Lactic acid production from lignocellulosic residues: A case study towards process integration

Abstract

In this study, the production of lactic acid from municipal forestry and greening wastes processed by steam explosion and enzymatic hydrolysis was addressed. The prehydrolyzate after filtration of the steam exploded slurry, previously detoxified, and the enzymatic hydrolyzate from the insoluble solid fraction were studied as broths for lactic acid fermentation using Lactobacillus rhamnosus and Bacillus coagulans. The fermentation of the enzymatic hydrolysate was successful using both microorganisms with similar product yields around 0.9 (g/g, based on consumed glucose). The utilization of the detoxified prehydrolyzate showed the necessity of a dilution for B .coagulans to grow and ferment glucose and xylose, while L. rhamnosus was able to grow, but to assimilate only glucose. The best integrated strategy using both streams was the fermentation with B. coagulans of the prehydrolyzate diluted with the enzymatic hydrolyzate in a 1:3 ratio, yielding 0.93 g lactic acid/g glucose consumed and a lactic acid concentration of 46 g L-1