Self-Sufficient Bioethanol Production System Using a Lignin-Derived Adsorbent of Fermentation Inhibitors

We have developed a new self-sufficient bioethanol producing system that suppresses the inhibition of fermentation by thermally processed residual lignin in a separate hydrolysis and fermentation (SHF) and one-pot simultaneous saccharification and cofermentation (SSCF). The new fermentation process incorporates detoxification with the lignin-derived adsorbent; thus, needs no purchased adsorbent, produces no waste adsorbent and relieves wastewater treatment load. Eucalyptus globulus wood was pretreated by microwave (MW)-assisted hydrothermolysis in aqueous maleic acid and separated into soluble and insoluble fractions. The insoluble fraction was hydrolyzed with cellulolytic enzymes, and the residual lignin was separated. We found that thermal processing of the lignin under a normoxic atmosphere efficiently adsorbed fermentation inhibitors without affecting monosaccharide concentration by enzymatic saccharification. The processing was achieved at 250-350 degrees C, which are much lower temperatures for wood charcoal production and resulted in higher yields of the adsorbent. The residual lignin formed after SSCF was also converted to the selective adsorbent. Using the lignin-derived adsorbent and genetically engineered Zymomonas mobiliz, bioethanol was produced at 54 g/L from the pretreated biomass mash by one-pot SSCF processes coupled with prehydrolysis. The lignin-derived adsorbent is recyclable and potentially applicable to a wide range of fermentation processes of lignocellulosics.