Nitrogen Sources Screening for Ethanol Production Using Carob Industrial Wastes

Lignocellulose degradation, enzymatic saccharification and bioethanol production from whole-crop sweet sorghum silage inoculated with feruloyl-esterase producing lactic acid bacteria

Commercialization of cellulosic biofuels faces challenges like year-round feedstock availability and lignocellulose recalcitrance. This study ensiled whole-crop sweet sorghum biomass, inoculating it with feruloyl-esterase producing Lactiplantibacillus plantarum A1 to ensure consistent feedstock supply and promote lignin degradation during fermentation. The ensiled biomass underwent 72 h enzymatic saccharification followed by 96 h Saccharomyces cerevisiae fermentation for bioethanol production. Compared to uninoculated controls, L. plantarum A1 inoculation significantly reduced dry matter loss, improved aerobic stability, had higher lactic acid bacteria (LAB) counts, and reduced yeast counts. Inoculation also improved fermentation quality, evidenced by lower pH (3.50 vs 3.66) and higher lactic acid concentrations (44.48 vs 23.56 g/kg DM). Proteolysis was notably reduced, indicated by decreased non-protein nitrogen fractions (P < 0.05). Inoculation enhanced lignin degradation, as shown by lower lignin content, higher ferulic acid concentrations, and disintegrated biomass structure observed via scanning electron microscopy (SEM). These improvements led to increased fermentable sugar availability post-saccharification, resulting in higher ethanol yields during S. cerevisiae fermentation. This study highlights the potential of silage inoculation with feruloyl-esterase producing L. plantarum A1 in optimizing bioethanol production from whole-crop sweet sorghum biomass at a relatively lower cost of pretreatment.

Strategic nutrient sourcing for biomanufacturing intensification

The successful design of economically viable bioprocesses can help to abate global dependence on petroleum, increase supply chain resilience, and add value to agriculture. Specifically, bioprocessing provides the opportunity to replace petrochemical production methods with biological methods and to develop novel bioproducts. Even though a vast range of chemicals can be biomanufactured, the constraints on economic viability, especially while competing with petrochemicals, are severe. There have been extensive gains in our ability to engineer microbes for improved production metrics and utilization of target carbon sources. The impact of growth medium composition on process cost and organism performance receives less attention in the literature than organism engineering efforts, with media optimization often being performed in proprietary settings. The widespread use of corn steep liquor as a nutrient source demonstrates the viability and importance of "waste" streams in biomanufacturing. There are other promising waste streams that can be used to increase the sustainability of biomanufacturing, such as the use of urea instead of fossil fuel-intensive ammonia and the use of struvite instead of contributing to the depletion of phosphate reserves. In this review, we discuss several process-specific optimizations of micronutrients that increased product titers by twofold or more. This practice of deliberate and thoughtful sourcing and adjustment of nutrients can substantially impact process metrics. Yet the mechanisms are rarely explored, making it difficult to generalize the results to other processes. In this review, we will discuss examples of nutrient sourcing and adjustment as a means of process improvement.

ONE-SENTENCE SUMMARY

The potential impact of nutrient adjustments on bioprocess performance, economics, and waste valorization is undervalued and largely undercharacterized.

Bioethanol Production from Cellulose-Rich Corncob Residue by the Thermotolerant Saccharomyces cerevisiae TC-5

This study aimed to select thermotolerant yeast for bioethanol production from cellulose-rich corncob (CRC) residue. An effective yeast strain was identified as Saccharomyces cerevisiae TC-5. Bioethanol production from CRC residue via separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), and prehydrolysis-SSF (pre-SSF) using this strain were examined at 35-42 °C compared with the use of commercial S. cerevisiae. Temperatures up to 40 °C did not affect ethanol production by TC-5. The ethanol concentration obtained via the commercial S. cerevisiae decreased with increasing temperatures. The highest bioethanol concentrations obtained via SHF, SSF, and pre-SSF at 35-40 °C of strain TC-5 were not significantly different (20.13-21.64 g/L). The SSF process, with the highest ethanol productivity (0.291 g/L/h), was chosen to study the effect of solid loading at 40 °C. A CRC level of 12.5% (w/v) via fed-batch SSF resulted in the highest ethanol concentrations of 38.23 g/L. Thereafter, bioethanol production via fed-batch SSF with 12.5% (w/v) CRC was performed in 5-L bioreactor. The maximum ethanol concentration and ethanol productivity values were 31.96 g/L and 0.222 g/L/h, respectively. The thermotolerant S. cerevisiae TC-5 is promising yeast for bioethanol production under elevated temperatures via SSF and the use of second-generation substrates.

Cellulosic Bioethanol from Industrial Eucalyptus globulus Bark Residues Using Kraft Pulping as a Pretreatment

The pulp and paper industry faces an emerging challenge for valorising wastes and side-streams generated according to the biorefinery concept. Eucalyptus globulus bark, an abundant industrial residue in the Portuguese pulp and paper sector, has a high potential to be converted into biobased products instead of being burned. This work aimed to evaluate the ethanol production from E. globulus bark previously submitted to kraft pulping through separate hydrolysis and fermentation (SHF) configuration. Fed-batch enzymatic hydrolysis provided a concentrated hydrolysate with 161.6 g·L−1 of cellulosic sugars. S. cerevisiae and Ethanol Red® strains demonstrated a very good fermentation performance, despite a negligible xylose consumption. S. passalidarum, a yeast known for its capability to consume pentoses, was studied in a simultaneous co-culture with Ethanol Red®. However, bioethanol production was not improved. The best fermentation performance was achieved by Ethanol Red®, which provided a maximum ethanol concentration near 50 g·L−1 and fermentation efficiency of 80%. Concluding, kraft pulp from E. globulus bark showed a high potential to be converted into cellulosic bioethanol, being susceptible to implementing an integrated biorefinery on the pulp and paper industrial plants.

Using agro-industrial wastes for mixotrophic growth and lipids production by the green microalga Chlorella sorokiniana

There has been growing interest in the use of microalgae for the production of biofuels, but production costs continue to be too high to compete with fossil fuel prices. One of the main limitations for photobioreactor productivity is light shielding, especially at high cell densities. The growth of the green microalga Chlorella sorokiniana, a robust industrial species, has been evaluated under different trophic conditions with traditional carbon sources, such as glucose and sucrose, and alternative low cost carbon sources, such as carob pod extract, industrial glycerol and acetate-rich oxidized wine waste lees. The mixotrophic cultivation of this microalga with wine waste lees alleviated the problems of light shielding observed in photoautotrophic cultures, improving specific growth rate (0.052 h^-1) compared with the other organic sources. The fed-batch mixotrophic culture of Chlorella sorokiniana in a 2 L stirred tank reactor, with optimized nutritional conditions, 100 mM of acetate coming from the oxidized wine waste lees and 30 mM of ammonium, produced an algal biomass concentration of 11 g L^-1 with a lipid content of 38 % (w/w). This fed-batch strategy has been found to be a very effective means to enhance the biomass and neutral lipid productivity.

Efficacy of ionic liquids on the growth and simultaneous xylanase production by Sporotrichum thermophile: membrane integrity, composition and morphological investigation

Ionic liquids (ILs) are emerging as promising solvent systems for carrying out various biochemical reactions.