Process integration for ethanol production from corn and corn stover as mixed substrates

A critical assessment on scalable technologies using high solids loadings in lignocellulose biorefinery: challenges and solutions

The pretreatment and the enzymatic saccharification are the key steps in the extraction of fermentable sugars for further valorization of lignocellulosic biomass (LCB) to biofuels and value-added products via biochemical and/or chemical conversion routes. Due to low density and high-water absorption capacity of LCB, the large volume of water is required for its processing. Integration of pretreatment, saccharification, and co-fermentation has succeeded and well-reported in the literature. However, there are only few reports on extraction of fermentable sugars from LCB with high biomass loading (>10% Total solids-TS) feasible to industrial reality. Furthermore, the development of enzymatic cocktails can overcome technology hurdles with high biomass loading. Hence, a better understanding of constraints involved in the development of technology with high biomass loading can result in an economical and efficient yield of fermentable sugars for the production of biofuels and bio-chemicals with viable titer, rate, and yield (TRY) at industrial scale. The present review aims to provide a critical assessment on the production of fermentable sugars from lignocelluloses with high solid biomass loading. The impact of inhibitors produced during both pretreatment and saccharification has been elucidated. Moreover, the limitations imposed by high solid loading on efficient mass transfer during saccharification process have been elaborated.

Utilization of lignocellulosic biomass by glycerol organosolv pretreatment for biobutanol production integrated with bioconversion of residual glycerol into value-added products

Glycerol organosolv pretreatment (GOP) is considered an efficient method to deconstruct lignocellulose for producing fermentable sugars. Herein, the liquid fraction containing glycerol after GOP was utilized for recycled pretreatment of corn stover (CS) for four cycles. Enzymatic yield of glucose after recycled pretreatment was enhanced by 2.4-3.5 folds compared with untreated CS. Meanwhile, residual glycerol was used as carbon source for cultivation of Pichia pastoris to obtain high cell-density, and a final titer of 1.3 g/L human lysozyme was produced by P. pastoris under low temperature methanol induction strategy. Additionally, the pretreated CS was mixed with cassava as fermentable substrates for butanol production by wild-type Clostridium acetobutylicum ATCC 824. Final butanol production of 13.9 g/L was obtained from mixed substrates (25%:75% of CS/cassava) at 10% solids loading by simultaneous saccharification and fermentation. Overall, integration of residual glycerol utilization and butanol production by microbial fermentation provided an efficient strategy for biorefinery.

Enhanced fermentable sugar production in lignocellulosic biorefinery by exploring a novel corn stover and configuring high-solid pretreatment conditions

This study aimed to produce enhanced fermentable sugars from a novel stover system through the bioprocessing of its soluble sugars and insoluble carbohydrates. The pretreatment conditions were optimized for this high sugar-containing stover (HSS) to control inhibitor formation and obtain enhanced fermentable sugar concentrations. The optimum temperature, acid loading, and reaction time for the pretreatment were 155 °C, 0.5%, and 30 min, respectively, providing up to 97.15% sugar yield and 76.51 g/L total sugars at 10% solid-load. Sugar concentration further increased to 126.9 g/L at 20% solid-load, generating 3.89 g/L acetate, 0.92 g/L 5-hydroxymethyl furfural, 0.82 g/L furfural, and 3.75 g/L total phenolics as inhibitors. To determine the effects of soluble sugars in HSS on fermentable sugar yield and inhibitor formation, sugar-removed HSS was further studied under the optimum conditions. Although prior removal of sugars exhibited a reduction in inhibitor generation, it also decreased total fermentable sugar production to 115.45 g/L.

Bioethanol production from expired cookies and economic analysis for practical application

This work examined the potential of bioethanol production from expired cookies (EC) by the separate hydrolysis and fermentation process. EC was hydrolyzed by glucoamylase with different enzyme addition (3.5 U/g to 140 U/g) to produce the EC hydrolysate. The glucose concentration increased with enzyme addition from 3.5 U/g to 14 U/g and the highest glucose concentration of 21.2 g/L was obtained. The EC hydrolysate was used by Saccharomyces cerevisiae for bioethanol production. The optimal ethanol production obtained from this study was 40.1 g/L in term of economics and efficiency. According to the mass balance, the highest ethanol yield from EC was 0.4 g/g. Techno-economic analysis of the plant with capacity of 5 tons EC/day was also assessed in this study. The total capital cost and annual operation cost were US$540400.7 and US$144543.9/y, respectively. The revenue of the plant was US$390522/y with the sales of 660 t/y ethanol and 412.5 t/y oils. The plant should feed the EC more than 1.04 t/d (334.2 t/y) to avoid the shutdown point. This is the first study to demonstrate the bioethanol production from EC and assess the economic feasibility for industrial application.

Corn Stover Pretreatment with Na2CO3 Solution from Absorption of Recovered CO2

Renewable resources such as lignocellulosic biomass are effective at producing fermentable sugars during enzymatic hydrolysis when pretreated. Optimizing pretreatment methods for delignification while maintaining sustainability and low processing costs requires innovative strategies such as reusing greenhouse gas emissions for materials processing. Corn stover, an agricultural waste residue, was pretreated with 2.2 M Na2CO3 produced from CO2 captured via absorption in a 5 M NaOH solution. Composition analysis of the pretreated corn stover exhibited higher cellulose content (40.96%) and less lignin (16.50%) than the untreated biomass. Changes in the chemical structures are visible in the FTIR-ATR spectra, particularly in the cellulose and lignin-related absorption bands. The sugar release from hydrolysis was evaluated at different time intervals and by varying two enzyme ratios of CTec2-to-HTec2 (2:1 and 3:1). Enzymatic hydrolysis produced higher and more stable glucose yields for the pretreated biomass, surpassing 90% after 24 h using the 3:1 enzyme ratio. Sugar concentrations notably increased after pretreatment and even more when using the cellulase-rich enzyme solution. The maximum glucose, xylose, and arabinose recovered were 44, 19, and 2.3 g L−1. These results demonstrate the viability of capturing CO2 and converting it into an efficient Na2CO3 pretreatment for corn stover biomass. Additional processing optimizations depend on the combination of physicochemical parameters selected.

Surfactant assisted microwave irradiation pretreatment of corncob: Effect on hydrogen production capacity, energy consumption and physiochemical structure

The combination pretreatment strategy is an effective way to intensify photo-fermentative biohydrogen production (PFHP) process. In this study, the synergistic effects of microwave irradiation and surfactants on the hydrogen production performance, energy analysis and structural characteristics was evaluated. Results revealed that hydrogen production performance was improved after microwave irradiation pretreatment (MIP) and surfactants assisted microwave irradiation pretreatment (SMIP). SMIP group had a higher cumulative hydrogen yield (CHY) of 367.87 ± 6.481 mL compared with control group (223.26 ± 4.329 mL) and MIP group (303.66 ± 3.366 mL), which was an increase of 36.01% and 64.77%, respectively. Energy evaluation analysis showed that the energy ratio of SMIP (0.49) was higher than that of MIP (0.37) in the PFHP system, therefore, SMIP can save more energy. After SMIP, the corncob lignocellulose structure was greatly damaged, which was verified by SEM, FTIR, XRD and XPS analyses.

Ethanol Production from the Mixture of Waste French Fries and Municipal Wastewater via Separate Hydrolysis and Fermentation

The potential of bioethanol generation using the mixture of waste French fries (WFF) and municipal wastewater (MWW) via separate hydrolysis and fermentation (SHF) was evaluated in this study. The effect of WFF substrate loading (SL, 10%, 16%, and 20%, w/v) on the SHF was also examined. Both glucose production and hydrolysis efficiency increased with increasing of SL from 10 to 16% and the maximum glucose yield of 0.236 g glucose/g WFF and hydrolysis efficiency of 91.9% were obtained at SL of 16%. However, the glucose production and hydrolysis efficiency decreased when the SL further increased to 20% due to the inhibition on enzyme caused by higher glucose production. The mixture hydrolysate was then used as feedstock for ethanol fermentation. The maximum ethanol production of 22.69 g/L was obtained from SL of 16%. The highest rate of glucose conversion to ethanol was 84.2%. The results demonstrated that the mixture of WFF and MWW could be used for ethanol production by the SHF.

Insights on sustainable approaches for production and applications of value added products

The increasing demand for the development of sustainable strategies to utilize and process agro-industrial residues paves new paths for exploring innovative approaches in this area. Biotechnology based microbial transformations provide efficient, low cost and sustainable approaches for the production of value added products. The use of organic rich residues opens new avenues for the production of enzymes, pigments, biofuels, bioactive compounds, biopolymers etc. with vast industrial and therapeutic applications. Innovative technologies like strain improvement, enzyme immobilization, genome editing, morphological engineering, ultrasound/supercritical fluid/pulse electric field extraction, etc. can be employed. These will be helpful in achieving significant improvement in qualitative and quantitative parameters of the finished products. The global trend for the valorisation of biowaste has boosted the commercialization of these products which has transformed the markets by providing new investment opportunities. The upstream processing of raw materials using microbes poses a limitation in terms of product development and recovery which can be overcome by modifying the bioreactor design, physiological parameters or employing alternate technologies which will be discussed in this review. The other problems related to the processes include product stability, industrial applicability and cost competitiveness which needs to be addressed. This review comprehensively discusses the recent progress, avenues and challenges in the approaches aimed at valorisation of agro-industrial wastes along with possible opportunities in the bioeconomy.

Advances in pretreatment of lignocellulosic biomass for bioenergy production: Challenges and perspectives

As a clean and renewable energy, bioenergy is one of the most promising alternatives to fossil fuels. Lignocellulose possesses great potential for bioenergy production, but the recalcitrant and heterogeneous structure limits its application. Pretreatment technology offers an effective solution to fractionate the main components of the lignocellulose and uncover the available cellulose. The obtained feedstock can be applied to bioconversion into energy, e.g., bioethanol, biogas, biohydrogen, etc. Here, the current state of lignocellulose pretreatment technologies was comprehensively reviewed, the advances in bioenergy production from pretreated lignocellulose was described, with particular attention to key challenges involved. Several new strategies for overcoming pretreatment barriers to realize highly efficient lignocellulose bioconversion were highlighted. The insights given in this review will facilitate further development on lignocellulosic bioenergy production, towards addressing the global energy crisis and climate change related to the use of fossil fuels.

Minimizing water consumption for sugar and lignin recovery via the integration of acid and alkali pretreated biomass and their mixed filtrate without post-washing

Excessive post-washing of pretreated biomass leads to huge water consumption and chemical loss. To address this issue, parallel HOAc and NaOH pretreatments of biomass followed by integration of their biomass and filtrate were investigated. Pretreatment effectiveness including morphology, crystallinity, and component recovery, were elucidated. Results showed that HOAc and NaOH in the mixed filtrate were neutralized to achieve a pH of around 4.80 prompting the alkali lignin precipitation. Lignin (46.01 and 48.38 g/kg-biomass for hemp and poplar, respectively) exhibiting comparable FTIR characteristics with the commercial alkali lignin was recovered. Compared to sodium acetate buffer as a control, integrating HOAc and NaOH pretreated biomass and their mixed filtrate for enzymatic hydrolysis boosted total sugar concentration (hemp: 42.90 vs. 38.27 g/L; poplar: 43.18 vs. 38.76 g/L) without compromising glucose yield (hemp: 70.86 vs. 70.69%; poplar: 66.48 vs. 69.48%) but improving xylose yield (hemp: 60.10 vs. 35.92%; poplar: 56.90 vs. 29.39%).

Conversion of Lignocellulose for Bioethanol Production, Applied in Bio-Polyethylene Terephthalate

The increasing demand for petroleum-based polyethylene terephthalate (PET) grows population impacts daily. A greener and more sustainable raw material, lignocellulose, is a promising replacement of petroleum-based raw materials to convert into bio-PET. This paper reviews the recent development of lignocellulose conversion into bio-PET through bioethanol reaction pathways. This review addresses lignocellulose properties, bioethanol production processes, separation processes of bioethanol, and the production of bio-terephthalic acid and bio-polyethylene terephthalate. The article also discusses the current industries that manufacture alcohol-based raw materials for bio-PET or bio-PET products. In the future, the production of bio-PET from biomass will increase due to the scarcity of petroleum-based raw materials.

Advances in Valorization of Lignocellulosic Biomass towards Energy Generation

The booming demand for energy across the world, especially for petroleum-based fuels, has led to the search for a long-term solution as a perfect source of sustainable energy. Lignocellulosic biomass resolves this obstacle as it is a readily available, inexpensive, and renewable fuel source that fulfills the criteria of sustainability. Valorization of lignocellulosic biomass and its components into value-added products maximizes the energy output and promotes the approach of lignocellulosic biorefinery. However, disruption of the recalcitrant structure of lignocellulosic biomass (LCB) via pretreatment technologies is costly and power-/heat-consuming. Therefore, devising an effective pretreatment method is a challenge. Likewise, the thermochemical and biological lignocellulosic conversion poses problems of efficiency, operational costs, and energy consumption. The advent of integrated technologies would probably resolve this problem. However, it is yet to be explored how to make it applicable at a commercial scale. This article will concisely review basic concepts of lignocellulosic composition and the routes opted by them to produce bioenergy. Moreover, it will also discuss the pros and cons of the pretreatment and conversion methods of lignocellulosic biomass. This critical analysis will bring to light the solutions for efficient and cost-effective conversion of lignocellulosic biomass that would pave the way for the development of sustainable energy systems.

Simulation of Mixing Intensity Profile for Bioethanol Production via Two-Step Fermentation in an Unbaffled Agitator Reactor

Bioethanol synthesis techniques have been studied intensively due to the energy crisis and various environmental concerns. A two-step bioethanol production process was carried out multiple times in an unbaffled agitator tank. The parameters varied, including the fermentation temperature, the pH level, the amount of yeast, and the impeller type. Then, a simulation was used to obtain an image of the agitation behavior inside the agitator tank to compare the velocity profile of each type of impeller design. The impeller with eight blades was found to produce the highest flow velocity: 0.28 m/s. The highest concentration of bioethanol generated from the fermentation was 34 g/L, which was produced by using an eight-blade impeller at 30 °C, a pH level of 5, an agitation speed of 70 rpm, and 2 wt % yeast. The two-blade impeller produced the lowest bioethanol concentration, 18 g/L, under the same conditions. Ethanol concentration was found to peak at 40 °C and a pH level of 5. The geometry of the impeller, the fermentation temperature, and the pH level were each found to have a significant effect on the resulting bioethanol concentration according to the results of an ANOVA test. The amount of yeast had no effect on the fermentation reaction. Finally, the results demonstrated the possibility of using computational fluid dynamic modeling to determine the impeller’s behavior for the development of the bioethanol fermentation process. The simulation and experimental results from this research support the scaling up of a bioethanol production facility.

Simultaneous nitrogen fixation and ethanol production by Zymomonas mobilis

This work reports on production of ethanol with simultaneous fixing of nitrogen (N₂) using the anaerobic bacterium Zymomonas mobilis DSM 473. A batch fermentation with an initial glucose concentration of 50 g L^-1, an initial pH of ∼5.5, an inoculum size of 10% by volume and a N₂ feeding rate of 50 mL min^-1 without mechanical agitation was found to provide the highest ethanol productivity (0.401 g L^-1 h^-1). Ethanol yield on glucose exceeded 97% of the theoretical maximum. The nitrogen content of the microbial biomass was 10.4% w/w at 65 h and all of it was derived by fixation of dinitrogen. Repeated-batch fermentations were investigated for ethanol production using simultaneous nitrogen fixation. A 2-cycle repeated-batch fermentation lasting 71 h gave a maximum ethanol yield on glucose of 0.475 g g^-1 and an ethanol productivity of 0.675 g L^-1 h^-1. The yield (0.415 g g^-1) and productivity (0.638 g L^-1 h^-1) were reduced in a 3-cycle repeated batch operation lasting 94 h. The need to fix nitrogen did not reduce the final achievable ethanol concentration, or the ethanol yield on glucose, relative to fermentations provided with fixed nitrogen, but did reduce the ethanol productivity by ∼82% because less cell mass was produced.

Application of industrial amylolytic yeast strains for the production of bioethanol from broken rice

Amylolytic Saccharomyces cerevisiae derivatives of Ethanol Red™ Version 1 (ER T12) and M2n (M2n T1) were assessed through enzyme assays, hydrolysis trials, electron microscopy and fermentation studies using broken rice. The heterologous enzymes hydrolysed broken rice at a similar rate compared to commercial granular starch-hydrolysing enzyme cocktail. During the fermentation of 20% dw/v broken rice, the amylolytic strains converted rice starch to ethanol in a single step and yielded high ethanol titers. The best-performing strain (ER T12) produced 93% of the theoretical ethanol yield after 96 h of consolidated bioprocessing (CBP) fermentation at 32 °C. Furthermore, the addition of commercial enzyme cocktail (10% of the recommended dosage) in combination with ER T12 did not significantly improve the maximum ethanol concentration, confirming the superior ability of ER T12 to hydrolyse raw starch. The ER T12 strain was therefore identified as an ideal candidate for the CBP of starch-rich waste streams.

On the evaluation of different saccharification schemes for enhanced bioethanol production from potato peels waste via a newly isolated yeast strain of Wickerhamomyces anomalus

The present study focuses on the exploration of the potential use of potato peels waste (PPW) as feedstock for bioethanol production, using a newly isolated yeast strain, Wickerhamomyces anomalus, via different saccharification and fermentation schemes. The saccharification of PPW was performed via thermal and chemical (acid, alkali) pretreatment, as well as via enzymatic hydrolysis through the use of commercial enzymes (cellulase and amylase) or enzymes produced at lab scale (alpha-amylase from Bacillus sp. Gb67), either separately or in mixtures. The results indicated that the enzymatic treatment by commercial enzymes led to a higher saccharification efficiency (72.38%) and ethanol yield (0.49 g/g_{consumed sugars}) corresponding to 96% of the maximum theoretical. In addition, acid pretreatment was found to be beneficial for the process, leading also to high hydrolysis and ethanol yields, indicating that PPW is a very promising feedstock for bio-ethanol production by W. anomalus under different process schemes.