Comparative techno-economic analysis of steam explosion, dilute sulfuric acid, ammonia fiber explosion and biological pretreatments of corn stover

Sustainable utilization of fruit and vegetable waste bioresources for bioplastics production

Nowadays, rapidly increasing production, use and disposable of plastic products has become one of the utmost environmental issues. Our current circumstances in which the food supply chain is demonstrated as containing plastic particles and other plastic-based impurities, represents a significant health risk to humans, animals, and environmental alike. According to this point of view, biodegradable plastic material aims to produce a more sustainable and greener world with a lower ecological impact. Bioplastics are being investigated as an environmentally friendly candidate to address this problem and hence global bioplastic production has seen significant growth and expansion in recent years. This article focuses on a few critical issues that must be addressed for bioplastic production to become commercially viable. Although the reduction of fruit and vegetable waste biomass has an apparent value in terms of environmental benefits and sustainability, commercial success at industrial scale has remained flat. This is due to various factors, including biomass feedstocks, pretreatment technologies, enzymatic hydrolysis, and scale-up issues in the industry, all of which contribute to high capital and operating costs. This review paper summarizes the global overview of bioplastics derived from fruit and vegetable waste biomass. Furthermore, economic and technical challenges associated with industrialization and diverse applications of bioplastics in biomedical, agricultural, and food-packaging fields due to their excellent biocompatibility properties are reviewed.HighlightsReview of the diverse types and characteristics of sustainability of biobased plasticsImproved pretreatment technologies can develop to enhance greater yieldEnzyme hydrolysis process used for bioplastic extraction & hasten industrial scale-upFocus on technical challenges facing commercialized the bioplasticsDetailed discussion on the application for sustainability of biodegradable plastics.

Mechanisms, methods and applications of machine learning in bio-alcohol production and utilization: A review

Bio-alcohols have been proven promising alternatives to fossil fuels. Machine learning (ML), as an analytical tool for uncovering intrinsic correlations and mining data connotations, is also becoming widely used in the field of bio-alcohols. This article reviews the mechanisms, methods, and applications of ML in the bio-alcohols field. In terms of mechanisms, we describe the workflow of ML applications, emphasizing the importance of a well-defined research problem and complete feature engineering for a robust model. Prediction and optimization are the main application scenarios. In terms of methods, we illustrate the characteristics of different ML models and analyze their applicability in the bio-alcohol field. The role of ML in the production of bio-methanol by pyrolysis and gasification, as well as in the three stages of fermentation for bioethanol production are highlighted. In terms of utilization, ML is used to optimize engine performance and reduce emissions. This review provides guidance on how to use novel ML methods in the bio-alcohol field, showing the potential of ML to streamline work in the whole biofuel field.

Steam explosion as sustainable biomass pretreatment technique for biofuel production: Characteristics and challenges

The biorefining process of lignocellulosic biomass has recently emerged as one of the most profitable biofuel production options. However, pretreatment is required to improve the recalcitrant lignocellulose's enzymatic conversion efficiency. Among biomass pretreatment methods, the steam explosion is an eco-friendly, inexpensive, and effective approach to pretreating biomass, significantly promoting biofuel production efficiency and yield. This review paper critically presents the steam explosion's reaction mechanism and technological characteristics for lignocellulosic biomass pretreatment. Indeed, the principles of steam explosion technology for lignocellulosic biomass pretreatment were scrutinized. Moreover, the impacts of process factors on pretreatment efficiency and sugar recovery for the following biofuel production were also discussed in detail. Finally, the limitations and prospects of steam explosion pretreatment were mentioned. Generally, steam explosion technology applications could bring great potential in pretreating biomass, although deeper studies are needed to deploy this method on industrial scales.

Comparative Analysis of Trifluoracetic Acid Pretreatment for Lignocellulosic Materials

Lignocellulosic materials are usually processed toward C5 and C6 corresponding sugars. Trifluoroacetic acid (TFA) is a pretreatment method to solubilize hemicellulose to sugars such xylose without degrading cellulose. However, this pretreatment has not been compared to other processes. Thus, this paper focuses on the techno-economic comparison of the C5-C6 production of C5-C6 as raw materials platforms using non-centrifuged sugarcane bagasse (NCSB) and Pinus patula wood chips (PP). Hydrolysates using TFA 2.5 M as an acid were characterized through HPLC regarding arabinose, galactose glucose, xylose, and mannose sugars. Then, simulations of the processes according to the experimental results were done. The economic assessment was performed, and compared with some common pretreatments. The mass and energy balances of the simulations indicate that the process can be compared with other pretreatments. From the economic perspective, the main operating expenditures (OpEx) are related to raw materials and capital depreciation due to the cost of TFA corrosion issues. The processes showed a CapEx and OpEx of 0.99 MUSD and 6.59 M-USD/year for NCSB, and 0.97 MUSD and 4.37 MUSD/year for PP, considering a small-scale base (1 ton/h). TFA pretreatment is innovative and promising from a techno-economic perspective.

Bioconversion of corn fiber to bioethanol: Status and perspectives

Due to the rising demand for green energy, bioethanol has attracted increasing attention from academia and industry. Limited by the bottleneck of bioethanol yield in traditional corn starch dry milling processes, an increasing number of studies focus on fully utilizing all corn ingredients, especially kernel fiber, to further improve the bioethanol yield. This mini-review addresses the technological challenges and opportunities on the way to achieving the efficient conversion of corn fiber. Significant advances during the review period include the detailed characterization of different forms of corn kernel fiber and the development of off-line and in-situ conversion strategies. Lessons from cellulosic ethanol technologies offer new ways to utilize corn fiber in traditional processes. However, the commercialization of corn kernel fiber conversion may be hampered by enzyme cost, conversion efficiency, and overall process economics. Thus, future studies should address these technical limitations.

Principal factors affecting the yield of dilute acid pretreatment of lignocellulosic biomass: A critical review

This review provides a critical analysis of the state of the art of dilute acid pretreatment applied to lignocellulosic biomass. Data from 63 publications were extracted and analysed. The majority of the papers used residence times of<30 min, temperature ranges from 100 °C to 200 °C, and acid levels between 0 % and 2 %. Yields are quantified directly after pretreatment (xylose content) or after enzymatic hydrolysis (glucose content). Statistical analyses allowed the time-temperature equivalence to be quantified for three types of biomass: they were formulated by non-linear expressions. In further works, investigating less explored areas, for example moderate temperature levels with longer residence times, is recommended. Pretreatment material (time-temperature kinetics, reactor type) and analytical methods should be standardized and better described. It becomes mandatory to promote the development of an open, findable, accessible, interoperable, and reusable data approach for pretreatments research.

Quantitative comparison of the delignification performance of lignocellulosic biomass pretreatment technologies for enzymatic saccharification

Pretreatments for delignification are required for the enzymatic saccharification of lignocellulosic biomasses. However, in the current literature, various pretreatment approaches have been applied for the same kinds of biomass. To find the optimum pretreatments for biomaterials containing various lignin contents, in this study, a quantitative comparison was carried out on the delignification performance of 15 categories of pretreatments. In total, 1729 sets of biomass, cellulose, hemicellulose, and lignin recovery data were collected from 214 relevant studies. Box plots and Cate-Nelson-like graphs were applied for analyses. The results showed that alkali, oxidation, organic solvent, and multistep pretreatments generally were better at removing lignin and recovering cellulose. Moreover, among these four categories, alkali pretreatments had the best performance, increasing the saccharification efficiency by approximately five-fold. Considering both delignification performance and saccharification improvement, alkali pretreatments are currently considered to be the optimum pretreatment methods for enzymatic saccharification.

Utilization of agricultural waste biomass and recycling toward circular bioeconomy

The major global concern on energy is focused on conventional fossil resources. The burning of fossil fuels is an origin of greenhouse gas emissions resulting in the utmost threat to the environment and subsequently which leads to global climate changes. As far as sustainability is concerned, fuels and materials derived from organic or plant wastes overcome this downside establishing the solution to the fossil resource crisis. In this context, exploration of agricultural residue appears to be a suitable alternative of non-renewable resources to support the environmental feasibility and meet the high energy crisis. The use of agricultural waste as a feedstock for the biorefinery approach emerges to be an eco-friendly process for the production of biofuel and value-added chemicals, intensifying energy security. Therefore, a prospective choice of this renewable biomass for the synthesis of green fuel and other green biochemicals comes up with a favorable outcome in terms of cost-effectiveness and sustainability. Exploiting different agricultural biomass and exploring various biomass conversion techniques, biorefinery generates bioenergy in a strategic way which eventually fits in a circular bioeconomy. Sources and production of agricultural waste are critically explained in this paper, which provides a path for further value addition by various technologies. Biorefinery solutions, along with a life cycle assessment of agricultural waste biomass toward a wide array of value-added products aiding the bioeconomy, are summarized in this paper.

Optimization of alkali, acid and organic solvent pretreatment on rice husk and its techno economic analysis for efficient sugar production

Excessive use of fossil fuels has accelerated climate change and global warming necessitates the need for renewable energy sources that have a lower environmental impact. In the recent decade, lignocellulosic biomass has become a prominent alternative to renewable energy resources for the production of bioenergy. The pretreatment procedure is considered a pivotal step for transforming biomass into value-added products such as sugars, biofuels, etc. Therefore, the present work aims to study the effect of different pretreatment approaches on rice husk with acids (H₂SO₄ and HCl), alkalis (NaOH and KOH), and organic solvents (ethanol and methanol) utilizing different concentrations like (2, 4 and 6% in case of acids), (2,4 and 6% for alkalis) and (50% and 70% for organic solvents) with different residence time (1, 3, 6, and 24 h). The most effective results obtained from the aforementioned steps were further adopted for enzymatic hydrolysis. Further, the changes in structural properties of biomass were assessed in relation to the pretreatment process employing scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier Transform Infrared (FTIR) analyses. This paper also highlights the techno-economic analysis of alkali pretreatment. Additionally, the operational targets for the process were identified by using a modeling software-SuperPro Designer. Results obtained from the study showed a maximum yield of reducing sugar i.e., 1.906 ± 0.2 mg/ml (4% NaOH with 6 h of incubation). This study demonstrates that 4% NaOH pretreatment effectively disintegrates the biomass and yields high sugar recovery which can be used further for the production of biofuels and value-added products.

Carbon credit reduction: A techno-economic analysis of "drop-in" fuel production

The current study elucidates the fundamentals of technical, financial, and environmental viability of the processes used for sustainable "drop-in" fuel generation. At present, the price of producing "drop-in" fuels is around two times as costly (5-6 USD/gallon) as the cost of fossil fuels (3 USD/gallon), especially when using second-generation feedstocks. Hence, this necessitates a comprehensive techno-economic understanding of the current technologies with respect to "drop-in"-fuel. This entitles technical-economic viability, and environmental sustainability to make the processes involved commercially viable. In this context, the present review addresses unique contrasts among the various processes involved in "drop-in" fuel production. Furthermore, principles and process flow of techno-economic analysis as well as environmental implications in terms of reduced carbon footprint and carbon credit are elucidated to discuss fundamentals of techno-economic analysis in terms of capital and operational expenditure, revenue, simulation, cash flow analysis, mass and energy balances with respect to evidence-based practices. Case specific techno-economic studies with current developments in this field of research with emphasis on software tools viz., Aspen Plus, Aspen HYSIS, Aspen Plus Economic Analyser (APEC) Aspen Icarus Process Evaluator (AIPE) are also highlighted. The study also emphasis on the carbon foot print of biofuels and its carbon credits (Carbon Offset Credits (COCs) and Carbon Reduction Credits (CRCs)) by leveraging a deep technical and robust business-oriented insights about the techno-economic analysis (TEA) exclusively for the biofuel production.

Extraction of Corn Bract Cellulose by the Ammonia-Coordinated Bio-Enzymatic Method

This study explored a green and efficient method for cellulose extraction from corn bract. The cellulose extraction by the CHB (CH₃COOH/H₂O₂/Bio-enzyme) method and the N-CHB (NH₃·H₂O-CH₃COOH/H₂O₂/Bio-enzyme) method were compared and analyzed. The effect of ammonia pretreatment on cellulose extraction by bio-enzymatic methods was discussed. The results showed that ammonia promoted the subsequent bio-enzymatic reaction and had a positive effect on the extraction of cellulose. Sample microstructure images (SEM) showed that the cellulose extracted by this method was in the form of fibrous bundles with smooth surfaces. The effect of different pretreatment times of ammonia on cellulose was further explored, and cellulose was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric (TG) analysis. The results showed that the N3h-CHB (NH₃·H₂O 50 °C 3 h, CH₃COOH/H₂O₂ 70 °C 11 h, Bio-enzyme 50 °C 4 h) method was the best way to extract cellulose in this study. FTIR showed that most of the lignin and hemicellulose were removed. XRD showed that all the cellulose extracted in this study was type I cellulose. TG analysis showed that the cellulose was significantly more thermally stable, with a maximum degradation temperature of 338.9 °C, close to that of microcrystalline cellulose (MCC). This study provides a reference for the utilization of corn bract and offers a new technical route for cellulose extraction.

A new l-cysteine-assisted glycerol organosolv pretreatment for improved enzymatic hydrolysis of corn stover

Deconstruction of lignocellulose via efficient pretreatment is crucial for producing fermentable sugars. In this study, effects of glycerol organosolv pretreatment (GOP) on main chemical composition of corn stover were investigated. Results indicate that the residual corn stover after 80 wt% glycerol pretreatment (at 220 °C for 0.5 h) yielded 75.97 % glucose and 78.21 % xylose after enzymatic hydrolysis, which were enhanced by 3.39- and 6.08-fold compared to the untreated corn stover. Subsequently, an l-cysteine-assisted GOP was proposed with higher yields of glucose (86.20 %) and xylose (91.13 %). When pretreating corn stover with 80 wt% glycerol containing 0.07 wt% l-cysteine at 220 °C for 0.5 h, higher fermentable sugars of 26.08 g were produced from 100 g feedstock after enzymolysis. Intrinsic mechanisms of the proposed pretreatment for enhancing enzymatic digestibility were elucidated by physiochemical characterization technologies and techno-economic analysis was also studied. This study provides guidance for fermentable sugars production from renewable lignocellulose.

Lignocellulose biohydrogen towards net zero emission: A review on recent developments

This review mainly determines novel and advance physical, chemical, physico-chemical, microbiological and nanotechnology-based pretreatment techniques in lignocellulosic biomass pretreatment for bio-H2 production. Further, aim of this review is to gain the knowledge on the lignocellulosic biomass pretreatment and its priority on the efficacy of bio-H2 and positive findings. The influence of various pretreatment techniques on the structure of lignocellulosic biomass have presented with the pros and cons, especially about the cellulose digestibility and the interference by generation of inhibitory compounds in the bio-enzymatic technique as such compounds is toxic. The result implies that the stepwise pretreatment technique only can ensure eventually the lignocellulosic biomass materials fermentation to yield bio-H2. Though, the mentioned pretreatment steps are still a challenge to procure cost-effective large-scale conversion of lignocellulosic biomass into fermentable sugars along with low inhibitory concentration.

A consolidated review of commercial-scale high-value products from lignocellulosic biomass

For decades, lignocellulosic biomass has been introduced to the public as the most important raw material for the environmentally and economically sustainable production of high-valued bioproducts by microorganisms. However, due to the strong recalcitrant structure, the lignocellulosic materials have major limitations to obtain fermentable sugars for transformation into value-added products, e.g., bioethanol, biobutanol, biohydrogen, etc. In this review, we analyzed the recent trends in bioenergy production from pretreated lignocellulose, with special attention to the new strategies for overcoming pretreatment barriers. In addition, persistent challenges in developing for low-cost advanced processing technologies are also pointed out, illustrating new approaches to addressing the global energy crisis and climate change caused by the use of fossil fuels. The insights given in this study will enable a better understanding of current processes and facilitate further development on lignocellulosic bioenergy production.

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.

A perspective on the combination of alkali pre-treatment with bioaugmentation to improve biogas production from lignocellulose biomass

Anaerobic digestion (AD) is a bioprocess technology that integrates into circular economy systems, which produce renewable energy and biofertilizer whilst reducing greenhouse gas emissions. However, improvements in biogas production efficiency are needed in dealing with lignocellulosic biomass. The state-of-the-art of AD technology is discussed, with emphasis on feedstock digestibility and operational difficulty. Solutions to these challenges including for pre-treatment and bioaugmentation are reviewed. This article proposes an innovative integrated system combining alkali pre-treatment, temperature-phased AD and bioaugmentation techniques. The integrated system as modelled has a targeted potential to achieve a biodegradability index of 90% while increasing methane production by 47% compared to conventional AD. The methane productivity may also be improved by a target reduction in retention time from 30 to 20 days. This, if realized has the potential to lower energy production cost and the levelized cost of abatement to facilitate an increased resource of sustainable commercially viable biomethane.

Surfactants in biorefineries: Role, challenges & perspectives

The use of lignocellulosic biomass (LCB) as feedstock has received increasing attention as an alternative to fossil-based refineries. Initial steps such as pretreatment and enzymatic hydrolysis are essential to breakdown the complex structure of LCB to make the sugar molecules available to obtain bioproducts by fermentation. However, these steps increase the cost of the bioproduct and often reduces its competitiveness against synthetic products. Currently, the use of surfactants has shown considerable potential to enhance lignocellulosic biomass processing. This review addresses the main mechanisms and role of surfactants as key molecules in various steps of biorefinery processes, viz., increasing the removal of lignin and hemicellulose during the pretreatments, increasing enzymatic stability and enhancing the accessibility of enzymes to the polymeric fractions, and improving the downstream process during fermentation. Further, technical advances, challenges in application of surfactants, and future perspectives to augment the production of several high value-added bioproducts have been discussed.

Resource recovery from lignocellulosic wastes via biological technologies: Advancements and prospects

Lignocellulosic wastes were recently considered as biomass resources, however, its conversion to valuable products is still immature although researchers have put lots of effort into this issue. This article reviews the key challenges of the biorefinery utilizing lignocellulosic materials and recent developments to conquer those obstacles. Available biological techniques and processes, from the pretreatments of cellulosic materials to the valorization processes, were emphasized. Biological pretreatments, including hydrolysis using microbial consortia, fungi, enzymes, engineered bacterial/fungal strains, and co-culture systems, could enhance the release of reducing sugar. Resources recovery, including biogases, ethanol, butanol, PHA, etc., from lignocellulosic materials were also discussed, while the influences of composition of lignocellulosic materials and pretreatment options, applications of co-culture system, and integrated treatments with other wastes, were described. In the review, co-culture system and metabolic engineering are emphasized as the promising biological technologies, while perspectives are provided for their future developments.

Hydrothermal pretreatment technologies for lignocellulosic biomass: A review of steam explosion and subcritical water hydrolysis

The pretreatment of lignocellulosic biomass enhances the conversion efficiency to produce biofuels and value-added chemicals, which have the potential to replace fossil fuels. Compared to physicochemical and other pretreatment techniques, the hydrothermal methods are considered eco-friendly and cost-effective. This paper reviews the strengths, weaknesses, opportunities and threats of steam explosion and subcritical water hydrolysis as the two promising hydrothermal technologies for the pretreatment of lignocellulosic biomass. Although the principle of the steam explosion in depolymerizing the lignin and exposing the cellulose fibers for bioconversion to liquid fuels is well known, its underlying mechanism for solid biofuel production is less identified. Therefore, this review provides an insight into different operating conditions of steam explosion and subcritical water hydrolysis for a wide variety of feedstocks. The mechanisms of subcritical water hydrolysis including dehydration, decarboxylation and carbonization of waste biomass are comprehensively described. Finally, the role of microwave heating in the hydrothermal pretreatment of biomass is elucidated.

Production of oligosaccharides and biofuels from Miscanthus using combinatorial steam explosion and ionic liquid pretreatment

Pretreatment strategies are fundamental to effectively deconstruct lignocellulosic biomass and economically produce biofuels, biomaterials and bio-based chemicals. This study evaluated individual and combinatorial steam explosion (SE) and ionic liquid (IL) pretreatments for production of high-value oligosaccharides from a novel seed-based Miscanthus hybrid (Mx2779). The two ILs used for pretreatment were triethylammonium hydrogen sulphate [TEA][HSO₄] and 1-ethyl-3-methylimidazolium acetate [C₂mim][OAc]. The results showed that each pretreatment leads to distinct effects on the fragmentation (cellulose and xylan dissolution, delignification, deacetylation) and physicochemical modification (cellulose and lignin properties) of lignocellulose. This, in turn, dictated enzymatic hydrolysis efficiencies of the cellulose pulp to glucose or gluco-oligosaccharides for downstream applications. Our findings suggest that the stand-alone SE or [C₂mim][OAc] pretreatments may offer cost advantages over [TEA][HSO₄] through the production of oligosaccharides such as xylo- and gluco-oligosaccharides. This study also highlights technical and economic pretreatment process challenges related to the production of oligosaccharides from Miscanthus Mx2779 biomass.

Use of Machine Learning Methods for Predicting Amount of Bioethanol Obtained from Lignocellulosic Biomass with the Use of Ionic Liquids for Pretreatment

The study objective was to model and predict the bioethanol production process from lignocellulosic biomass based on an example of empirical study results. Two types of algorithms were used in machine learning: artificial neural network (ANN) and random forest algorithm (RF). Data for the model included results of studying bioethanol production with the use of ionic liquids (ILs) and different enzymatic preparations from the following biomass types: buckwheat straw and biomass from four wastelands, including a mixture of various plants: stems of giant miscanthus, common nettle, goldenrod, common broom, fireweed, and hay (a mix of grasses). The input variables consisted of different ionic liquids (imidazolium and ammonium), enzymatic preparations, enzyme doses, time and temperature of pretreatment, and type of yeast for alcoholic fermentation. The output value was the bioethanol concentration. The multilayer perceptron (MLP) was used in the artificial neural networks. Two model types were created; the training dataset comprised 120 vectors (14 elements for Model 1 and 11 elements for Model 2). Assessment of the optimum random forest was carried out using the same division of experimental points (two random datasets, containing 2/3 for training and 1/3 for testing) and the same criteria used for the artificial neural network models. Data for mugwort and hemp were used for validation. In both models, the coefficient of determination for neural networks was <0.9, while for RF it oscillated around 0.95. Considering the fairly large spread of the determination coefficient, two hybrid models were generated. The use of the hybrid approach in creating models describing the present bioethanol production process resulted in an increase in the fit of the model to R2 = 0.961. The hybrid model can be used for the initial classification of plants without the necessity to perform lengthy and expensive research related to IL-based pretreatment and further hydrolysis; only their lignocellulosic composition results are needed.

Synthesis of polyacrylamide/polystyrene interpenetrating polymer networks and the effect of textural properties on adsorption performance of fermentation inhibitors from sugarcane bagasse hydrolysate

Economical removal of fermentation inhibitors from lignocellulosic hydrolysate plays a considerable role in bioconversion of lignocellulose biomass. In this work, the textural properties of polyacrylamide/polystyrene interpenetrating polymer networks (PAM/PS IPNs) on adsorption of fermentation inhibitors from sugarcane bagasse hydrolysate (SCBH) were investigated for the first time. The results showed that, the specific surface area, pore diameter and surface polarity had important influence on its adsorption performance towards sugars, organic acids, furans and acid-soluble lignin. The PAM/PS IPNs under the optimal copolymerization situation achieved the high selectivity coefficients of 4.07, 14.9, 21.2 and 25.8 with respective to levulinic acid, furfural, hydroxymethylfurfural (HMF) and acid-soluble lignin, and had a low total sugar loss of 2.09%. Overall, this research puts forward a design and synthetic strategy for adsorbent to remove fermentation inhibitors from lignocellulosic hydrolysate.

Chemoenzymatic conversion of Sorghum durra stalk into furoic acid by a sequential microwave-assisted solid acid conversion and immobilized whole-cells biocatalysis

In this study, chemoenzymatic conversion of Sorghum durra stalk (SDS) into furoic acid was developed by a sequential microwave-assisted solid acid conversion and immobilized whole-cells biocatalysis method. Dry dewaxed SDS (75 g/L) was catalyzed into furfural at 57.8% yield with heterogeneous Sn-argil (2.0 wt% dosage) in n-ethyl butyrate-H₂O (1:1, v:v) biphasic system using a microwave (600 W) for 10 min at 180 °C. In this biphasic media (pH 6.5), SDS-derived furfural (125.0 mM) was biologically oxidized to furoic acid by immobilized Brevibacterium lutescens cells harboring furfural-oxidizing activity at 30 °C, and furfural was wholly transformed to furoic acid within 24 h. Finally, the recovery and reuse of the Sn-argil catalyst and immobilized biocatalysts were conducted for synthesizing furoic acid from SDS in the biphasic system. This chemoenzymatic route can be attractive for furoic acid production.

Bioethanol Production from Vineyard Waste by Autohydrolysis Pretreatment and Chlorite Delignification via Simultaneous Saccharification and Fermentation

In this paper, the production of a second-generation bioethanol from lignocellulosic vineyard cutting wastes was investigated in order to define the optimal operating conditions of the autohydrolysis pretreatment, chlorite delignification and simultaneous saccharification and fermentation (SSF). The autohydrolysis of vine-shoot wastes resulted in liquors containing mainly a mixture of monosaccharides, degradation products and spent solids (rich in cellulose and lignin), with potential utility in obtaining valuable chemicals and bioethanol. The autohydrolysis of the vine-shoot wastes was carried out at 165 and 180 °C for 10 min residence time, and the resulted solid and liquid phases composition were analysed. The resulted liquid fraction contained hemicellulosic sugars as a mixture of alpha (α) and beta (β) sugar anomers, and secondary by-products. The solid fraction was delignified using the sodium chlorite method for the separation of lignin and easier access of enzymes to the cellulosic sugars, and then, converted to ethanol by the SSF process. The maximum bioethanol production (6%) was obtained by autohydrolysis (165 °C), chlorite delignification and SSF process at 37 °C, 10% solid loading, 72 h. The principal component analysis was used to identify the main parameters that influence the chemical compositions of vine-shoot waste for different varieties.

Fractionation of Waste MDF by Steam Refining

In view of the expected increase in available waste medium-density fiberboard (MDF) and the current insufficient and unsatisfactory disposal capacities, efficient ways of recycling the waste material need to be developed. In this study, the potential of steam refining as a method to hydrolyze the resins, isolate fibers, and obtain a hemicellulose-rich extract available for further utilization in the context of a biorefinery was assessed. Two different MDF waste samples, as well as poplar (Populus spp.) and spruce (Picea spp.) wood chips for benchmarking, were treated over a severity range from 2.47 to 3.95. The separated fiber and extract fractions were analyzed with regard to yield, content of carbohydrates, acids, degradation products, and nitrogen. A fiber fraction of more than 70% yield and an extract containing up to 30% of carbohydrates for further processing can be gained by steam-refining waste MDF. At low severities, most of the nitrogen-based compounds are solubilized. Increasing the severity leads to a decrease in nitrogen in the extract as the nitrogen compounds are converted into volatiles. A non-hydrolysable resin residue remains on the fibers, independent of the treatment severity. In comparison to the benchmark samples, the extract fraction of waste MDF shows a high pH of 8 and high amounts of acetic and formic acid. The generation of furfural and 5-hydroxymethylfurfural (5-HMF) on the other hand is suppressed. Distinct differences in carbohydrate hydrolysis behavior between waste MDF and conventional wood can be observed. Especially, the mannose-containing constituents seem to be resistant to hydrolysis reactions in the milieu created in MDF fractionation.

Techno-Economic Analysis (TEA) of Different Pretreatment and Product Separation Technologies for Cellulosic Butanol Production from Oil Palm Frond

Among the driving factors for the high production cost of cellulosic butanol lies the pretreatment and product separation sections, which often demand high amounts of energy, chemicals, and water. In this study, techno-economic analysis of several pretreatments and product separation technologies were conducted and compared. Among the pretreatment technologies evaluated, low-moisture anhydrous ammonia (LMAA) pretreatment has shown notable potential with a pretreatment cost of $0.16/L butanol. Other pretreatment technologies evaluated were autohydrolysis, soaking in aqueous ammonia (SAA), and soaking in sodium hydroxide solution (NaOH) with pretreatment costs of $1.98/L, $3.77/L, and $0.61/L, respectively. Evaluation of different product separation technologies for acetone-butanol-ethanol (ABE) fermentation process have shown that in situ stripping has the lowest separation cost, which was $0.21/L. Other product separation technologies tested were dual extraction, adsorption, and membrane pervaporation, with the separation costs of $0.38/L, $2.25/L, and $0.45/L, respectively. The evaluations have shown that production of cellulosic butanol using combined LMAA pretreatment and in situ stripping or with dual extraction recorded among the lowest butanol production cost. However, dual extraction model has a total solvent productivity of approximately 6% higher than those of in situ stripping model.

Life-Cycle Assessment (LCA) of Different Pretreatment and Product Separation Technologies for Butanol Bioprocessing from Oil Palm Frond

Environmental impact assessment is a crucial aspect of biofuels production to ensure that the process generates emissions within the designated limits. In typical cellulosic biofuel production process, the pretreatment and downstream processing stages were reported to require a high amount of chemicals and energy, thus generating high emissions. Cellulosic butanol production while using low moisture anhydrous ammonia (LMAA) pretreatment was expected to have a low chemical, water, and energy footprint, especially when the process was combined with more efficient downstream processing technologies. In this study, the quantification of environmental impact potentials from cellulosic butanol production plants was conducted with modeled different pretreatment and product separation approaches. The results have shown that LMAA pretreatment possessed a potential for commercialization by having low energy requirements when compared to the other modeled pretreatments. With high safety measures that reduce the possibility of anhydrous ammonia leaking to the air, LMAA pretreatment resulted in GWP of 5.72 kg CO2 eq./L butanol, ecotoxicity potential of 2.84 × 10−6 CTU eco/L butanol, and eutrophication potential of 0.011 kg N eq./L butanol. The lowest energy requirement in biobutanol production (19.43 MJ/L), as well as better life-cycle energy metrics performances (NEV of 24.69 MJ/L and NER of 2.27) and environmental impacts potentials (GWP of 3.92 kg N eq./L butanol and ecotoxicity potential of 2.14 × 10−4 CTU eco/L butanol), were recorded when the LMAA pretreatment was combined with the membrane pervaporation process in the product separation stage.

Evaluation of methane production and energy conversion from corn stalk using furfural wastewater pretreatment for whole slurry anaerobic co-digestion

In this study, corn stalk (CS) was pretreated with furfural wastewater (FWW) for whole slurry anaerobic digestion (AD), which increased the degradability of CS components, changed the parameters in pretreatment slurry and improved the biochemical methane potential (BMP). The ultimate goal was to optimize the time and temperature for FWW pretreatment and evaluate whether FWW pretreatment is feasible from BMP and energy conversion. The results of path analysis suggested that lignocellulosic degradability (LD) was the main factor affecting methane production with the comprehensive decision of 0.7006. The highest BMP (166.34 mL/g VS) was achieved by the pretreatment at 35 °C for 6 days, which was 70.36% higher than that of control check (CK) (97.64 mL/g VS) and the optimal pretreatment condition was predicted at 40.69 °C for 6.49 days by response surface methodology (RSM). The net residual value (NRV) for the pretreatment of 35 °C and 6 days was the highest (0.6201), which was the most appropriate condition for AD in real application.

Co-fermentation of magnesium oxide-treated corn stover and corn stover liquor for cellulosic ethanol production and techno-economic analysis

MgO is an effective catalyst to reduce the recalcitrant structure of corn stover and reduce sugar degradation during pretreatment. To evaluate the economic feasibility of MgO pretreatment, techno-economic analysis was performed at a commercial scale of 700,000 MT stover per year based on the collected experimental data. Compared to LHW pretreatment, MgO pretreatment reduced total capital investment due to elimination of solids washing and increased ethanol yield by 78.4 L/MT stover due to higher xylose yield (53.4 vs 10.9%), thus resulted in a lower minimum ethanol selling price (MESP) of $0.72/liter. Although washing of MgO-pretreated solids improved glucose (73.0 vs 69.5%) and xylose (66.0 vs 53.4%) yields, MESP did not decrease but increase by $0.08/liter due to the high capital cost of solid-liquid separation unit. Tween 80 also improved glucose (73.1 vs 69.5%) and xylose (62.6 vs 53.5%) yields. However, its high cost limited its economic feasibility in ethanol production.

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.

Natural freezing-thawing pretreatment of corn stalk for enhancing anaerobic digestion performance

Natural freezing-thawing (NFT) was proposed as a low energy input and alternative pretreatment method for high biomethane production from corn stalk (CS) by anaerobic digestion (AD). The CS was pretreated by freezing-thawing in winter season using different pretreatment time periods (7d, 14d, 21d and 28d) and solid-to-liquid ratios (1:2, 1:4, 1:6, 1:8 and 1:10). The results showed that CS pretreated for 21d coupled with a solid-to-liquid ratio of 1:6 achieved the best result among all pretreatment conditions. In this case, the biomethane yield and VS removal rate of CS reached the highest values of 253 mL·g_vs^-1 and 58.6%, respectively_, which were 40.5% and 27.4% higher than that of the untreated. It was also found that the predominant bacterial and archaeal at genus level in AD were Clostridium_sensu_stricto_1 (36.1%) and Methanobacterium (54.0%), respectively. This study provided that NFT is a simple pretreatment strategy for efficient AD bioconversion of CS to biomethane.

Anaerobic digestion of extracts from steam exploded Agave tequilana bagasse

Anaerobic digestion (AD) in the beverage industry is a proven treatment technology. But adding dissolved organic matter to AD can increase the on-site output of renewable energy. In the tequila industry such waste-derived organic matter can be obtained from semisolid agave bagasse submitted to steam explosion as pretreatment. Vapor at pressure <1.0 MPa is commonly available so that steam explosion can be integrated into extant production schemes. This study investigates the efficiency of agave bagasse hydrolyzation via steam explosion (applying severity factors between 2.4 and 3.7 with 0.98 MPa maximum pressure) as well as the efficiency of the bio-conversion in anaerobic batch assays. The best steam explosion yield was 14.3 ± 0.1 g_COD 100 g^-1 (0.98 MPa vapor pressure during 22 min followed by fast pressure release). The average biochemical methane potential (BMP) was 290 mL_N g_COD^-1 with 74% of the biogas released within seven days.

A novel strategy for efficient anaerobic co-digestion based on the pretreatment of corn stover with fresh vinegar residue

A novel method was advanced for efficient anaerobic co-digestion by using fresh vinegar residue (FVR) as acidifier for pretreating corn stover (CS). FVR acted as one substrate as well as an acidifier by the acids contained in FVR. It was found that the organic acids in FVR could efficiently enhance the hydrolysis of lignocellulose in CS. The biomethane production from co-digestion of FVR and CS pretreated reached 140.48 L/kg VS, which was 35.7% higher than that of unpretreated mixture substrates. The highest biomethane production was obtained when pretreatment was conducted at 150 °C. The increase of biomethane production was contributed to the improved hydrolysis of CS due to the acidic pretreatment. Pretreatment and co-digestion could improve the asynchronism and generate synergistic effect. The study provides one novel method for efficient biomethane conversion from FVR and CS.

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

This work investigated all possible process integration strategies for ethanol production from corn and dilute acid pretreated corn stover (CS) as mixed substrates. Three corn to pretreated CS ratios (20%:10%, 10%:20% and 5%:25%) were examined. When the ratio of corn to pretreated CS was 20%:10%, the process integration strategy that mixed corn with CS hydrolysate for liquefaction followed by SSF resulted in the highest ethanol titer of 99.3 g/L. Mixing liquefied corn with pretreated CS for hydrolysis/saccharification followed by fermentation was the best strategy for the other two ratios. The strategy of mixing liquefied corn with pretreated CS for 6 h hydrolysis followed by fermentation showed the highest productivity for all the tested ratios.

Techno-Economic Bottlenecks of the Fungal Pretreatment of Lignocellulosic Biomass

Fungal pretreatment is a biological process that uses rotting fungi to reduce the recalcitrance and enhance the enzymatic digestibility of lignocellulosic feedstocks at low temperature, without added chemicals and wastewater generation. Thus, it has been presumed to be low cost. However, fungal pretreatment requires longer incubation times and generates lower yields than traditional pretreatments. Thus, this study assesses the techno-economic feasibility of a fungal pretreatment facility for the production of fermentable sugars for a 75,700 m3 (20 million gallons) per year cellulosic bioethanol plant. Four feedstocks were evaluated: perennial grasses, corn stover, agricultural residues other than corn stover, and hardwood. The lowest estimated sugars production cost ($1.6/kg) was obtained from corn stover, and was 4–15 times as much as previous estimates for conventional pretreatment technologies. The facility-related cost was the major contributor (46–51%) to the sugar production cost, mainly because of the requirement of large equipment in high quantities, due to process bottlenecks such as low sugar yields, low feedstock bulk density, long fungal pretreatment times, and sterilization requirements. At the current state of the technology, fungal pretreatment at biorefinery scale does not appear to be economically feasible, and considerable process improvements are still required to achieve product cost targets.

Probabilistic Lifecycle Assessment of Butanol Production from Corn Stover Using Different Pretreatment Methods

The recalcitrant nature of lignocelluloses requires a pretreatment process before the fermentative butanol production. The commonly used pretreatment processes, such as steam explosion, sulfuric acid, ammonia fiber explosion, ionic liquid (IL), and biological, require different quantities and types of process chemicals, and produce different quality and quantity of fermentable sugars. This study determines life-cycle greenhouse gas emissions (GHG) these pretreatment methods by developing a system-level process model including corn stover feedstock supply system and the downstream butanol production process. This study further evaluates the uncertainty associated with energy use and GHG emissions for each stage of the entire butanol production chain and provide the future optimization opportunities. Probabilistic results of these analyses describe a distribution of GHG emissions with an average of 18.09-1056.12 gCO_2e/MJ and a 95% certainty to be less than 33.3-1888.3 gCO_2e /MJ. The highest GHG emissions of IL-pretreatment of 1056.12 gCO_2e/MJ reaches to 89.8 gCO_2e/MJ by switching IL-recovery from 80 to 99 wt %, which is the most influential parameter for IL-pretreatment. Additionally, credits from excess electricity, butanol yield, nitrogen replacement, and diesel fuel for transportation and harvesting were the most influential parameters. Based on the current state of technologies, apart from ionic liquid and biological pretreatments, other pretreatment processes have similar metrics of sustainability.

Enhanced sorption of hexavalent chromium [Cr(VI)] from aqueous solutions by diluted sulfuric acid-assisted MgO-coated biochar composite

Metal oxide-Carbon composites have aroused great interesting towards specific anionic contaminants removal from the polluted environment. In this study, aiming at removing toxic chromate ion [Cr(VI)] from aqueous solutions, a novel approach was developed to produce surface-enhanced MgO-coated biochar adsorbent from sugarcane harvest residue (SHR). It was found that sulfuric acid hydrolysis and MgO-coating both facilitated the removal of Cr(VI) by biochars, and the maximum sorption capacities for the pristine biochar (SHR₅₅₀), MgO-coated biochar (MgSHR₅₅₀), and acid-assisted MgO-coated biochar (MgASHR₅₅₀) that derived from the Langmuir isotherm model were 20.79, 54.64, and 62.89 mg g^-1, respectively. Additionally, the Cr(VI) removal was a pseudo-second-order kinetic model controlled process with equilibrium reached within 24 h. The mechanism investigation revealed that Cr(VI) ions was directly sorbed by the MgO-coated biochars via the chemical interaction between MgO and Cr(VI), whereas the sorption-coupled reduction of Cr(VI) to Cr(III) governed the sorption of Cr(VI) on the SHR₅₅₀. Although the increases of solution pH (>2.0) and KNO₃ concentration (>0.05 mol L^-1) reduced the Cr(VI) removal by biochars, while there were lower secondary pollution risks in MgO-coated biochar treatments due to the suppressed release of Cr(III) in solutions. This work could provide guidance for the production of efficient biochar for the removal of Cr(VI) from wastewater.

Enhanced methane production from wheat straw with the assistance of lignocellulolytic microbial consortium TC-5

The major obstacle of methane production from lignocellulose lies in the inefficient deconstruction of biomass. In this study, an anaerobic microbial consortium TC-5 was enriched with high lignocellulose-degradation capacity to enhance methane production from wheat straw. High degradation ratio of 45.7% of un-pretreated wheat straw was achieved due to a multi-species lignocellulolytic enzyme presented in the crude culture supernatant. The specific activity of xylanase, xylan esterase and β-xylosidase reached the highest level of 4.23, 0.15 and 0.48 U/mg, while cellobiohydrolase, endoglucanase and β-glucosidase showed the highest specific activity of 0.36, 0.22 and 0.41 U/mg during 9 days' degradation. Inoculation of TC-5 in digestion sludge during anaerobic digestion of wheat straw resulted in remarkable enhancement of 22.2% and 36.6% in methane yield under mesophilic and thermophilic conditions, respectively. This work demonstrates the potential of TC-5 for enhancing the production of biogas and other chemicals through biomass based biorefinery.

Enhancing bioethanol production from water hyacinth by new combined pretreatment methods

This study investigated the possibility of enhancing bioethanol production by combined pretreatment methods for water hyacinth. Three different kinds of pretreatment methods, including microbial pretreatment, microbial combined dilute acid pretreatment, and microbial combined dilute alkaline pretreatment, were investigated for water hyacinth degradation. The results showed that microbial combined dilute acid pretreatment is the most effective method, resulting in the highest cellulose content (39.4 ± 2.8%) and reducing sugars production (430.66 mg·g^-1). Scanning Electron Microscopy and Fourier Transform Infrared Spectrometer analysis indicated that the basic tissue of water hyacinth was significantly destroyed. Compared to the other previously reported pretreatment methods for water hyacinth, which did not append additional cellulase and microbes for hydrolysis process, the microbial combined dilute acid pretreatment of our research could achieve the highest reducing sugars. Moreover, the production of bioethanol could achieve 1.40 g·L^-1 after fermentation, which could provide an extremely promising way for utilization of water hyacinth.

Enhancement in multiple lignolytic enzymes production for optimized lignin degradation and selectivity in fungal pretreatment of sweet sorghum bagasse

The objective of this work was to study the increase in multiple lignolytic enzyme productions through the use of supplements in combination in pretreatment of sweet sorghum bagasse (SSB) by Coriolus versicolor such that enzymes act synergistically to maximize the lignin degradation and selectivity. Enzyme activities were enhanced by metallic salts and phenolic compound supplements in SSF. Supplement of syringic acid increased the activities of LiP, AAO and laccase; gallic acid increased MnP; CuSO₄ increased laccase and PPO to improve the lignin degradations and selectivity individually, higher than control. Combination of supplements optimized by RSM increased the production of laccase, LiP, MnP, PPO and AAO by 17.2, 45.5, 3.5, 2.4 and 3.6 folds respectively for synergistic action leading to highest lignin degradation (2.3 folds) and selectivity (7.1 folds). Enzymatic hydrolysis of pretreated SSB yielded ∼2.43 times fermentable sugar. This technique could be widely applied for pretreatment and enzyme productions.