Improvement of ethanol and biogas production from sugarcane bagasse using sodium alkaline pretreatments

Thermodynamic modeling of freeze pretreatment in the destruction of rice straw structure combined with alkaline-hydrothermal method for enzymatic hydrolysis

Freeze pretreatment combined with alkaline-hydrothermal method of rice straw for enzymatic hydrolysis was studied. Crystallization stress in the rice stem pores caused by water freezing at -20- -40 °C was modeled to illustrate the destruction mechanism. The stress was calculated as 22.5-38.3 MPa that were higher than the tensile yield stress of untreated stems (3.0 MPa), indicating ice formation damaging pore structure. After freeze at -20 °C, rice straw was further hydrothermally treated at 190 °C with 0.4 M Na2CO3, achieving 72.0 % lignin removal and 97.2 % cellulose recovery. Glucose yield rose to 91.1 % by 4.3 times after 24 h hydrolysis at 10 FPU loading of Cellic®CTec2 cellulase. The specific surface area of rice straw was 2.6 m2/g increased by 1.2 times after freeze. Freeze combined with alkaline-hydrothermal treatment is a green and energy-efficient method for improving enzymatic hydrolysis.

Biogas from lignocellulosic feedstock: current status and challenges

The organic wastes and residues generated from agricultural, industrial, and domestic activities have the potential to be converted to bioenergy. One such energy is biogas, which has already been included in rural areas as an alternative cooking energy source and agricultural activities. It is produced via anaerobic digestion of a wide range of organic nutrient sources and is an essential renewable energy source. The factors influencing biogas yield, i.e., the various substrate, their characteristics, pretreatment methods involved, different microbial types, sources, and inoculum properties, are analyzed. Furthermore, the optimization of these parameters, along with fermentation media optimization, such as optimum pH, temperature, and anaerobic digestion strategies, is discussed. Novel approaches of bioaugmentation, co-digestion, phase separation, co-supplementation, nanotechnology, and biorefinery approach have also been explored for biogas production. Finally, the current challenges and prospects of the process are discussed in the review.

Extraction of lignin-containing nanocellulose fibrils from date palm waste using a green solvent

Lignin-containing nanocellulose (LNC) is a compelling alternative to traditional nanocellulose (NC), it offers enhanced yields and a reduction in the demand for toxic chemicals. This research involves the isolation of LNC from date palm waste using a green hydrolysis process and its subsequent characterization. The potential of using ionic liquids (ILs) as green solvents to isolate LNC has not yet been explored. Our findings suggest that 1-ethyl-3-methylimidazolium chloride ([Emim]Cl) can hydrolyze partially delignified and unbleached lignocellulose, achieving LNC synthesis. The obtained LNC showed a higher yield than its NC counterpart and exhibited rod-shaped fibers with nanoscale diameters and micrometer lengths, indicating a high aspect ratio. Dynamic Light Scattering (DLS) results indicate average particle sizes of 143.20 nm for NC and 282.30 nm for LNC, with a narrow particle size distribution conforming their monodisperse behavior. Thermogravimetric analysis and differential scanning calorimetry revealed high thermal stability (initial degradation temperature = 222.50 °C and glass transition temperature = 84.45°C) of LNC. Moreover, the obtained LNC fibers were crystalline (crystallinity index = 52.76 %). Their activation energy (124.95 kJ/mol) was determined using the Coats-Redfern method by employing eight solid-state diffusion models. Overall, this study motivates the use of ILs as green solvents to produce lignocellulose derivatives that are suitable for various applications.

Sustainable valorization of sugarcane residues: Efficient deconstruction strategies for fuels and chemicals production

The global climate crisis and the ongoing increase in fossil-based fuels have led to an alternative solution of using biomass for fuel production. Sugarcane bagasse (SCB) is an agricultural residue with a global production of more than 100 million metric tons and it has various applications in a biorefinery concept. This review brings forth the composition, life cycle assessment, and various pretreatments for the deconstruction techniques of SCB for the production of valuable products. The ongoing research in the production of biofuels, biogas, and electricity utilizing the bagasse was elucidated. SCB is used in the production of carboxymethyl cellulose, pigment, lactic acid, levulinic acid, and xylooligosaccharides and it has prospective in meeting the demand for global energy and environmental sustainability.

Pretreatment of milled and unchopped sugarcane bagasse with vortex based hydrodynamic cavitation for enhanced biogas production

Anaerobic digestion can potentially valorise sugarcane bagasse to biogas and fertiliser. Pretreatment is however required to overcome recalcitrance and enhance the biogas yields. Literature reporting the investigation of various biomass pretreatments often use milled biomass as substrate rather than as-received fibrous biomass. This does not establish the true influence of the pretreatment type on biogas generation. Additionally, milling energy is also ignored when calculating net energy gains from enhanced biogas yields and are thus misleading. In this work, a vortex-based hydrodynamic cavitation device was used to enhance the biomethane yields from fibrous as-received biomass for the first time. Clear justification on why milled biomass must not be used as substrates for demonstrating the effect of pretreatment on biogas production is also discussed. The net energy gain from milled hydrodynamic cavitation pre-treated bagasse can be similar to as-received bagasse only when the specific milling energy is ≤700 kWh/ton.

Sugarcane bagasse into value-added products: a review

Strategic valorization of readily available sugarcane bagasse (SB) is very important for waste management and sustainable biorefinery. Conventional SB pretreatment methods are ineffective to meet the requirement for industrial adaptation. Several past studies have highlighted different pretreatment procedures which are lacking environmentally benign characteristics and effective SB bioconversion. This article provides an in-depth review of a variety of environmentally acceptable thermochemical and biological pretreatment techniques for SB. Advancements in the conversion processes such as pyrolysis, liquefaction, gasification, cogeneration, lignin conversion, and cellulose conversion via fermentation processes are critically reviewed for the formation of an extensive array of industrially relevant products such as biofuels, bioelectricity, bioplastics, bio adsorbents, and organic acids. This article would provide comprehensive insights into several crucial aspects of thermochemical and biological conversion processes, including systematic perceptions and scientific developments for value-added products from SB valorization. Moreover, it would lead to determining efficient pretreatment and/or conversion processes for sustainable development of industrial-scale sugarcane-based biorefinery.

Opportunities in the microbial valorization of sugar industrial organic waste to biodegradable smart food packaging materials

Many petroleum-derived plastics, including food packaging materials are non-biodegradable and designed for single-use applications. Annually, around 175 Mt. of plastic enters the land and ocean ecosystems due to mismanagement and lack of techno economically feasible plastic waste recycling technologies. Renewable sourced, biodegradable polymer-based food packaging materials can reduce this environmental pollution. Sugar production from sugarcane or sugar beet generates organic waste streams that contain fermentable substrates, including sugars, acids, and aromatics. Microbial metabolism can be leveraged to funnel those molecules to platform chemicals or biopolymers to generate biodegradable food packaging materials that have active or sensing molecules embedded in biopolymer matrices. The smart package can real-time monitor food quality, assure health safety, and provide economic and environmental benefits. Active packaging materials display functional properties such as antimicrobial, antioxidant, and light or gas barrier. This article provides an overview of potential biodegradable smart/active polymer packages for food applications by valorizing sugar industry-generated organic waste. We highlight the potential microbial pathways and metabolic engineering strategies to biofunnel the waste carbon efficiently into the targeted platform chemicals such as lactic, succinate, muconate, and biopolymers, including polyhydroxyalkanoates, and bacterial cellulose. The obtained platform chemicals can be used to produce biodegradable polymers such as poly (butylene adipate-co-terephthalate) (PBAT) that could replace incumbent polyethylene and polypropylene food packaging materials. When nanomaterials are added, these polymers can be active/smart. The process can remarkably lower the greenhouse gas emission and energy used to produce food-packaging material via sugar industrial waste carbon relative to the petroleum-based production. The proposed green routes enable the valorization of sugar processing organic waste into biodegradable materials and enable the circular economy.

Anaerobic digestion of sugarcane bagasse for biogas production and digestate valorization

Sugarcane bagasse is an abundantly available agricultural waste having high potential that is still underutilized and mostly burnt as fuel. There are various processes available for bagasse utilization in improved ways and one such process is anaerobic digestion (AD) of bagasse for biogas production. The complex structure of biomass is recalcitrant to degradation and is a major hindrance for the anaerobic digestion, so different pretreatment methods are applied to deconstruct the bagasse for microbial digestion. In this review, different processes developed for the pretreatment of bagasse and their effect on biogas production have been extensively covered. Moreover, combination of pretreatment methods, co-digestion of bagasse with other waste (nitrogen rich or easily digestible) for enhanced biogas production and biomethane generation along with other value-added products has also been reviewed. The digestate contains a significant amount of organics with partial recovery of energy and products and is generated in huge amount that further creates disposal problem. Therefore, integration of digestate valorization with AD through gasification, pyrolysis, hydrothermal carbonization and use of microalgae for maximum recovery of energy and value-added products have also been evaluated. Thus, this review highlights major emerging area of research for improvement in bagasse based processes for enhanced biogas production along with digestate valorization to make the overall process economical and sustainable.

Optimization of chemical solution concentration and exposure time in the alkaline pretreatment applied to sugarcane bagasse for methane production

ABSTRACTSugarcane is the most traded crop in the world, with Brazil being the world's largest producer. Sugarcane processing generates up to 28% of sugarcane bagasse (SB) from the entire plant, with only 50% of it used for energy generation. SB is a lignocellulosic biomass that can be converted into biogas. However, the optimization of pretreatment process parameters is essential for its successful scaling up. This study evaluated the effect of mild alkaline pretreatment of SB using NaOH and KOH at concentrations of 1-10% and exposure time of 1-12 hours) on the biochemical methane potential (BMP) under mesophilic temperature. The central composite rotatable design (CCRD) was applied as statistical tool to generate optimal operating pretreatment conditions. The tests were performed in triplicates totalizing 84 batch bottles. The BMP of the untreated SB varied between 297-306 L_N CH₄ kg VS^-1 while the BMP of the pretreated samples with NaOH and KOH were 19% and 20% higher. The optimized conditions were NaOH at 7.7% and KOH at 8.3% KOH for 12 hours. However, the range indicated by the statistical design with CCRD revealed that there was no statistical difference in terms of methane yield when concentrations between 4-10% NaOH and 6-10% KOH during 12 hours were applied, when compared to the specific optimized points. The optimization of the pretreatment parameters demonstrated to be a key-factor to improve the anaerobic digestion of lignocellulosic substrates, leading to a less chemically dependent and more sustainable approach, while allowing a more profitable process.

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.

Hydrothermal pretreatment: An efficient process for improvement of biobutanol, biohydrogen, and biogas production from orange waste via a biorefinery approach

Orange waste (OW), an abundant and severe globally environmental treat, was used for biobutanol and biohydrogen production emploing acetone-butanol-ethanol (ABE) fermentation through a biorefinery process. The solvent yield from untreated OW was insufficient; thus, the substrate was subjected to hydrothermal pretreatment before hydrolysis. The pretreatment at 140 ℃ for 30 min resulted in the solid with the highest yield of hydrolysis and fermentation. Moreover, the anaerobic digestion of hydrolysis residue produced appreciable amounts of biomethane. However, the pretreatment liquor was not fermentable; thus, it was detoxified by overliming for 24 h at 30 ℃ and then fermented. Overall, this sustainable biorefinery, based on pretreatment without any additional chemical agent, hydrolysis of pretreated solids, detoxification of pretreatment liquor, ABE fermentation, and anaerobic digestion of residues, produced 42.3 g biobutanol, 33.1 g acetone, 13.4 g ethanol, 104.5 L biohydrogen, and 28.3 L biomethane per kg of OW that contained 4560 kJ energy.

Sugarcane bagasse: a biomass sufficiently applied for improving global energy, environment and economic sustainability

Sugarcane (Saccharum officinarum) bagasse (SCB) is a biomass of agricultural waste obtained from sugarcane processing that has been found in abundance globally. Due to its abundance in nature, researchers have been harnessing this biomass for numerous applications such as in energy and environmental sustainability. However, before it could be optimally utilised, it has to be pre-treated using available methods. Different pre-treatment methods were reviewed for SCB, both alkaline and alkali-acid process reveal efficient and successful approaches for obtaining higher glucose production from hydrolysis. Procedures for hydrolysis were evaluated, and results indicate that pre-treated SCB was susceptible to acid and enzymatic hydrolysis as > 80% glucose yield was obtained in both cases. The SCB could achieve a bio-ethanol (a biofuel) yield of > 0.2 g/g at optimal conditions and xylitol (a bio-product) yield at > 0.4 g/g in most cases. Thermochemical processing of SCB also gave excellent biofuel yields. The plethora of products obtained in this regard have been catalogued and elucidated extensively. As found in this study, the SCB could be used in diverse applications such as adsorbent, ion exchange resin, briquettes, ceramics, concrete, cement and polymer composites. Consequently, the SCB is a biomass with great potential to meet global energy demand and encourage environmental sustainability.

Pretreatment of lignocellulosic biomass: A review on recent advances

Depleting fossil reserves and growing energy needs have raised the demand for an alternative and clean energy source. The use of ubiquitously available lignocellulosic biomass for developing economic and eco-friendly large scale biorefinery applications has provided the much-needed impetus in this regard. The pretreatment process is a vital step for biomass transformation into added value products such as sugars, biofuels, etc. Different pretreatment approaches are employed to overcome the recalcitrance of lignocellulosic biomass and expedite its disintegration into individual components- cellulose, hemicellulose, and lignin. The conventional pretreatment methods lack sustainability and practicability for industrial scale up. The review encompasses the recent advances in selective physical and chemical pretreatment approaches such as milling, extrusion, microwave, ammonia fibre explosion, eutectic solvents etc. The study will allow a deeper understanding of these pretreatment processes and increase their scope as sustainable technologies for developing modern biorefineries.

Ethanol from rice byproduct using amylases secreted by Rhizopus microsporus var. oligosporus. Enzyme partial purification and characterization

A three-stage bioethanol bioprocess was developed. Firstly, amylases were obtained from Rhizopus microsporus var. oligosporus using wheat bran in solid-state fermentation. Secondly, amylases hydrolyzed a rice byproduct to make a glucose-rich solution, and this sugar was finally metabolized by Saccharomyces cerevisiae to produce bioethanol. Besides, the secreted enzymes were also partially purified and characterized. The amylase activity (AA) in the crude extract was 358 U/g substrate, and the partially purified enzyme showed the best activity in the 4.0-5.5 pH range. A wide pH stability range (3.5-8.5) was confirmed. The amylase was thermostable up to 60 °C. The ion Mn⁺² (10 mM) improved by 60% the AA. There was a 54.9% yield in the conversion of rice residues into reducing sugars in 10 h. The glucose-rich solution was undergone fermentation by S. cerevisiae and showed high ethanol efficiency, 95.8% of the theoretical value. These results suggested a promising technology for bioethanol production.

Sustainability of sugarcane lignocellulosic biomass pretreatment for the production of bioethanol

The sustainability of a biofuel is severely affected by the technological route of its production. Chemical pretreatment can be considered the traditional method of decomposition of the lignocellulose into its mono and oligomeric units, which can be further bioconverted to ethanol. The evaluation of the recent advances in chemical pretreatments of sugarcane bagasse, especially diluted acids, alkaline, organosolv and ionic liquids, identified the critical points for sustainability. In this context, chemicals recovery and reutilization or their substitution by green solvents, heat and electricity generation through bioenergy, reutilization of water from evaporators, vinasse concentration and the upgrading of lignin were discussed as strategic routes for developing sustainable chemical-based lignocellulose pretreatment. The advances in the technologies that allow greater fractionation of lignocellulosic biomass should be focused on the minimization of the use of natural resources, effluent generation and energy expenditure.

Enhanced production of bacterial xylanase and its utility in saccharification of sugarcane bagasse

An investigation was carried out using sugarcane bagasse as the agricultural residue to study the optimization of xylanase production by solid-state fermentation. Maximum xylanase production (20.35 U/g substrate) was achieved by Bacillus substilis subsp. subtilis JJBS250 using 'one variable at a time approach' at pH 7.0, 40 °C after 48 h. After statistical optimization by response surface methodology (RSM) there was 4.82-fold improvement in xylanase production (98.16 U/g substrate). Further optimization of untreated and sodium carbonate pretreated sugarcane bagasse enzymatic hydrolysis was carried out using both bacterial (Bacillus substilis subsp. subtilis JJBS250) and fungal (Myceliophthora thermophila BJTLRMDU3) xylanases that showed high amount of reducing sugar liberation from untreated sugarcane bagasse (124.24 mg/g substrate) as compared to pretreated (76.23 mg/g substrate) biomass. Furthermore, biophysical characterization of untreated and sodium carbonate pretreated sugarcane bagasse using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM), revealed the structural changes in the pretreated biomass.

Fractionation of sugarcane bagasse using hydrothermal and advanced oxidative pretreatments for bioethanol and biogas production in lignocellulose biorefineries

The fractionation of sugarcane bagasse (SB) by hydrothermal pretreatment (HP, autohydrolysis) followed by alkaline extraction (AE) and advanced oxidative pretreatment (AOP) for production of second-generation ethanol and biogas was investigated. The AOP of SB was optimized using a Doehlert design, varying the applied H₂O₂ load, liquid-to-solid ratio (LSR), and time. The responses evaluated were yield (Y), residual cellulose (RC), delignification (DE), and enzymatic conversion (EC). The AE of SB pretreated by HP led to 61.8% DE (using 0.2 mol L^-1 NaOH). This high lignin removal enabled substantial savings of H₂O₂ in the AOP. The optimized AOP conditions led to 78% Y, 82.2% RC, 42.7% DE, and 88.9% EC (overall glucose yield of 60.9%). Fermentation of the enzymatic hydrolysate with Saccharomyces cerevisiae yielded 190.8 L_ethanol ton_SB^-1. Biogas production by anaerobic digestion of residual liquid streams of the pretreatment steps yielded 27.46 NL_CH4 kg_SB^-1. An energy balance was estimated for the SB fractionation.

Insight into Pretreatment Methods of Lignocellulosic Biomass to Increase Biogas Yield: Current State, Challenges, and Opportunities

Lignocellulosic biomass is recalcitrant due to its heterogeneous structure, which is one of the major limitations for its use as a feedstock for methane production. Although different pretreatment methods are being used, intermediaries formed are known to show adverse effect on microorganisms involved in methane formation. This review, apart from highlighting the efficiency and limitations of the different pretreatment methods from engineering, chemical, and biochemical point of views, will discuss the strategies to increase the carbon recovery in the form of methane by way of amending pretreatments to lower inhibitory effects on microbial groups and by optimizing process conditions.