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

Developing integrated biorefineries requires the generation of high-value co-products produced alongside cellulosic ethanol. Most industrial yeast strains produce ethanol at high titers, but the small profit margins for generating ethanol require that additional high-value chemicals be generated to improve revenue. The aim of this research was to boost xylose utilization and conversion to high-value co-products that can be generated in an integrated biorefinery. Pretreated sweet sorghum bagasse (SSB) was hydrolyzed in sweet sorghum juice (SSJ) followed by ethanol fermentation. Ethanol was removed from the fermentation broth by evaporation to generate a stillage media enriched in xylose. Candida mogii NRRL Y-17032 could easily grow in non-detoxified stillage media, but a high xylitol yield of 0.55 g xylitol/g xylose consumed was achieved after recovered cells were resuspended in synthetic media containing supplemented xylose. Phaffia rhodozyma ATCC 74219 could be cultivated in non-detoxified stillage media, but astaxanthin generation was increased 4-fold (from 17.5 to 71.7 mg/L) in detoxified media. Future processing strategies to boost product output should focus on a two-step process where the stillage media is used as the growth stage, and a synthetic media for the production stage utilizing xylose generated from SSB through selective hemicellulase enzymes

Utilization of Sweet Sorghum Juice for the Production of Astaxanthin as a Biorefinery Co-Product by <i>Phaffia rhodozyma</i>

This work investigates cultivating the red-pigmented yeast Phaffia rhodozyma in sweet sorghum juice (SSJ) to assess the production of astaxanthin as a potential biorefinery co-product. Shake flask cultures on defined sugar medium indicated that all three sugars (sucrose, glucose, and fructose) could be consumed with adequate nitrogen and nutrient supplementation. Only modest biomass growth and astaxanthin production could be achieved in SSJ without nitrogen supplementation; however, combining nitrogen supplementation with yeast extract in diluted SSJ could metabolize all sugars present in 168 h. A 2 L bioreactor trial with full strength (i.e., undiluted) SSJ produced up to 29 g/L of biomass, 65.4 mg/L of astaxanthin, an overall cell astaxanthin content of 2.49 mg astaxanthin/g dry cell mass, and a volumetric astaxanthin productivity of 0.389 mg/L/h after 168 h of cultivation. Further process optimization is needed since glucose metabolism was incomplete in undiluted SSJ

Conversion of corn stover alkaline pre-treatment waste streams into biodiesel via Rhodococci

The bioconversion of second-generation cellulosic ethanol waste streams into biodiesel via oleaginous bacteria, Rhodococcus, is a novel optimization strategy for biorefineries with substantial potential for rapid development.</p

Integrated experimental and technoeconomic evaluation of two-stage Cu-catalyzed alkaline–oxidative pretreatment of hybrid poplar

Abstract Background When applied to recalcitrant lignocellulosic feedstocks, multi-stage pretreatments can provide more processing flexibility to optimize or balance process outcomes such as increasing delignification, preserving hemicellulose, and maximizing enzymatic hydrolysis yields. We previously reported that adding an alkaline pre-extraction step to a copper-catalyzed alkaline hydrogen peroxide (Cu-AHP) pretreatment process resulted in improved sugar yields, but the process still utilized relatively high chemical inputs (catalyst and H2O2) and enzyme loadings. We hypothesized that by increasing the temperature of the alkaline pre-extraction step in water or ethanol, we could reduce the inputs required during Cu-AHP pretreatment and enzymatic hydrolysis without significant loss in sugar yield. We also performed technoeconomic analysis to determine if ethanol or water was the more cost-effective solvent during alkaline pre-extraction and if the expense associated with increasing the temperature was economically justified. Results After Cu-AHP pretreatment of 120 °C NaOH-H2O pre-extracted and 120 °C NaOH-EtOH pre-extracted biomass, approximately 1.4-fold more total lignin was solubilized (78% and 74%, respectively) compared to the 30 °C NaOH-H2O pre-extraction (55%) carried out in a previous study. Consequently, increasing the temperature of the alkaline pre-extraction step to 120 °C in both ethanol and water allowed us to decrease bipyridine and H2O2 during Cu-AHP and enzymes during hydrolysis with only a small reduction in sugar yields compared to 30 °C alkaline pre-extraction. Technoeconomic analysis indicated that 120 °C NaOH-H2O pre-extraction has the lowest installed ($246 million) and raw material ($175 million) costs compared to the other process configurations. Conclusions We found that by increasing the temperature of the alkaline pre-extraction step, we could successfully lower the inputs for pretreatment and enzymatic hydrolysis. Based on sugar yields as well as capital, feedstock, and operating costs, 120 °C NaOH-H2O pre-extraction was superior to both 120 °C NaOH-EtOH and 30 °C NaOH-H2O pre-extraction