Conversion of lignocellulosic agave residues into liquid biofuels using an AFEX™-based biorefinery

Abstract

BackgroundAgave-based alcoholic beverage companies generate thousands of tons of solid residues per year in Mexico. These agave residues might be used for biofuel production due to their abundance and favorable sustainability characteristics. In this work, agave leaf and bagasse residues from species Agave tequilana and Agave salmiana were subjected to pretreatment using the ammonia fiber expansion (AFEX) process. The pretreatment conditions were optimized using a response surface design methodology. We also identified commercial enzyme mixtures that maximize sugar yields for AFEX-pretreated agave bagasse and leaf matter, at ~ 6% glucan (w/w) loading enzymatic hydrolysis. Finally, the pretreated agave hydrolysates (at a total solids loading of ~ 20%) were used for ethanol fermentation using the glucose- and xylose-consuming strain Saccharomyces cerevisiae 424A (LNH-ST), to determine ethanol yields at industrially relevant conditions.ResultsLow-severity AFEX pretreatment conditions are required (100–120 °C) to enable efficient enzymatic deconstruction of the agave cell wall. These studies showed that AFEX-pretreated A. tequilana bagasse, A. tequilana leaf fiber, and A. salmiana bagasse gave ~ 85% sugar conversion during enzyme hydrolysis and over 90% metabolic yields of ethanol during fermentation without any washing step or nutrient supplementation. On the other hand, although lignocellulosic A. salmiana leaf gave high sugar conversions, the hydrolysate could not be fermented at high solids loadings, apparently due to the presence of natural inhibitory compounds.ConclusionsThese results show that AFEX-pretreated agave residues can be effectively hydrolyzed at high solids loading using an optimized commercial enzyme cocktail (at 25 mg protein/g glucan) producing > 85% sugar conversions and over 40 g/L bioethanol titers. These results show that AFEX technology has considerable potential to convert lignocellulosic agave residues to bio-based fuels and chemicals in a biorefinery.Electronic supplementary materialThe online version of this article (10.1186/s13068-017-0995-6) contains supplementary material, which is available to authorized users.

Rye and Oat Agricultural Wastes as Substrate Candidates for Biomass Production of the Non-Conventional Yeast Yarrowia lipolytica

“…Genetically engineered Saccharomyces cerevisiae was used for fermentations on different liquor wheat straw hydrolysates [8]. Conversion of agave residues into liquid biofuels was a subject of research as well [9]. Moreover, Y. lipolytica yeast grown in rice bran hydrolysate [10] or sugarcane bagasse hydrolysate was used for fermentation [11].…”

Aqueous Ammonia Pre-treatment of Wheat Straw: Process Optimization and Broad Spectrum Dye Adsorption on Nitrogen-Containing Lignin

“…Due to its alkalinity and volatility, ammonia is a plausible option as a reusable chemical catalyst. In addition to the processes using anhydrous or low-moisture ammonia (Cayetano and Kim, 2017, 2018; Mittal et al, 2017; Flores-Gómez et al, 2018; Guo et al, 2018; Sakuragi et al, 2018; Zhou et al, 2018), aqueous ammonia pre-treatments have been studied intensively in recent years (Sipponen, 2015; Domanski et al, 2016; Phitsuwan et al, 2016; Chong et al, 2017; Li et al, 2017; Niemi et al, 2017; Tolbert et al, 2017; Yoo et al, 2017; Du et al, 2018; Huo et al, 2018; Zhu et al, 2018; An et al, 2019; Xiao et al, 2019). In contrast to anhydrous ammonia, pre-treatment of plant biomass with aqueous ammonia dissolves lignin that can be isolated from the spent cooking liquor.…”

Agave By-Products: An Overview of Their Nutraceutical Value, Current Applications, and Processing Methods

“…In the latter process, the stems are scrapped to obtain the sap and the fibers (bagasse) that come out and are considered waste and discarded. An estimated amount of 7,710,520 tons of residual bagasse were generated from 1995 to 2019 [4], which could have applications as compost [20], silage [21], and bioethanol and methane production [19,[22][23][24][25][26][27][28], among other uses. Furthermore, bagasse is an excellent source of fibers, bioactive compounds (saponins, fructans, and phenolic compounds), sugars, and other valuable biomolecules that can be recovered from this residue [24,[29][30][31][32][33][34].…”