Pretreatment Of Lignocellulosic Biomass Research Articles

A review of nanotechnology in enzyme cascade to address challenges in pre-treating biomass.

Nanotechnology has become a revolutionary technique for improving the preliminary treatment of lignocellulosic biomass in the production of biofuels. Traditional methods of pre-treatment have encountered difficulties in effectively degrading the intricate lignocellulosic composition, thereby impeding the conversion of biomass into fermentable sugars. Nanotechnology has enabled the development of enzyme cascade processes that present a potential solution for addressing the limitations. The focus of this review article is to delve into the utilization of nanotechnology in the pretreatment of lignocellulosic biomass through enzyme cascade processes. The review commences with an analysis of the composition and structure of lignocellulosic biomass, followed by a discussion on the drawbacks associated with conventional pre-treatment techniques. The subsequent analysis explores the importance of efficient pre-treatment methods in the context of biofuel production. We thoroughly investigate the utilization of nanotechnology in the pre-treatment of enzyme cascades across three distinct sections. Nanomaterials for enzyme immobilization, enhanced enzyme stability and activity through nanotechnology, and nanocarriers for controlled enzyme delivery. Moreover, the techniques used to analyse nanomaterials and the interactions between enzymes and nanomaterials are introduced. This review emphasizes the significance of comprehending the mechanisms underlying the synergy between nanotechnology and enzymes establishing sustainable and environmentally friendly nanotechnology applications.

Enhancing biogas production through photocatalytic pretreatment of rice straw co-digested with cow dung and food waste using a novel g-C3N4/SiO2/bentonite catalyst

This study investigates the application of a novel composite photocatalyst, g-C3N4/SiO2/ Bentonite, for rice straw pretreatment, aiming to enhance biogas production in anaerobic digestion. The photocatalytic pretreatment disrupts rice straw's lignin and hemicellulose structures, reducing silica content for improved microbial degradation. Five 2 L anaerobic digesters were employed with rice straw as the substrate and co-digestion materials, including cow dung and food waste. Rice straw treated with the g-C3N4/7.5% SiO2/5% Bentonite catalyst exhibited a remarkable 37% increase in methane yield compared to untreated rice straw. This photocatalytic process led to a 31% increase in cellulose content and a 30% reduction in lignin after 6 hours of pretreatment. Simultaneously, silica content in the rice straw decreased to 6.4% after 6 hours, resulting in a 48% increase in the carbon proportion. These findings underscore the potential of integrated photocatalysts for significantly enhancing biogas production efficiency through the pretreatment of lignocellulosic biomass.

Tuning Structural Characteristics of Corn Stover Through Ammonium and Sodium Sulfite (ASS) Pretreatment for Enhanced Enzymatic Hydrolysis.

The ammonia fiber expansion (AFEX) pretreatment of lignocellulosic biomass offers a significant advantage in terms of obtaining high glucan conversion, with the added benefit of ammonia being fully recyclable. However, despite the high efficiency of AFEX in pretreating lignocellulose, relatively high enzyme loading is still required for effective cellulose conversions. In this study, we have updated the AFEX pretreatment method; ammonia and sodium sulfite (ASS) can be used to produce a more digestible substrate. The results demonstrate that ASS-pretreated corn stover (CS) yields a higher fermentable sugar yield compared with AFEX pretreatment, even at lower enzyme loadings. Specifically, at an enzyme loading of 12 mg protein/g glucan, ASS-CS achieved 88.8% glucose and 80.6% xylose yield. Characterization analysis reveals that lignin underwent sulfonation during ASS pretreatment. This modification results in a more negative zeta potential for ASS-CS, indicating a reduction in nonproductive adsorption between lignin and cellulase through increased electrostatic repulsion.

Deletion of yghZ in Escherichia coli promotes growth in presence of furfural with xylose as carbon source.

Thermo-acidic pretreatment of lignocellulosic biomass is required to make it amenable to microbial metabolism and results in generation of furfural due to breakdown of pentose sugars. Furfural is toxic to microbial metabolism and results in reduced microbial productivity and increased production costs. This study asks if deletion of yghZ gene which encodes a NADPH-dependent aldehyde reductase enzyme results in improved furfural tolerance in Escherichia coli host. The ∆yghZ strain-SSK201-was tested for tolerance to furfural in presence of 5% xylose as a carbon source in AM1 minimal medium. At 96h and in presence of 1.0g/L furfural, the culture harboring strain SSK201 displayed 4.5-fold higher biomass, 2-fold lower furfural concentration and 15.75-fold higher specific growth rate (µ) as compared to the parent strain SSK42. The furfural tolerance advantage of SSK201 was retained when the carbon source was switched to glucose in AM1 medium and was lost in rich LB medium. The findings have potential to be scaled up to a hydrolysate culture medium, which contains furan inhibitors and lack nutritionally rich components, under bioreactor cultivation and observe growth advantage of the ∆yghZ host. It harbors potential to generate robust industrial strains which can convert lignocellulosic carbon into metabolites of interest in a cost-efficient manner.

Autohydrolysis of sugarcane bagasse with water reuse: Impacts on residues’ composition and enzymatic hydrolysis

This work presents a new sequential approach to the sugarcane bagasse autohydrolysis process in a way that the liquor from the previous reaction was reused in the next one, and the makeup water for the next batch was used to wash the solid fraction before being added to the liquor in the next batch. This approach was suggested first as a way of reducing the water usage in the process, and second as a way of concentrating the liquor in any interesting component, working with the possibility of losing efficiency towards the glucose production through a cellulose loss to the liquor or enzymatic efficiency loss from a higher inhibitor concentration. Two sets of five sequential batches were performed: one washing the solids with the makeup water prior to the enzymatic step (Set 2), and the other one without the washing step (Set 1), looking forward to the effects of the water reuse over the glucose production and the liquor composition. Autohydrolysis pretreatment removed most of the hemicellulose (∼94 %), with liquor recycling improving its removal until the third batch and stabilizing after that. Although the washing step showed little impact on the composition of the solids, it was determinant to the success of the enzymatic hydrolysis, since it was possible to maintain the cellulose to glucose yield around 53% throughout the batches. There was a 64 % reduction in the water used in the sequential reactions without interfering in the glucose production, which indicates that the proposed strategy could be successfully used to reduce costs and environmental impacts associated with the pretreatment of lignocellulosic biomass.

Combined leaching and steam explosion pretreatment of lignocellulosic biomass for high quality feedstock for thermochemical applications

A novel pretreatment approach was developed in the present study to simultaneously reduce the content of inorganic troubling elements (TEs) and improve biomass energy density, i.e., combined leaching and steam explosion (SE) pretreatment with mechanical pressing. Three different high-ash-containing biomass feedstocks were studied – wheat straw (WS), spruce bark (SB), and empty fruit bunches of oil palm (EFB). Before studying the combined pretreatment, the impact of individual pretreatment was determined in-depth on biomass composition and ash-transformation behaviour. In leaching pretreatment, the effect of leaching with steam explosion condensate (SEC), dilute acetic acid and water was studied comprehensively. The solid (raw and treated) and liquid samples (leachate, SEC, hydrolysate) were characterized for a detailed comparative analysis. The ash-fusion and −transformation behaviour of raw and pretreated biomass was studied in-depth using advanced multicomponent thermodynamic equilibrium modelling (TEM) and push-rod dilatometry. After combined pretreatment, a considerably high reduction in TEs content was noted: 82–98 % K, 93–99 % Na, 80–99 % Cl, 34–90 % S, 3–77 % Mg, ash 43–63 %, 26–67 % P, and 19–63 % Ca. Simultaneously, heating values of all three feedstocks increased by 1.3–2.3 MJ/kg, reaching up to 20–22 MJ/kg. TEM results reveal that much lesser amounts of molten slag and volatile inorganic compounds were formed in pretreated samples compared to raw and SE biomass, such as K2Si5MgO12, KCl, KPMgO4, K2Si2O5, CaSiO3, and MgSiO3 in WS; Na2CO3, K2CO3, K2CaC2O6, KPMgO4, and CaCO3 in SB. Due to higher energy density and lower propensity towards ash-related issues, combined pretreated WS and SB have a high potential to be used in large-scale thermochemical applications.

Multi enzyme production from mixed untreated agricultural residues applied in enzymatic saccharification of lignocellulosic biomass for biofuel

Lignocellulose recalcitrance essentially dictates high cost and low efficiency of its enzymatic saccharification. The complex lignocellulosic structure is a major obstacle to enzymatic saccharification and green ionic liquid pretreatment methods face difficulty of water washing prior enzymatic hydrolysis. Ionic liquid tolerant lignocellulolytic enzymes overcome the inhibition of enzymes during enzymatic saccharification and eliminated water washing step after pretreatment of lignocellulosic biomass. The cell wall composition cellulose, hemicellulose, and lignin, three main wall polymers of various agricultural residues and food waste lignocellulose substrates also affected the enzyme activities secreted by the B. subtilis strain. This study explores the potential of the halophilic, alkalophilic, and ionic liquid (IL)-tolerant strain Bacillus subtilis BC-001 for the simultaneous production of hydrolytic enzymes essential for lignocellulosic bio-refinery processes. BC-001 produced cellulase, amylase, xylanase, pectinase and protease are 70.41, 87.14, 65.50, 122.55 and 66.48 U/mL, respectively under optimized fermentation conditions. Cellulase produced by BC-001 retained more than 80% activity after 72 hours in 20% w/w of different ILs tested and enzymes retained more than 68% activities after 12 h in 50% w/w ILs. Employing such IL-stable cellulase, enzymatic saccharification is conducted without water washing on rice straw (RS) that has been pretreated with various ILs, including 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, and choline chloride. This research is novel as the study marks the first instance of multi-hydrolytic enzyme production from a novel alkalophilic, halophilic, thermophilic, and IL-tolerant bacterial strain using a mixture of untreated agricultural residues.

The optimization of sodium hydroxide (NaOH) pre-treatment for reducing sugar production from rice husk using response surface methodology (RSM)

Lignocellulosic biomass is an abundant renewable resource which amounts to 1.3 billion tonnes per year and can be used in a variety of sustainable applications. It is primarily made up of tightly bound cellulose, hemicellulose, and lignin. However, hemicellulose dissolution and delignification pose significant challenges to the utilisation of reducing sugar. To solve this issue, alkaline pretreatment was utilised. The aim of lignocellulosic biomass pretreatment is to break down the complex structure of the biomass and provide better access to the components that can be converted into useful reducing sugar. Response Surface Methodology (RSM) was used to identify the optimal values for the factors influencing the pretreatment. The optimisation parameters were sodium hydroxide concentration (1 – 4 % w/v), pretreatment time (15 – 60 minutes), and solid loading (6 – 16% w/v). Rice husk, which was used as biomass, was hydrolysed enzymatically to produce reduced sugar. The optimum conditions for producing the highest reducing sugar of 15.18 mg/mL from rice husk were 1.67% w/v sodium hydroxide pretreatment, 59.44 minutes of pretreatment time, and 7.67% w/v solid loading. As a result, less alkaline reagents can be used with a longer pretreatment time, thus lowering the cost of pretreatment. Therefore, this shows that RSM was one of the best methods to replace the conventional technique for optimising the parameters of rice husk alkaline pretreatment for reducing sugar production.

Comprehensive understanding of co-producing fermentable sugar, furfural, and xylo-oligosaccharides through the pretreatment with CTAB-based deep eutectic solvent containing Brønsted and Lewis acid

The deep eutectic solvents (DESs) with additional functionalities synthesized using the cationic surfactant cetyltrimethylammonium bromide (CTAB) have gained attention due to their remarkable enzymatic enhancement capability. By combining CTAB, lactic acid, and FeCl3, a DES containing both Brønsted and Lewis acids was synthesized and the pretreatment parameters were optimized using response surface methodology. The results demonstrated the selective and efficient delignification (83.2 %) and xylan removal (76.3 %) from canola straw by CTAB:LA:Fe3+, resulting in an increased saccharification efficiency of 81.8 %. Besides, abundant furfural (3.36 g/L) and xylo-oligosaccharides (3.41 g/L) were co-produced during pretreatment, providing comprehensive insights into the efficient co-production of fermentable sugars, furfural, and xylo-oligosaccharides. A thorough analysis of mass balance and energy flow was conducted to evaluate the entire process. Then, molecular dynamics (MD) simulations and quantum chemical calculations were performed on lignocellulosic biomass models and elucidate the interactions between the biomass and CTAB:LA:Fe3+ at the molecular level through the independent gradient model (IGM), thus explaining the high removal efficiency of hemicellulose and lignin. Furthermore, the physicochemical properties of the DESs were investigated, and molecular-level insights into the mechanism of CTAB:LA:Fe3+ pretreatment of lignocellulosic biomass were proposed in conjunction with biomass characterization such as FT-IR and CLSM, as well as MD simulations.

Novel Advanced Oxidation Processes (AOPs) as Lignocellulosic Biomass Pretreatment Approaches and Their Sustainability Assessment: A Review

Novel Advanced Oxidation Processes (AOPs) as Lignocellulosic Biomass Pretreatment Approaches and Their Sustainability Assessment: A Review

Improving furfural tolerance in a xylose-fermenting yeast Spathaspora passalidarum CMUWF1–2 via adaptive laboratory evolution

BackgroundSpathaspora passalidarum is a yeast with the highly effective capability of fermenting several monosaccharides in lignocellulosic hydrolysates, especially xylose. However, this yeast was shown to be sensitive to furfural released during pretreatment and hydrolysis processes of lignocellulose biomass. We aimed to improve furfural tolerance in a previously isolated S. passalidarum CMUWF1−2, which presented thermotolerance and no detectable glucose repression, via adaptive laboratory evolution (ALE).ResultsAn adapted strain, AF2.5, was obtained from 17 sequential transfers of CMUWF1−2 in YPD broth with gradually increasing furfural concentration. Strain AF2.5 could tolerate higher concentrations of furfural, ethanol and 5-hydroxymethyl furfuraldehyde (HMF) compared with CMUWF1−2 while maintaining the ability to utilize glucose and other sugars simultaneously. Notably, the lag phase of AF2.5 was 2 times shorter than that of CMUWF1−2 in the presence of 2.0 g/l furfural, which allowed the highest ethanol titers to be reached in a shorter period. To investigate more in-depth effects of furfural, intracellular reactive oxygen species (ROS) accumulation was observed and, in the presence of 2.0 g/l furfural, AF2.5 exhibited 3.41 times less ROS accumulation than CMUWF1−2 consistent with the result from nuclear chromatins diffusion, which the cells number of AF2.5 with diffuse chromatins was also 1.41 and 1.24 times less than CMUWF1−2 at 24 and 36 h, respectively.ConclusionsAn enhanced furfural tolerant strain of S. passalidarum was achieved via ALE techniques, which shows faster and higher ethanol productivity than that of the wild type. Not only furfural tolerance but also ethanol and HMF tolerances were improved.

Innovative Power Generation Technologies for Improved Household Energy Delivery and Sustainable Future: Classical Solutions from ENEA Research Centre, Trisaia Italy

The present communication is focused predominantly on important R&D solutions relevant to renewable energy technologies covering the following: (i) Innovative heat transfer fluid and thermal storage technology based on a molten salt mixture developed by ENEA for large-scale heat storage. The system uses a parabolic trough collector, compared with diathermic oil, which allows higher operating temperature, resulting in significant benefits to the plant’s operation, safety and the environment. (ii) The world’s first solar disk powered by air micro turbine developed by ENEA. (iii) An innovative steam-explosion prototype plant installed at ENEA for the pre-treatment of lignocellulosic biomass and the fractionation of bio components to generate ethanol from lignocellulosic material using hemicellulose and lignin. (iv) The production of hydrogen-enriched biogas using steam as the gasification agent, which helps in obtaining nearly nitrogen-free product gas and with a high calorific value of around 12 MJ/Nm3 dry gas and a high percentage of hydrogen (up to 55%) while using steam as the gasifying agent in the presence of a catalyst. (v) A rotary kiln plant, with the main purpose being to develop and optimize a thermo-chemical process to convert used rubber tyres so as to recover material and energy, as well as other solid products, with high value-added “Activated carbon” and synthesis gas.

Potential of ionic liquids as emerging green solvent for the pretreatment of lignocellulosic biomass.

Lignocellulosic biomass is available in abundance as a renewable resource, but the major portion of it is often discarded as waste without utilizing its immense potential as an alternative renewable energy resource. To overcome recalcitrance of lignocellulosic biomass, various pretreatment methods are applied to it, so that the complex and rigid polymeric structure can be broken down into fractions susceptible for enzymatic hydrolysis. Effective and efficient biomass processing is the goal of pretreatment methods, but none of the explored pretreatment methods are versatile enough to fulfil the requirement of biomass processing with greater flexibility in terms of operational cost and desired output efficiency. Deployment of green solvents such as ionic liquids for the pretreatment of lignocellulosic biomass has been a topic of discussion amongst the scientific community in recent times. The presented work provides a detailed overview on the deployment of ionic liquid for the pretreatment of lignocellulosic biomass coupled with a brief discussion on other pretreatments methods. The recyclability and reusability along with other unique properties makes an ionic liquid pretreatment different from the other traditional pretreatment methods. Also, this study explores diverse critical parameters that governs the dissolution process of biomass. Hazardous properties of ionic liquids have also been explored. Future perspective and recommendations have been given for an efficient, effective, and eco-friendly deployment of ionic liquid in biomass pretreatment process.

The pretreatment and enzymatic hydrolysis behaviors of lignocellulosic biomass (oak and larch) based on structural changes in its lignin-carbohydrate complex

This study investigated the structural changes in oak and larch lignin-carbohydrate complexes (LCCs) during hydrothermal treatment and enzymatic hydrolysis. Hydrothermal treatment caused hemicellulose degradation (degradation rate at 170 ℃: larch 19.40%; oak, 22.26%). The LCC1 (glucan-lignin) fraction was the highest in the raw material of both biomasses. The LCC3 (xylan-lignin) and LCC2 (glucomannan-lignin) fractions were high in oak and larch, respectively; these fractions decreased as the hydrothermal treatment temperature increased (owing to hemicellulose degradation). Both biomasses had phenyl glycoside, benzyl ether (BE), and γ-ester (Est) linkages. The BE and Est linkages decreased as the hydrothermal treatment temperature increased; the Est linkages decrease was more significantly in oak than in larch. The efficiency of enzymatic hydrolysis was higher in oak than that in larch and increased as the hydrothermal treatment temperature increased. Furthermore, enzyme adsorption on the LCC1 sensor was higher in oak than in larch. The chemical compositions and LCC linkages of the biomass were changed by the hydrothermal treatment, which affected the efficiency of enzymatic hydrolysis. Moreover, the efficiency of enzymatic hydrolysis was higher for oak than for larch because of the difference hemicellulose and cellulose contents and LCC linkages.

Tailoring a cellulolytic enzyme cocktail for efficient hydrolysis of mildly pretreated lignocellulosic biomass

Commercially available cellulase cocktails frequently demonstrate high efficiency in hydrolyzing easily digestible pretreated biomass, which often lacks hemicellulose and/or lignin fractions. However, the challenge arises with enzymatic hydrolysis of mildly pretreated lignocellulosic biomasses, which contain cellulose, hemicellulose and lignin in high proportions. This study aimed to address this question by evaluating the supplementation of a commercial cellulolytic cocktail with accessory hemicellulases and two additives (H2O2 and Tween® 80). Statistical optimization methods were employed to enhance the release of glucose and xylose from mildly pretreated sugarcane bagasse. The optimized supplement composition resulted in the production of 304 and 124 mg g−1 DM of glucose and xylose, respectively, significantly increasing glucose release by 84% and xylose release by 94% compared to using only the cellulolytic cocktail. This enhancement might be attributed to a coordinated hemicellulases action degrading hemicellulose, creating more space for cellulase activity, potentially boosted by the presence of H2O2 and Tween® 80. However, the addition of different concentrations of H2O2 in combination with hemicellulase and Tween® 80 did not result a significant difference on sugar release, which could be attributed to the limited range of concentrations studied (5 to 65 µM). The results obtained in this study using the mix of three supplements were also compared to the addition of only hemicellulase and only Tween® 80 to the cellulolytic cocktail. A significant increase in glucose release of 39% and 41%, respectively, was observed when using the optimized combination. For xylose, the increase was 38% and 41%, respectively. This study underscores the substantial potential in optimizing enzyme cocktails for the hydrolysis of mildly pretreated lignocellulosic biomass by using enzymes and additive combinations tailored to the specific biomass composition.

Isolation of delignifying bacteria and optimization of microbial pretreatment of biomass for bioenergy.

Microbial pretreatment of lignocellulosic biomass holds significant promise for environmentally friendly biofuel production, offering an alternative to fossil fuels. This study focused on the isolation and characterization of two novel delignifying bacteria, GIET1 and GIET2, to enhance cellulose accessibility by lignin degradation. Molecular characterization confirmed their genetic identities, providing valuable microbial resources for biofuel production. Our results revealed distinct preferences for temperature, pH, and incubation period for the two bacteria. Bacillus haynesii exhibited optimal performance under moderate conditions and shorter incubation period, making it suitable for rice straw and sugarcane bagasse pretreatment. In contrast, Paenibacillus alvei thrived at higher temperatures and slightly alkaline pH, requiring a longer incubation period ideal for corn stalk pretreatment. These strain-specific requirements highlight the importance of tailoring pretreatment conditions to specific feedstocks. Structural, chemical, and morphological analyses demonstrated that microbial pretreatment reduced the amorphous lignin, increasing cellulose crystallinity and accessibility. These findings underscore the potential of microbial pretreatment to enhance biofuel production by modifying the lignocellulosic biomass. Such environmentally friendly bioconversion processes offer sustainable and cleaner energy solutions. Further research to optimize these methods for scalability and broader application is necessary in the pursuit for more efficient and greener biofuel production.

Dual assistance of surfactants in glycerol organosolv pretreatment and enzymatic hydrolysis of lignocellulosic biomass for bioethanol production

This study investigated an innovative strategy of incorporating surfactants into alkaline-catalyzed glycerol pretreatment and enzymatic hydrolysis to improve lignocellulosic biomass (LCB) conversion efficiency. Results revealed that adding 40 mg/g PEG 4000 to the pretreatment at 195 °C obtained the highest glucose yield (84.6%). This yield was comparable to that achieved without surfactants at a higher temperature (240 °C), indicating a reduction of 18.8% in the required heat input. Subsequently, Triton X-100 addition during enzymatic hydrolysis of PEG 4000-assisted pretreated substrate increased glucose yields to 92.1% at 6 FPU/g enzyme loading. High-solid fed-batch semi-simultaneous saccharification and co-fermentation using this dual surfactant strategy gave 56.4 g/L ethanol and a positive net energy gain of 1.4 MJ/kg. Significantly, dual assistance with surfactants rendered 56.3% enzyme cost savings compared to controls without surfactants. Therefore, the proposed surfactant dual-assisted promising approach opens the gateway to economically viable enzyme-mediated LCB biorefinery.

Deep eutectic solvent cocktail enhanced the pretreatment efficiency of lignocellulose

Pretreatment of lignocellulosic biomass by breaking down its complex structure is an essential step to facilitate enzymatic hydrolysis of lignocellulose and subsequent bioethanol fermentation. Herein, an eco-friendly pretreatment strategy was developed by applying deep eutectic solvent (DES) cocktail. Attributing to the synergistic effect of two DESs (e.g., betaine-glycerol and choline chloride-oxalic acid (or choline chloride-acetamide)), an impressive 89.51% digestibility for glucan and 75.43% for xylan were achieved. Characterization of pretreated corn stover showed that DES cocktail changed substrate surface structure and enlarged structure pores, which could improve the accessibility of cellulase. The pretreated corn stover was also employed in ethanol fermentation and achieved the yield of 73.35%. Recycling experiments demonstrated the potential reusability of DES cocktail in a sustainable manner towards various biomass sources. These findings highlight the effectiveness and versatility of the developed DES cocktail pretreatment method, paving the way for sustainable bioethanol production from lignocellulosic feedstocks.

Pretreatment and enzymatic hydrolysis optimization of lignocellulosic biomass for ethanol, xylitol, and phenylacetylcarbinol co-production using Candida magnoliae.

Cellulosic bioethanol production generally has a higher operating cost due to relatively expensive pretreatment strategies and low efficiency of enzymatic hydrolysis. The production of other high-value chemicals such as xylitol and phenylacetylcarbinol (PAC) is, thus, necessary to offset the cost and promote economic viability. The optimal conditions of diluted sulfuric acid pretreatment under boiling water at 95°C and subsequent enzymatic hydrolysis steps for sugarcane bagasse (SCB), rice straw (RS), and corn cob (CC) were optimized using the response surface methodology via a central composite design to simplify the process on the large-scale production. The optimal pretreatment conditions (diluted sulfuric acid concentration (% w/v), treatment time (min)) for SCB (3.36, 113), RS (3.77, 109), and CC (3.89, 112) and the optimal enzymatic hydrolysis conditions (pretreated solid concentration (% w/v), hydrolysis time (h)) for SCB (12.1, 93), RS (10.9, 61), and CC (12.0, 90) were achieved. CC xylose-rich and CC glucose-rich hydrolysates obtained from the respective optimal condition of pretreatment and enzymatic hydrolysis steps were used for xylitol and ethanol production. The statistically significant highest (p ≤ 0.05) xylitol and ethanol yields were 65% ± 1% and 86% ± 2% using Candida magnoliae TISTR 5664. C. magnoliae could statistically significantly degrade (p ≤ 0.05) the inhibitors previously formed during the pretreatment step, including up to 97% w/w hydroxymethylfurfural, 76% w/w furfural, and completely degraded acetic acid during the xylitol production. This study was the first report using the mixed whole cells harvested from xylitol and ethanol production as a biocatalyst in PAC biotransformation under a two-phase emulsion system (vegetable oil/1M phosphate (Pi) buffer). PAC concentration could be improved by 2-fold compared to a single-phase emulsion system using only 1M Pi buffer.

Perspectives and Progress in Bioethanol Processing and Social Economic Impacts

The liquid biofuel bioethanol is widely produced worldwide via fermenting sugars extracted from a variety of raw materials, including lignocellulose biomass, one of the world’s most abundant renewable resources. Due to its recalcitrant character, lignocellulose is usually pretreated by mechanical, chemical, and biological methods to maximize sugar recovery. Pretreated lignocellulose biomass undergoes a fermentation process performed sequentially or simultaneously to saccharification. The different fermentation strategies (e.g., separate or simultaneous hydrolysis and fermentation or co-fermentation) and conditions (e.g., inoculum type load, agitation, temperature, and pH) affect ethanol yield. Genetic modification of the inoculum has been focused recently to improve ethanol tolerance and as well as to use different sugars to enhance the performance of the microorganisms involved in fermentation. Nonetheless, these improvements result in a substantial increase in costs and have certain environmental costs. This review offers an overview of advancements in bioethanol production, with a primary focus on lignocellulosic feedstock, while also considering other feedstocks. Furthermore, it provides insights into the economic, social, and environmental impacts associated with bioethanol production.