Integrated biorefinery approaches for the industrialization of cellulosic ethanol fuel

Composition of Lignocellulose Hydrolysate in Different Biorefinery Strategies: Nutrients and Inhibitors

The hydrolysis and biotransformation of lignocellulose, i.e., biorefinery, can provide human beings with biofuels, bio-based chemicals, and materials, and is an important technology to solve the fossil energy crisis and promote global sustainable development. Biorefinery involves steps such as pretreatment, saccharification, and fermentation, and researchers have developed a variety of biorefinery strategies to optimize the process and reduce process costs in recent years. Lignocellulosic hydrolysates are platforms that connect the saccharification process and downstream fermentation. The hydrolysate composition is closely related to biomass raw materials, the pretreatment process, and the choice of biorefining strategies, and provides not only nutrients but also possible inhibitors for downstream fermentation. In this review, we summarized the effects of each stage of lignocellulosic biorefinery on nutrients and possible inhibitors, analyzed the huge differences in nutrient retention and inhibitor generation among various biorefinery strategies, and emphasized that all steps in lignocellulose biorefinery need to be considered comprehensively to achieve maximum nutrient retention and optimal control of inhibitors at low cost, to provide a reference for the development of biomass energy and chemicals.

Advanced biofuel production, policy and technological implementation of nano-additives for sustainable environmental management - A critical review

This review article critically evaluates the significance of adopting advanced biofuel production techniques that employ lignocellulosic materials, waste biomass, and cutting-edge technology, to achieve sustainable environmental stewardship. Through the analysis of conducted research and development initiatives, the study highlights the potential of these techniques in addressing the challenges of feedstock supply and environmental impact and implementation policies that have historically plagued the conventional biofuel industry. The integration of state-of-the-art technologies, such as nanotechnology, pre-treatments and enzymatic processes, has shown considerable promise in enhancing the productivity, quality, and environmental performance of biofuel production. These developments have improved conversion methods, feedstock efficiency, and reduced environmental impacts. They aid in creating a greener and sustainable future by encouraging the adoption of sustainable feedstocks, mitigating greenhouse gas emissions, and accelerating the shift to cleaner energy sources. To realize the full potential of these techniques, continued collaboration between academia, industry representatives, and policymakers remains essential.

Engineering All-Round Cellulase for Bioethanol Production

One strategy to decrease both the consumption of crude oil and environmental damage is through the production of bioethanol from biomass. Cellulolytic enzyme stability and enzymatic hydrolysis play important roles in the bioethanol process. However, the gradually increased ethanol concentration often reduces enzyme activity and leads to inactivation, thereby limiting the final ethanol yield. Herein, we employed an optimized Two-Gene Recombination Process (2GenReP) approach to evolve the exemplary cellulase CBHI for practical bioethanol fermentation. Two all-round CBHI variants (named as R2 and R4) were obtained with simultaneously improved ethanol resistance, organic solvent inhibitor tolerance, and enzymolysis stability in simultaneous saccharification and fermentation (SSF). Notably, CBHI R4 had a 7.0- to 34.5-fold enhanced catalytic efficiency (kcat/KM) in the presence/absence of ethanol. Employing the evolved CBHI R2 and R4 in the 1G bioethanol process resulted in up to 10.27% (6.7 g/L) improved ethanol yield (ethanol concentration) than non-cellulase, which was far more beyond than other optimization strategies. Besides bioenergy fields, this transferable protein engineering routine holds the potential to generate all-round enzymes that meet the requirement in biotransformation and bioenergy fields.

Evolving Robust and Interpretable Enzymes for the Bioethanol Industry

Obtaining a robust and applicable enzyme for bioethanol production is a dream for biorefinery engineers. Herein, we describe a general method to evolve an all-round and interpretable enzyme that can be directly employed in the bioethanol industry. By integrating the transferable protein evolution strategy InSiReP 2.0 (In Silico guided Recombination Process), enzymatic characterization for actual production, and computational molecular understanding, the model cellulase PvCel5A (endoglucanase II Cel5A from Penicillium verruculosum) was successfully evolved to overcome the remaining challenges of low ethanol and temperature tolerance, which primarily limited biomass transformation and bioethanol yield. Remarkably, application of the PvCel5A variants in both first- and second-generation bioethanol production processes (i. Conventional corn ethanol fermentation combined with the in situ pretreatment process; ii. cellulosic ethanol fermentation process) resulted in a 5.7-10.1 % increase in the ethanol yield, which was unlikely to be achieved by other optimization techniques.

Enzymatic Hydrolysis Strategies for Cellulosic Sugars Production to Obtain Bioethanol from Eucalyptus globulus Bark

Cellulosic sugars production for the valorization of lignocellulosic biomass residues in an industrial site has economic benefits and is promising if integrated into a biorefinery. Enzymatic hydrolysis (EH) of pretreated Eucalyptus globulus bark, an industrial residue of low-economic value widely available in Portuguese pulp and paper mills, could be an excellent approach to attain resource circularity and pulp mill profitability. This work evaluated the potential for improving cellulosic sugars concentrations by operating with high solids loading and introducing the additives Triton X-100, PEG 4000 and Tween 80 using a commercial enzymatic consortium with a dosage of 25 FPU gcarbohydrates−1. Additives did not improve enzymatic hydrolysis performance, but the effect of increasing solids loading to 14% (w/v) in batch operation was accomplished. The fed-batch operation strategy was investigated and, when starting with 11% (w/v) solids loading, allowed the feeding of 3% (w/v) fresh feedstock sequentially at 2, 4 and 6 h, attaining 20% (w/v) total solids loading. After 24 h of operation, the concentration of cellulosic sugars reached 161 g L−1, corresponding to an EH conversion efficiency of 76%. Finally, the fermentability of the fed-batch hydrolysate using the Ethanol Red® strain was evaluated in a 5 L bioreactor scale. The present results demonstrate that Eucalyptus globulus bark, previously pretreated by kraft pulping, is a promising feedstock for cellulosic sugars production, allowing it to become the raw material for feeding a wide range of bioprocesses.

Critical review of biochemical pathways to transformation of waste and biomass into bioenergy

In recent years, biofuel or biogas have become the primary source of bio-energy, providing an alternative to conventionally used energy that can meet the growing energy demand for people all over the world while reducing greenhouse gas emissions. Enzyme hydrolysis in bioethanol production is a critical step in obtaining sugars fermented during the final fermentation process. More efficient enzymes are being researched to provide a more cost-effective technique during enzymatic hydrolysis. The exploitation of microbial catabolic biochemical reactions to produce electric energy can be used for complex renewable biomasses and organic wastes in microbial fuel cells. In hydrolysis methods, a variety of diverse enzyme strategies are used to promote efficient bioethanol production from various lignocellulosic biomasses like agricultural wastes, wood feedstocks, and sea algae. This paper investigates the most recent enzyme hydrolysis pathways, microbial fermentation, microbial fuel cells, and anaerobic digestion in the manufacture of bioethanol/bioenergy from lignocellulose biomass.

Design of biorefineries towards carbon neutrality: A critical review

The increase in worldwide demand for energy is driven by the rapid increase in population and exponential economic development. This resulted in the fast depletion of fossil fuel supplies and unprecedented levels of greenhouse gas in the atmosphere. To valorize biomass into different bioproducts, one of the popular and carbon-neutral alternatives is biorefineries. This system is an appropriate technology in the circular economy model. Various research highlighted the role of biorefineries as a centerpiece in the carbon-neutral ecosystem of technologies of the circular economy model. To fully realize this, various improvements and challenges need to be addressed. This paper presents a critical and timely review of the challenges and future direction of biorefineries as an alternative carbon-neutral energy source.

Integrating 1G with 2G Bioethanol Production by Using Distillers’ Dried Grains with Solubles (DDGS) as the Feedstock for Lignocellulolytic Enzyme Production

First-generation (1G) bioethanol is one of the most used liquid biofuels in the transport industry. It is generated by using sugar- or starch-based feedstocks, while second-generation (2G) bioethanol is generated by using lignocellulosic feedstocks. Distillers’ dried grains with solubles (DDGS) is a byproduct of first-generation bioethanol production with a current annual production of 22.6 million tons in the USA. DDGS is rich in fiber and valuable nutrients contents, which can be used to produce lignocellulolytic enzymes such as cellulases and hemicellulases for 2G bioethanol production. However, DDGS needs a pretreatment method such as dilute acid, ammonia soaking, or steam hydrolysis to release monosaccharides and short-length oligosaccharides as fermentable sugars for use in microbial media. These fermentable sugars can then induce microbial growth and enzyme production compared to only glucose or xylose in the media. In addition, selection of one or more suitable microbial strains, which work best with the DDGS for enzyme production, is also needed. Media optimization and fermentation process optimization strategies can then be applied to find the optimum conditions for the production of cellulases and hemicellulases needed for 2G bioethanol production. Therefore, in this review, a summary of all such techniques is compiled with a special focus on recent findings obtained in previous pieces of research conducted by the authors and by others in the literature. Furthermore, a comparison of such techniques applied to other feedstocks and process improvement strategies is also provided. Overall, dilute acid pretreatment is proven to be better than other pretreatment methods, and fermentation optimization strategies can enhance enzyme production by considerable folds with a suitable feedstock such as DDGS. Future studies can be further enhanced by the technoeconomic viability of DDGS as the on-site enzyme feedstock for the manufacture of second-generation bioethanol (2G) in first-generation (1G) ethanol plants, thus bridging the two processes for the efficient production of bioethanol using corn or other starch-based lignocellulosic plants.

Increasing extracellular cellulase activity of the recombinant Saccharomyces cerevisiae by engineering cell wall-related proteins for improved consolidated processing of carbon neutral lignocellulosic biomass

Sustainable bioproduction usingcarbon neutral feedstocks, especially lignocellulosic biomass, has attracted increasing attention due to concern over climate change and carbon reduction. Consolidated bioprocessing (CBP) of lignocellulosic biomass using recombinantyeast of Saccharomyces cerevisiaeis a promising strategy forlignocellulosic biorefinery. However, the economic viability is restricted by low enzyme secretion levels.For more efficient CBP, MIG1_spsc01isolated from the industrial yeast which encodes the glucose repression regulator derivative was overexpressed. Increased extracellular cellobiohydrolase (CBH) activity was observed with unexpectedly decreased cell wall integrity. Further studies revealed that disruption ofCWP2, YGP1, andUTH1,which are functionally related toMIG1_spsc01, also enhanced CBH secretion. Subsequently, improved cellulase production was achieved by simultaneous disruption ofYGP1and overexpression ofSED5, which remarkably increased extracellular CBH activity of 2.2-fold over the control strain. These results provide a novel strategy to improve the CBP yeast for bioconversion of carbon neutral biomass.

Process design and techno-economic analysis of fuel ethanol production from food waste by enzymatic hydrolysis and fermentation

In this study, fuel ethanol production from food waste using enzymatic hydrolysis and fermentation was evaluated from techno-economic viewpoint. The plant was designed with a capacity of 10 t/d food waste and a lifetime of 15-year. The total capital cost, annual operation cost and annual net profits of the plant were US$ 367,552, US$ 155,959 and US$ 74,995.57, respectively. The plant was economically viable as long as the internal rate of return remained below 29.8%. The shortest payback time was 5 years with discount rate of 5%. The price of fuel ethanol and food waste treatment fee were the most important variables for the economic performance of the plant by sensitivity analysis. This work could provide the basic knowledge for techno-economic analysis of food waste treatment and promote the industrial production of fuel ethanol.