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

Abstract

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 °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.

Production and Application of Lignin-Based Chemicals and Materials in the Cellulosic Ethanol Production: An Overview on Lignin Closed-Loop Biorefinery Approaches

“…These results imply that AC from lignin can be competitive compared to commercial AC. Similar reports were observed in Yoshioka et al [185]. They developed an in situ detoxification with AC from lignin for ethanol production from E. globulus wood.…”

“…These studies make it clear that lignin residues are attractive options for the production of AC even because the biopolymer has a high carbon content (around 50-60%) [76] and the polysaccharide fraction is converted into products. The integration of the currents generates a scenario of self-sufficiency, in which the purchase of commercial adsorbents is dispensable, reduces the waste generation, and takes advantage of the energy of the soluble inhibitors (since the saturated activated carbon can be burned) [185]. Comparing prices between commercial AC (~ $0.5-$1.5/kg) and the AC obtained from lignin residues is complicated.…”

“…Among the proposals shown, we believe that there is a greater chance of success with the approaches using lignin-based activated carbon, lignin-based surfactants, and lignins as enzyme immobilization support. The addition of lignin-based activated carbon can eliminate the presence of furans and hydrolyzed phenolic compounds and can trigger the scheme to finally reach attractive ethanol titers (see Yoshioka et al [185]). The preparation of lignin-based surfactants based and enzymes immobilized on lignin supports involves simple reactions so that steps of lignin depolymerization and separation of monomers are discarded; also, these approaches lead to reduced enzyme consumption, as mentioned in Sects.…”

Xylose-Enriched Ethanol Fermentation Stillage from Sweet Sorghum for Xylitol and Astaxanthin Production

“…A previous hydrolysate generated from pretreated SSB that was not subjected to ethanol fermentation and therefore contained a mixture of glucose, xylose, and arabinose exhibited a similar increase in astaxanthin output after detoxification [25]. It is assumed that soluble aromatic compounds originating from lignin are the primary cause for product inhibitory effects during yeast fermentation [41,42]. However, the inhibition exhibited by P. rhodozyma is slightly different as the astaxanthin output by the yeast strain was affected and not biomass growth.…”

Cross-Linked Polyethylenimine for Selective Adsorption and Effective Recovery of Lignocellulose-Derived Organic Acids and Aldehydes

“…In addition to organic acids, the furan aldehydes can also coexist with sugars (e.g., glucose, xylose, and fructose) in the reaction solutions and the pretreated lignocelluloses. 15,25,27,28,[33][34][35][36][37][38]46,47 Ideally, an adsorbent should only adsorb the nonsugar solutes (i.e., aldehydes and organic acids) but maximally retain sugars, which is particularly important when applied to remove the fermentation inhibitors. 6−13 Several studies have shown that the PEI usually shows negligible adsorption of sugars.…”