Overcoming factors limiting high-solids fermentation of lignocellulosic biomass to ethanol

Abstract

Simultaneous saccharification and fermentation (SSF) of solid biomass can reduce the complexity and improve the economics of lignocellulosic ethanol production by consolidating process steps and reducing end-product inhibition of enzymes compared with separate hydrolysis and fermentation (SHF). However, a long-standing limitation of SSF has been too low ethanol yields at the high-solids loading of biomass needed during fermentation to realize sufficiently high ethanol titers favorable for more economical ethanol recovery. Here, we illustrate how competing factors that limit ethanol yields during high-solids fermentations are overcome by integrating newly developed cosolvent-enhanced lignocellulosic fractionation (CELF) pretreatment with SSF. First, fed-batch glucose fermentations by DA revealed that this strain, which has been favored for SSF, can produce ethanol at titers of up to 86 g⋅L Then, optimizing SSF of CELF-pretreated corn stover achieved unprecedented ethanol titers of 79.2, 81.3, and 85.6 g⋅L in batch shake flask, corresponding to ethanol yields of 90.5%, 86.1%, and 80.8% at solids loadings of 20.0 wt %, 21.5 wt %, and 23.0 wt %, respectively. Ethanol yields remained at over 90% despite reducing enzyme loading to only 10 mg protein⋅g glucan [∼6.5 filter paper units (FPU)], revealing that the enduring factors limiting further ethanol production were reduced cell viability and glucose uptake by DA and not loss of enzyme activity or mixing issues, thereby demonstrating an SSF-based process that was limited by a strain's metabolic capabilities and tolerance to ethanol.

Improved enzymatic hydrolysis and ethanol production by combined alkaline peroxide and ionic liquid‐water mixtures pretreatment of rice straw

“…The conversion ratio was higher than the reported literature . However, the fermentation efficiency was dramatically reduced with the increase of solid loadings and was slightly inferior to that reported in the literature . It was speculated that fermentation inhibitors such as various organic acids accumulated gradually during the process of SScF and the high viscosity could also cause loss of efficiency.…”

“…24 However, the fermentation efficiency was dramatically reduced with the increase of solid loadings and was slightly inferior to that reported in the literature. 17,41 It was speculated that fermentation inhibitors such as various organic acids accumulated gradually during the process of SScF and the high viscosity could also cause loss of efficiency. An effective method for high solids fed-batch enzymolysis of sugarcane bagasse based on system viscosity changes has been developed and could alleviate the high viscosity problem.…”

Influence of reactors, microbial carbohydrate uptake, and metabolic pathways on ethanol production from grass biomass: A review

“…Enzymatic hydrolysis is followed by fermentation, which is a chemical process for converting simple monomeric sugars such as glucose and xylose to produce ethanol with the evolution of CO 2 via glucose and xylose utilizing pathways. Researchers have developed different modes of fermentation that includes batch, fed batch, and continuous operations depending on the quantitative ratio of the end products and direction of fermentation along with the characteristics of the fermenting microorganisms . Bioethanol production from perennial crop could be a promising technology if an appropriate fermentation technique is applied.…”

“…Researchers have developed different modes of fermentation that includes batch, fed batch, and continuous operations depending on the quantitative ratio of the end products and direction of fermentation along with the characteristics of the fermenting microorganisms. 27 Bioethanol production from perennial crop could be a promising technology if an appropriate fermentation technique is applied. However, in order to achieve high ethanol titres from grass biomass, it is imperative to understand two vital points, ie, influence of fermentation parameters on microorganisms and the response of microorganisms to those parameters.…”

Performance of three delignifying pretreatments on hardwoods: hydrolysis yields, comprehensive mass balances, and lignin properties

“…Building on these previous studies, the goal of the work presented here was to compare the performance of three pretreatments: (1) an acidic solvolysis pretreatment employing THF and water co-solvents (co-solventenhanced lignocellulosic fractionation, CELF) [28][29][30][31][32] (2) a high-solid loading pretreatment with the ionic liquid cholinium lysinate ([Ch][Lys]) that has the potential to be derived from lignocellulosic biomass [33][34][35][36][37], and (3) two-stage Cu-catalyzed alkaline hydrogen peroxide pretreatment (Cu-AHP) utilizing an alkaline pre-extraction followed by an Cu-catalyzed alkaline-oxidative stage [38][39][40][41][42]. The efficacy of these three pretreatments was evaluated on two different hardwood feedstocks, a hybrid poplar and a eucalyptus, and the impact of pretreatment on hydrolysis yields and lignin properties, including the lignin's susceptibility to depolymerization, was assessed.…”