Challenges and opportunities of lignocellulosic biomass gasification in the path of circular bioeconomy

Exploring industrial lignocellulosic waste: Sources, types, and potential as high-value molecules

Lignocellulosic biomass has a promising role in a circular bioeconomy and may be used to produce valuable molecules for green chemistry. Lignocellulosic biomass, such as food waste, agricultural waste, wood, paper or cardboard, corresponded to 15.7% of all waste produced in Europe in 2020, and has a high potential as a secondary raw material for industrial processes. This review first presents industrial lignocellulosic waste sources, in terms of their composition, quantities and types of lignocellulosic residues. Secondly, the possible high added-value chemicals obtained from transformation of lignocellulosic waste are detailed, as well as their potential for applications in the food industry, biomedical, energy or chemistry sectors, including as sources of polyphenols, enzymes, bioplastic precursors or biofuels. In a third part, various available transformation treatments, such as physical treatments with ultrasound or heat, chemical treatments with acids or bases, and biological treatments with enzymes or microorganisms, are presented. The last part discusses the perspectives of the use of lignocellulosic waste and the fact that decreasing the cost of transformation is one of the major issues for improving the use of lignocellulosic biomass in a circular economy and green chemistry approach, since it is currently often more expensive than petroleum-based counterparts.

Biofuel production: exploring renewable energy solutions for a greener future

Biofuel production has emerged as a leading contender in the quest for renewable energy solutions, offering a promising path toward a greener future. This comprehensive state-of-the-art review delves into the current landscape of biofuel production, exploring its potential as a viable alternative to conventional fossil fuels. This study extensively examines various feedstock options, encompassing diverse sources such as plants, algae, and agricultural waste, and investigates the technological advancements driving biofuel production processes. This review highlights the environmental benefits of biofuels, emphasizing their capacity to significantly reduce greenhouse gas emissions compared to those of fossil fuels. Additionally, this study elucidates the role of biofuels in enhancing energy security by decreasing reliance on finite fossil fuel reserves, thereby mitigating vulnerabilities to geopolitical tensions and price fluctuations. The economic prospects associated with biofuel production are also elucidated, encompassing job creation, rural development, and the potential for additional revenue streams for farmers and landowners engaged in biofuel feedstock cultivation. While highlighting the promise of biofuels, the review also addresses the challenges and considerations surrounding their production. Potential issues such as land use competition, resource availability, and sustainability implications are critically evaluated. Responsible implementation, including proper land-use planning, resource management, and adherence to sustainability criteria, is emphasized as critical for the long-term viability of biofuel production. Moreover, the review underscores the importance of ongoing research and development efforts aimed at enhancing biofuel production efficiency, feedstock productivity, and conversion processes. Technological advancements hold the key to increasing biofuel yields, reducing production costs, and improving overall sustainability. This review uniquely synthesizes the latest advancements across the entire spectrum of biofuel production, from feedstock selection to end-use applications. It addresses critical research gaps by providing a comprehensive analysis of emerging technologies, sustainability metrics, and economic viability of various biofuel pathways. Unlike previous reviews, this work offers an integrated perspective on the interplay between technological innovation, environmental impact, and socio-economic factors in biofuel development, thereby providing a holistic framework for future research and policy directions in renewable energy.

Lignocellulosic biomass for biochar production: A green initiative on biowaste conversion for pharmaceutical and other emerging pollutant removal

Lignocellulosic waste generation and their improper disposal has accelerated the problems associated with increased greenhouse gas emissions and associated environmental pollution. Constructive ways to manage and mitigate the pollution associated with lignocellulosic waste has propelled the research on biochar production using lignocellulose-based substrates. The sustainability of various biochar production technologies in employing lignocellulosic biomass as feedstock for biochar production not only aids in the lignocellulosic biomass valorization but also helps in carbon neutralization and carbon utilization. Functionalization of biochar through various physicochemical methods helps in improving their functional properties majorly by reducing the size of the biochar particles to nanoscale and modifying their surface properties. The usage of engineered biochar as nano adsorbents for environmental applications like dye absorption, removal of organic pollutants and endocrine disrupting compounds from wastewater has been the thrust areas of research in the past few decades. This review presents a comprehensive outlook on the up-to-date research findings related to the production and engineering of biochar from lignocellulosic biomass and their applications in environmental remediation especially with respect to wastewater treatment. Further a detailed discussion on various biochar activation methods and the future scope of biochar research is presented in this review work.

Lignocellulosic biomass fertilizers: Production, characterization, and agri-applications

The growing focus on sustainable agriculture and optimal resource utilization has spurred investigations into lignocellulosic biomass as a potential source for producing environmentally friendly fertilizers. This paper reviews recent advancements in the production and application of innovative fertilizers derived from lignocellulose. It highlights potential in enhancing agricultural productivity and reducing environmental impacts such as carbon footprint and water pollution. The paper outlines various methods for conversion, highlighting the unique advantages of chemical, enzymatic, and microbiological processes, for converting lignocellulosic biomass into nutrient-rich fertilizers. The study compares the efficacy of lignocellulosic fertilizers to traditional fertilizers in promoting crop growth, enhancing soil health, and reducing nutrient losses. The results demonstrate the potential of lignocellulosic biomass-derived fertilizers in promoting resource efficiency and sustainable agriculture. While this research significantly contributes to the existing body of knowledge, further studies on long-term impacts and scalability are recommended for the development of innovative and sustainable agricultural practices.

Conversion of locally available materials to biochar and activated carbon for drinking water treatment

For environmental sustainability and to achieve sustainable development goals (SDGs), drinking water treatment must be done at a reasonable cost with minimal environmental impact. Therefore, treating contaminated drinking water requires materials and approaches that are inexpensive, produced locally, and effortlessly. Hence, locally available materials and their derivatives, such as biochar (BC) and activated carbon (AC) were investigated thoroughly. Several researchers and their findings show that the application of locally accessible materials and their derivatives are capable of the adsorptive removal of organic and inorganic contaminants from drinking water. The application of locally available materials such as lignocellulosic materials/waste and its thermo-chemically derived products, including BC and AC were found effective in the treatment of contaminated drinking water. Thus, this review aims to thoroughly examine the latest developments in the use of locally accessible feedstocks for tailoring BC and AC, as well as their features and applications in the treatment of drinking water. We attempted to explain facts related to the potential mechanisms of BC and AC, such as complexation, co-precipitation, electrostatic interaction, and ion exchange to treat water, thereby achieving a risk-free remediation approach to polluted water. Additionally, this research offers guidance on creating efficient household treatment units based on the health risks associated with customized adsorbents and cost-benefit analyses. Lastly, this review work discusses the current obstacles for using locally accessible materials and their thermo-chemically produced by-products to purify drinking water, as well as the necessity for technological interventions.

Assessment and comparison of thermochemical pathways for the rice residues valorization: pyrolysis and gasification

Lignocellulosic biomass conversion applying thermochemical routes has been postulated as an alternative for generating renewable energy. This research compares energy-driven biorefineries based on two thermochemical routes addressed to upgrade rice husk and rice straw produced in the Department of Sucre-Colombia. Initially, this research analyzes the physico-chemical and structural characterization of the rice residues. Four different scenarios were proposed to compare the energy-driven biorefineries based on fast pyrolysis and gasification considering technical, economic, and environmental metrics. These biorefineries were simulated using the Aspen Plus V.14.0 software. The novelty of this research is focused on the identification of the biorefinery with the best techno-economic, energetic, and environmental performance in the Colombian context. Economic and environmental analyses were done by using economic metrics and emissions. From an economic perspective, the stand-alone gasification process did not have a positive economic margin. In contrast, the fast pyrolysis process has the best economic performance since this process has a positive profit margin. Indeed, scenario 1 (fast pyrolysis of both rice residues) presented an economic margin of 13.75% and emissions of 2170.92 kgCO2eq/kg for 10 years. However, this scenario was not energetically the best, holding second place due to the feedstock requirements, compared to gasification. The biorefinery scenario 1 has the best performance.

Tunnel engineering of gas-converting enzymes for inhibitor retardation and substrate acceleration

Carbon monoxide dehydrogenase (CODH), formate dehydrogenase (FDH), hydrogenase (H2ase), and nitrogenase (N2ase) are crucial enzymatic catalysts that facilitate the conversion of industrially significant gases such as CO, CO2, H2, and N2. The tunnels in the gas-converting enzymes serve as conduits for these low molecular weight gases to access deeply buried catalytic sites. The identification of the substrate tunnels is imperative for comprehending the substrate selectivity mechanism underlying these gas-converting enzymes. This knowledge also holds substantial value for industrial applications, particularly in addressing the challenges associated with separation and utilization of byproduct gases. In this comprehensive review, we delve into the emerging field of tunnel engineering, presenting a range of approaches and analyses. Additionally, we propose methodologies for the systematic design of enzymes, with the ultimate goal of advancing protein engineering strategies.

Exploitation of lignocellulosic-based biomass biorefinery: A critical review of renewable bioresource, sustainability and economic views

Urbanization has driven the demand for fossil fuels, however, the overly exploited resource has caused severe damage on environmental pollution. Biorefining using abundant lignocellulosic biomass is an emerging strategy to replace traditional fossil fuels. Value-added lignin biomass reduces the waste pollution in the environment and provides a green path of conversion to obtain renewable resources. The technology is designed to produce biofuels, biomaterials and value-added products from lignocellulosic biomass. In the biorefinery process, the pretreatment step is required to reduce the recalcitrant structure of lignocellulose biomass and improve the enzymatic digestion. There is still a gap in the full and deep understanding of the biorefinery process including the pretreatment process, thus it is necessary to provide optimized and adapted biorefinery solutions to cope with the conversion process in different biorefineries to further provide efficiency in industrial applications. Current research progress on value-added applications of lignocellulosic biomass still stagnates at the biofuel phase, and there is a lack of comprehensive discussion of emerging potential applications. This review article explores the advantages, disadvantages and properties of pretreatment methods including physical, chemical, physico-chemical and biological pretreatment methods. Value-added bioproducts produced from lignocellulosic biomass were comprehensively evaluated in terms of encompassing biochemical products , cosmetics, pharmaceuticals, potent functional materials from cellulose and lignin, waste management alternatives, multifunctional carbon materials and eco-friendly products. This review article critically identifies research-related to sustainability of lignocellulosic biomass to promote the development of green chemistry and to facilitate the refinement of high-value, environmentally-friendly materials. In addition, to align commercialized practice of lignocellulosic biomass application towards the 21st century, this paper provides a comprehensive analysis of lignocellulosic biomass biorefining and the utilization of biorefinery green technologies is further analyzed as being considered sustainable, including having potential benefits in terms of environmental, economic and social impacts. This facilitates sustainability options for biorefinery processes by providing policy makers with intuitive evaluation and guidance.

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

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

A review on the lignocellulosic derived biochar-based catalyst in wastewater remediation: Advanced treatment technologies and machine learning tools

Wastewater disposal in the ecosystem affects aquatic and human life, which necessitates the removal of the contaminants. Eliminating wastewater contaminants using biochar produced through the thermal decomposition of lignocellulosic biomass (LCB) is sustainable. Due to its high specific surface area, porous structure, oxygen functional groups, and low cost, biochar has emerged as an alternate contender in catalysis. Various innovative advanced technologies were combined with biochar for effective wastewater treatment. This review examines the use of LCB for the synthesis of biochar along with its activation methods. It also elaborates on using advanced biochar-based technologies in wastewater treatment and the mechanism for forming oxidizing species. The research also highlights the use of machine learning in pollutant removal and identifies the obstacles of biochar-based catalysts in both real-time and cutting-edge technologies. Probable and restrictions for further exploration are discussed.

Depolymerization of lignin: Recent progress towards value-added chemicals and biohydrogen production

The need for alternative sources of energy became increasingly urgent as demand for energy and the use of fossil fuels both soared. When processed into aromatic compounds, lignin can be utilized as an alternative to fossil fuels, however, lignin's complex structure and recalcitrance make depolymerization impractical. This article presented an overview of the most recent advances in lignin conversion, including process technology, catalyst advancement, and case study-based end products. In addition to the three established methods (thermochemical, biochemical, and catalytic depolymerization), a lignin-first strategy was presented. Depolymerizing different forms of lignin into smaller phenolic molecules has been suggested using homogeneous and heterogeneous catalysts for oxidation or reduction. Limitations and future prospects of lignin depolymerization have been discussed which suggests that solar-driven catalytic depolymerization through photocatalysts including quantum dots offers a unique pathway to obtain the highly catalytic conversion of lignin.

A review on modelling of thermochemical processing of biomass for biofuels and prospects of artificial intelligence-enhanced approaches

Biofuels from lignocellulosic biomass converted via thermochemical technologies can be renewable and sustainable, which makes them promising as alternatives to conventional fossil fuels. Prior to building industrial-scale thermochemical conversion plants, computational models are used to simulate process flows and conditions, conduct feasibility studies, and analyse process and business risk. This paper aims to provide an overview of the current state of the art in modelling thermochemical conversion of lignocellulosic biomass. Emphasis is given to the recent advances in artificial intelligence (AI)-based modelling that plays an increasingly important role in enhancing the performance of the models. This review shows that AI-based models offer prominent accuracy compared to thermodynamic equilibrium modelling implemented in some models. It is also evident that gasification and pyrolysis models are more matured than thermal liquefaction for lignocelluloses. Additionally, the knowledge gained and future directions in the applications of simulation and AI in process modelling are explored.

Construction of Coculture System Containing Escherichia coli with Different Microbial Species for Biochemical Production

Microbial synthesis of target chemicals usually involves multienzymatic reactions in vivo, especially for compounds with a long metabolic pathway. However, when various genes are introduced into one single strain, it leads to a heavy metabolic burden. In contrast, the microbial coculture system can allocate metabolic pathways into different hosts, which will relieve the metabolic burdens. Escherichia coli is the most used chassis to synthesize biofuels and chemicals owing to its well-known genetics, high transformation efficiency, and easy cultivation. Accordingly, cocultures containing the cooperative E. coli with other microbial species have received great attention. In this review, the individual applications and boundedness of different combinations will be summarized. Additionally, the strategies for the self-regulation of population composition, which can help enhance the stability of a coculture system, will also be discussed. Finally, perspectives for the cocultures will be proposed.

Lignin-based nanomaterials for food and pharmaceutical applications: Recent trends and future outlook

Small particles of size ranging from 1 to 100 nm are referred to as nanoparticles. Nanoparticles have tremendous applications in various sectors, including the areas of food and pharmaceutics. They are being prepared from multiple natural sources widely. Lignin is one such source that deserves special mention due to its ecological compatibility, accessibility, abundance, and low cost. This amorphous heterogeneous phenolic polymer is the second most abundant molecule in nature after cellulose. Apart from being used as a biofuel source, lignin is less explored for its potential at a nano-level. In plants, lignin exhibits cross-linking structures with cellulose and hemicellulose. Numerous advancements have taken place in synthesizing nanolignins for manufacturing lignin-based materials to benefit from the untapped potential of lignin in high-value-added applications. Lignin and lignin-based nanoparticles have numerous applications, but in this review, we are mainly focusing on the applications in the food and pharmaceutical sectors. The exercise we undertake has great relevance as it helps scientists and industries gain valuable insights into lignin's capabilities and exploit its physical and chemical properties to facilitate the development of future lignin-based materials. We have summarized the available lignin resources and their potential in the food and pharmaceutical industries at various levels. This review attempts to understand various methods adopted for the preparation of nanolignin. Furthermore, the unique properties of nano-lignin-based materials and their applications in fields including the packaging industry, emulsions, nutrient delivery, drug delivery hydrogels, tissue engineering, and biomedical applications were well-discussed.

Boosting hydrogen production via deoxygenation-sorption-enhanced biomass gasification

Gasification is one of the most promising approaches to accomplishing efficient utilization of biomass, nevertheless, it shows severe problems of low efficiency and syngas quality, which deserves further improvements. In this regard, deoxygenation-sorption-enhanced biomass gasification is proposed and experimentally explored using deoxidizer-decarbonizer materials (xCaO-Fe) for intensified hydrogen production. The materials follow the deoxygenated looping of Fe⁰-3e^-↔Fe³⁺ as an electron donor and the decarbonized looping of CaO + CO₂ ↔ CaCO₃ as a CO₂ sorbent. Specifically, the H₂ yield and CO₂ concentration reach 7.9 mmol·g^-1 biomass and 10.5 vol%, which increases by 311% and decreases by 75%, respectively, compared with conventional gasification, confirming the promotion effect of deoxygenation-sorption enhancement. Fe embedded within the CaO phase is successfully constructed with the formation of functionalized interface structure, affirming the strong interaction between CaO and Fe. This study brings in a new concept for biomass utilization via synergistic deoxygenation and decarbonization, which will substantially boost high-quality renewable hydrogen production.

Optimization of Alkaline Extraction of Xylan-Based Hemicelluloses from Wheat Straws: Effects of Microwave, Ultrasound, and Freeze-Thaw Cycles

The alkaline extraction of hemicelluloses from a mixture of three varieties of wheat straw (containing 40.1% cellulose, 20.23% xylan, and 26.2% hemicellulose) was analyzed considering the following complementary pre-treatments: freeze-thaw cycles, microwaves, and ultrasounds. The two cycles freeze-thaw approach was selected based on simplicity and energy savings for further analysis and optimization. Experiments planned with Design Expert were performed. The regression model determined through the response surface methodology based on the severity factor (defined as a function of time and temperature) and alkali concentration as variables was then used to optimize the process in a multi-objective case considering the possibility of further use for pulping. To show the properties and chemical structure of the separated hemicelluloses, several analytical methods were used: high-performance chromatography (HPLC), Fourier-transformed infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (¹H-NMR), thermogravimetry and derivative thermogravimetry analysis (TG, DTG), and scanning electron microscopy (SEM). The verified experimental optimization result indicated the possibility of obtaining hemicelluloses material containing 3.40% glucan, 85.51% xylan, and 7.89% arabinan. The association of hot alkaline extraction with two freeze-thaw cycles allows the partial preservation of the hemicellulose polymeric structure.

Opportunities and challenges of machine learning in bioprocesses: Categorization from different perspectives and future direction

Recent advances in machine learning (ML) have revolutionized an extensive range of research and industry fields by successfully addressing intricate problems that cannot be resolved with conventional approaches. However, low interpretability and incompatibility make it challenging to apply ML to complicated bioprocesses, which rely on the delicate metabolic interplay among living cells. This overview attempts to delineate ML applications to bioprocess from different perspectives, and their inherent limitations (i.e., uncertainties in prediction) were then discussed with unique attempts to supplement the ML models. A clear classification can be made depending on the purpose of the ML (supervised vs unsupervised) per application, as well as on their system boundaries (engineered vs natural). Although a limited number of hybrid approaches with meaningful outcomes (e.g., improved accuracy) are available, there is still a need to further enhance the interpretability, compatibility, and user-friendliness of ML models.

Microwave processing of oil palm wastes for bioenergy production and circular economy: Recent advancements, challenges, and future prospects

The valorization and conversion of biomass into various value-added products and bioenergy play an important role in the realization of sustainable circular bioeconomy and net zero carbon emission goals. To that end, microwave technology has been perceived as a promising solution to process and manage oil palm waste due to its unique and efficient heating mechanism. This review presents an in-depth analysis focusing on microwave-assisted torrefaction, gasification, pyrolysis and advanced pyrolysis of various oil palm wastes. In particular, the products from these thermochemical conversion processes are energy-dense biochar (that could be used as solid fuel, adsorbents for contaminants removal and bio-fertilizer), phenolic-rich bio-oil, and H₂-rich syngas. However, several challenges, including (1) the lack of detailed study on life cycle assessment and techno-economic analysis, (2) limited insights on the specific foreknowledge of microwave interaction with the oil palm wastes for continuous operation, and (3) effects of tunable parameters and catalyst's behavior/influence on the products' selectivity and overall process's efficiency, remain to be addressed in the context of large-scale biomass valorization via microwave technology.

Syngas production and gas-N evolution over heterogeneously doped La-Fe-O perovskite-type oxygen carriers in chemical looping gasification of microalgae

Chemical looping gasification (CLG) is a promising technology for syngas production with low pollutant emission. In this study, doped La-Fe-O perovskites including LaFeO₃ (LF), LaFe_0.5Ni_0.5O₃ (LN5F5) and La_0.3Ba_0.7FeO₃ (L3B7F) were developed for microalgae CLG. The as-prepared perovskites exhibited an outstanding performance in syngas production with accumulative syngas yield > 33 mol/kg. For gas-N evolution, perovskites were beneficial to the formation of NH₃ and HCN, while the iron ore may convert precursors to NO. Below 400 °C, NO_x can be stored on the perovskite surface in the form of nitrite/nitrate species. When the temperature was above 700 °C, NO_x can be selectively reduced by reducing components in tar or syngas under the catalysis of L3B7F, resulting in the final reduction of NO_x emission. Thus, CLG over L3B7F may be a promising way for efficient utilization of microalgae to overcome the intractable nitrogen-related obstacles in the commercial application of biomass gasification technologies.

One pot bioprocessing in lignocellulosic biorefinery: A review

Practically, high-yield conversion of biomass into value-added products at low cost is a primary goal for any lignocellulosic refinery. In the industrial context, the limitation in the practical adaptation of the conventional techniques practically involves multiple reactors for the conversion of biomass to bioproducts. Therefore, the present manuscript critically reviewed the advancements in one-pot reaction systems with a major focus on the scientific production of value-added products from lignocellulosic biomass. In view of that, the novelty of one-pot reactions is shown during the fractionation of biomass into their individual constituents. The importance of the direct conversion of cellulose and lignin into a range of valuable products including organic acids and platform chemicals are separately discussed. Finally, the article is concluded with the opportunities, existing troubles, and possible solutions to overcome the challenges in lignocellulosic biorefinery. This article will assist the readers to identify the economic-friendly-one-pot conversion of lignocellulosic biomass.

Household food waste conversion to biohydrogen via steam gasification over copper and nickel-loaded SBA-15 catalysts

Household food waste (FW) was converted into biohydrogen-rich gas via steam gasification over Ni and bimetallic Ni (Cu-Ni and Co-Ni) catalysts supported on mesoporous SBA-15. The effect of catalyst method on steam gasification efficiency of each catalyst was investigated using incipient wetness impregnation, deposition precipitation, and ethylenediaminetetraacetic acid metal complex impregnation methods. H₂-TPR confirmed the synergistic interaction of the dopants (Co and Cu) and Ni. Furthermore, XRD and HR-TEM revealed that the size of the Ni particle varied depending on the method of catalyst synthesis, confirming the formation of solid solutions in Co- or Cu-doped Ni/SBA-15 catalysts due to dopant insertion into the Ni. Notably, the exceptional activity of the Cu-Ni/SBA-15-EMC catalyst in FW steam gasification was attributed to the fine distribution of the concise Ni nanoparticles (9 nm), which resulted in the highest hydrogen selectivity (62 vol%), gas yield (73.6 wt%). Likewise, Cu-Ni solid solution decreased coke to 0.08 wt%.