymatic hydrolyzates, hydrolyzates with and without washing after pretreatment,  hydrolyzate got from pretreated biomass with H₂SO₄ adjusting pH to 4.6-4.8 followed by enzymatic hydrolysis. The results showed that during pretreatment some inorganic (sodium from NaOH and sulfate used for pH adjustment)  and organic (aromatics which were derived from lignin, acetate which came from hemicellulose, and other oxidation products such as aliphatic carboxylic acids)  inhibitors could be generated. p-coumaric acid and ferulic acid  are components of lignin in grasses, which can go into solutions under alkaline conditions and also can be removed by activated carbon.  Process integration challenges AHP pretreatment at higher solids loadings which are necessary for producing ethanol of high titers as concentrations of these soluble fermentation inhibitors increase simultaneously.