Urvi D. Kothari and Y. Y. Lee. Department of Chemical Engineering, Auburn University, 212 Ross Hall, Auburn University, Auburn, AL 36849-5127
The effects of dilute acid pretreatment liquor on enzymatic hydrolysis of lignocellulosic biomass and microbial conversion to ethanol production were investigated. The treatment of biomass with acid removes the hemicellulose portion along with degradation and extraneous components that are potentially toxic to biological reactions. For the cellulosic ethanol process to be economically feasible, cellulose as well as hemicellulose must be utilized. Therefore, the hydrolysates of the pretreatment containing hemicellulose sugars need to be co-processed with the pretreated solid during the bioconversion process. In this work, the prehydrolyzates from dilute-acid treatment of corn stover were added to a SSCF reactor converting Solka Floc to ethanol in order to verify its inhibition effects. The enzymatic reaction was inhibited significantly reducing the reaction rate by 65% with 1:1 mix. The toxic effect on the microorganism was even higher showing negligible ethanol production in the SSCF. This inhibition effect was further studied to identify the individual inhibition effect and the type of inhibition on the enzyme. Inhibition by individual component of HMF, furfural and xylose at concentrations normally found in the prehydrolyzate was found to be much lower than that of the liquor from the acid pretreatment. The inhibition is therefore caused primarily by the organic acids, acid soluble lignin, and its degradation products. The inhibition data of these components on the enzymatic reaction and the toxic effects on the microbial growth and cellular reactions are analyzed, and the individual and conjugate effects are discussed.
