Utilisation of microwave-NaOH pretreatment technology to improve performance and l-lactic acid yield from vinasse

Abstract

Pretreatment of vinasse is necessary to break down its complex wooden structure, improve the efficiency of enzymolysis, and provide an adequate substrate for fermentation during l -lactic acid production. Independent microwave and NaOH pretreatment processes were carried out in an earlier study. Here a two-way microwave-NaOH coupled method, was investigated to determine the effects of simultaneous saccharification and fermentation (SSF) of vinasse on l -lactic acid production. Compared with the former individual microwave and NaOH pretreatment methods, hemicellulose and lignin in vinasse were more significantly reduced using microwave-NaOH coupled pretreatments, reducing crystallinity to 14.77%. l -lactic acid yield was also higher in the coupled method than the sum of the yields from the independent pretreatment processes. The optimal conditions for the coupled pretreatment method were: 0.06 g g−1 (vinasse dry weight) NaOH; 523 W microwave power; 1:2 solid–liquid ratio; and 8 min microwave pretreatment time. These conditions resulted in an 86.0 mg g−1 l -lactic acid yield. The microwave power and the amount of alkali used were approximately 25% lower than those used prior to the optimisation process. The reduced values indicate that optimisation can significantly decrease energy and reagent consumptions. Thus, microwave-NaOH coupled pretreatment exhibits a synergistic effect for improving l -lactic acid production.