The biochemical conversion of cellulosic biomass to ethanol, a promising alternative fuel, can be carried out efficiently and economically using the simultaneous saccharification and fermentation (SSF) process. The SSF integrates the enzymatic hydrolysis of cellulose to glucose, catalyzed by the synergistic action of cellulase and P-glucosidase, with the fermentative synthesis of ethanol. Because the enzymatic step determines the availability of glucose to the ethanologenic fermentation, the kinetics of cellulose hydrolysis by cellulase and p-glucosidase and the susceptibility of the two enzymes to inhibition by hydrolysis and fermentation products are of significant importance to the SSF performance and were investigated under realistic SSF conditions. A previously developed SSF mathematical model was used to conceptualize the depolymerization of cellulose. The model was regressed to the collected data to determine the values of the enzyme parameters and was found to satisfactorily predict the kinetics of cellulose hydrolysis. Cellobiose and glucose were identified as the strongest inhibitors of cellulase and P-glucosidase, respectively. Experimental and modeling results are presented in light of the impact of enzymatic hydrolysis on fuel ethanol production.
Ethanol from cellulosic biomass is a promising renewable liquid transportation fuel. Applied research in the area of biomass conversion to ethanol in the last 20 years has answered most of the major challenges on the road to commercialization but, as with any new technology, there is still room for performance improvement. A verified mathematical model was used to examine the most critical biochemical engineering aspects of ethanol production in this study. Extensive simulations of the simultaneous saccharification and fermentation (SSF) of cellulose were conducted to identify the effects of operating conditions, pretreatment effectiveness, microorganism parameters, and enzyme characteristics on ethanol production. The results clearly show that the biomass-enzyme interaction plays a dominant role in determining the performance of SSF in batch and continuous operating modes. In particular, the digestibility of the substrate (as a result of pretreatment) and the cellulase enzyme dosage, specific activity, and composition had a profound effect on ethanol yield. This investigation verified the conclusion that R&D emphasis should be placed on developing more effective pretreatment methods and producing cellulase preparations of high specific activity (low cost per enzyme unit) to realize gains from any development of advanced hexose/pentose-fermenting organisms.
Oleaginous microalgae and yeasts represent promising candidates for large-scale production of lipids, which can be utilized for production of drop-in biofuels, nutraceuticals, pigments, and cosmetics. However, low lipid productivity and costly downstream processing continue to hamper the commercial deployment of oleaginous microorganisms. Strain improvement can play an essential role in the development of such industrial microorganisms by increasing lipid production and hence reducing production costs. The main means of strain improvement are random mutagenesis, adaptive laboratory evolution (ALE), and rational genetic engineering. Among these, random mutagenesis and ALE are straight forward, low-cost, and do not require thorough knowledge of the microorganism’s genetic composition. This paper reviews available mutagenesis and ALE techniques and screening methods to effectively select for oleaginous microalgae and yeasts with enhanced lipid yield and understand the alterations caused to metabolic pathways, which could subsequently serve as the basis for further targeted genetic engineering.
Brassica carinata or Ethiopian mustard, a non‐edible oilseed brassica, is a low carbon, purpose‐grown, and none‐to‐low indirect land‐use change bioenergy feedstock for the production of drop‐in sustainable aviation fuel, biodiesel, renewable diesel, and a suite of value‐added coproducts. Carinata oil converted to drop‐in fuel using an American Society for Testing and Materials approved Catalytic Hydrothermolysis process has been successfully tested in commercial and military aviation. Carinata meal, the residue after oil extraction, is a high‐protein feed supplement for livestock, poultry, and swine, and can also yield specialty products. The Southeast Partnership for Advanced Renewables from Carinata (SPARC) is a public–private partnership formed with a twofold mission: (1) Removing physical, environmental, social, and economic constraints that prevent regional intensification of carinata production as a low‐carbon feedstock for renewable fuel and coproducts and (2) demonstrating enhanced value across the entire value chain by mitigating risk to farmers and other stakeholders. The partnership's goal is to energize the US bioeconomy through sustainable agriculture and thus contribute to energy security and economic diversification. SPARC relies on a combination of cutting‐edge multidisciplinary research and active industry engagement to facilitate adoption of the crop. This involves informing stakeholders along the entire supply chain, from producers to end‐users, policymakers, influencers, and the public, about the opportunities and best practices related to carinata. This article provides context and background concerning carinata commercialization as a winter cash crop in the Southeast US for renewable fuels and bioproducts. The advances made to date in the areas of feedstock development, fuel and coproduct development, meal valorization, supply chain logistics, and stakeholder engagement are outlined.
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