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Pyrolysis of biomass residues into biochar is seen as a feasible way to mitigate climate change by biological carbon storage (carbon dioxide removal, CDR) and to substitute fossil fuel with sustainable biofuel. This study applies a combination of flash and ramp heating pyrolysis, and organic petrography to investigate the hydrocarbon (biofuel) potential and biochar stability and morphotypes of eight brown, red, and green macroalgal species of different tissue complexity. The carbon stability of biochar derived from macroalgae has not previously been assessed using organic petrography (reflectance measurements) and evaluated in the context of the geological carbon cycle. The biochar, hydrocarbon, and CO + CO 2 yields vary due to different chemical composition of the macroalgal species, but the product yield variations are not related to the brown, red, or green macroalgal groups. The total biofuel yield shows an inverse trend with biochar yield. A slower heating rate produces more biochar and higher CO + CO 2 and lower biofuel yields than the combined flash pyrolysis and faster heating rate. The morphotype composition of the biochar was qualitatively examined by reflected light microscopy while carbon stability was assessed by random reflectance (R o) measurements. The diverse morphotype compositions observed in biochar formed under similar pyrolysis conditions likely stem from variations in the original algal composition. While some biochar samples show morphologies resembling the original macroalgal structure, porous morphotypes predominantly characterize the biochar samples overall. Despite a maximum pyrolysis production temperature (PT) of 650 °C, the highest mean R o value among all biochar samples is 2.91%, corresponding to a carbonization temperature (CT) of 526 °C. This observation is tentatively related to the less lignocellulosic structure of the macroalgae compared to terrigenous biomass. Four biochar samples have their entire R o distribution range above the inertinite benchmark (IBR o 2%) of R o = 2% indicating high carbon stability. Conversely, the remaining four biochar samples exhibit R o distributions extending below IBR o 2%, indicating the presence of a carbon fraction with lower long-term stability in soil. The statistically significant inverse relationship observed between the mean R o values and the peak hydrocarbon generation temperature (T max) can be attributed to the behavior of residual macromolecules within the biochar. When these macromolecules reach peak biofuel generation at a lower temperature, they undergo carbonization over a more extended time interval during pyrolysis. Consequently, this prolonged exposure to the pyrolysis process leads to higher degrees of carbonization, as reflected by higher R o values. In conclusion, the findings from pyrolysis and organic petrography reveal: (1) Macroalgae demonstrate potential for biofuel production, although biofuel yields contingent upon both the species of macroalgal and the heating rate employed, and (2) This study documents for the first time that flash+ramp pyrolysis of macroalgae yields biochar suitable for long-term carbon storage. However, both the carbon stability inferred from R o frequency distributions and biochar yields show variations across different macroalgal species and heating rate. • Biofuel yield shows an inverse trend with biochar yield. • Slower heating rate produces higher biochar and CO + CO 2 and lower biofuel yields. • Biochar from macroalgae is dominated by porous morphotypes. • Biochar formation from macroalgae is usable for both CDR and biofuel production. • Carbon stability is dependent on the macroalgal species and the heating rate. [ABSTRACT FROM AUTHOR]

Enormous annual sewage sludge (SS) volumes pose global environmental challenges owing to contamination and significant greenhouse gas emissions. Here, we investigated the economic viability of co-pyrolyzing SS and biomass waste to produce biofuels (bio-oil and gas) and biochar. Net present worth (NPW) analysis, the sale product break-even price, and sludge handling price (SHP) were used to determine the profitability of co-pyrolysis compared with SS pyrolysis alone and conventional treatment methods. In this study, the sale prices of biochar based on quality (i.e., stability, carbon sequestration effectiveness, and heavy metal content) were estimated to be 2.24, 1.44, and 0.98 CAD/kg for high-, medium-, and low-grade biochar. The bio-oil prices, estimated based on the higher heating values of bio-oil and diesel, ranged from 0.80 to 1.22 CAD/kg. Sawdust (SD) and wheat straw (WS) were the chosen co-pyrolysis feedstocks, with four mixing ratios (20, 40, 60, and 80 wt%). Economically, SD (40 wt% mixing ratio) co-pyrolysis achieved the best performance, with a maximum NPW of 8.71 million CAD. SD single and co-pyrolysis were the only profitable scenarios. Moreover, SS single pyrolysis and WS co-pyrolysis exhibited higher profitability than conventional SS treatment methods, with SHPs of 65 and 40 CAD/1000 kg dry sludge, respectively. Sensitivity analysis highlighted the dependence of economic performance on biochar and bio-oil market value. This study offers the first economic analysis of this approach and enhances our understanding of the potential of co-pyrolysis for biofuel and biochar production, providing innovative solutions for the environmental challenges of SS disposal. [Display omitted] • Cost, operating expenses, and energy recovery of a pyrolysis plant were evaluated. • Co-pyrolyzing SS with sawdust SS showed the highest NPW of 8.71 million CAD. • All single and co-pyrolysis cases showed higher revenue than SS disposal methods. • Economic feasibility was dependent on bio-oil and biochar quality and sales price. [ABSTRACT FROM AUTHOR]

[Display omitted] Biochar, a solid carbonaceous substance synthesized from the thermochemical degradation of biomass, holds significant potential in addressing global challenges such as soil degradation, environmental pollution, and climate change. Its potential as a carbon sequestration agent, together with its versatile applications in soil amendments, pollutant adsorption, and biofuel production, has garnered attention. On the other hand, microalgae, with their outstanding photosynthetic efficiency, adaptability, and ability to accumulate carbohydrates and lipids, have demonstrated potential as emerging feedstock for biochar production. However, despite the significant potential of microalgal biochar, our current understanding of its various aspects, such as the influence of parameters, chemical modifications, and applications, remains limited. Therefore, this review aims to provide a comprehensive analysis of microalgae-based biochar, covering topics such as production techniques, pollutant removal, catalytic applications, soil amendments, and synthesis of carbon quantum dots to bridge the existing knowledge gap in this field. [ABSTRACT FROM AUTHOR]

• CO 2 helps to modify properties of biochar made via pyrolysis. • Porosity of biochar can be improved when CO 2 is used in the pyrolysis. • The modification approach can be applied to precisely engineer biochar for various applications. Biochar is widely used for various environmental remediation strategies such as soil amendment because of its intrinsic carbon negativity and porosity. Biochar is a charcoal-like material produced via pyrolysis of biomass. To determine an effective method for modification of the porosity and morphology of biochar and establishment of a more sustainable pyrolysis platform for biomass valorization, this study used CO 2 as a reactive gas medium in the biomass pyrolysis process. This study placed emphasis on elucidating the role of CO 2 in the production of biochar from different types of biomass, such as cellulose, xylan, lignin, grass, and oak wood. The surface area and porosity of biochar were strongly related to the type of biomass. Under comparable pyrolysis conditions, the surface area of biochar decreased in the following order: cellulose > xylan > lignin ∼ oak wood > grass. The use of CO 2 as the gas medium in biomass pyrolysis affected the surface area and porosity of biochar samples derived from biomass feedstock. For instance, the surface area and total pore volume of the oak-wood-derived biochar produced in the CO 2 environment were twice those produced in the N 2 environment. Given that the increases in the biochar surface area and porosity were attributed to the enhanced release of volatile organic compounds (VOCs) from biomass, CO 2 may have enhanced VOC release (removal) during pyrolysis. Therefore, the use of CO 2 in a pyrolysis platform is expected to be a strategic approach for biomass valorization. [ABSTRACT FROM AUTHOR]

The world's growing population and industrial activities have led to increased energy demand and the depletion of fossil fuels, causing environmental pollution and global warming. A paradigm shift from fossil fuel resources to sustainable energy sources is therefore inevitable. The production of biofuel, such as biochar, from biomass has been receiving increased research attention due to its benefits, which address several environmental issues while advancing the circular economy and sustainable development. This manuscript presents a comprehensive overview of the conversion of coconut biomass residue into biochar, focusing on production methods, physicochemical properties, and versatile applications. Various techniques that have been used for coconut biochar production, including pyrolysis, gasification, torrefaction, and hydrothermal carbonization, are examined in detail, considering their potential for sustainable resource utilization. The interplay between production parameters and resultant biochar characteristics is underscored, elucidating the influence of feedstock composition, pyrolysis conditions, and activation procedures. The findings revealed that the produced biochar has been employed in wastewater treatment, soil amendment, and carbon sequestration, among others. This vast application is a result of the biochar's distinct physicochemical properties, including high porosity, substantial surface area, the presence of several surface functional groups, and thermal stability. Notwithstanding, biochar production from coconut residues faces several challenges. These challenges were addressed in this review, and relevant recommendations were proposed. [Display omitted] • Biochar from coconut residues is obtained from thermochemical processes. • Its properties have made it very efficient in a wide variety of applications. • Production faces challenge from feedstock seasonality. • Concerns also exist around the environmental impact of thermochemical processing. [ABSTRACT FROM AUTHOR]

[Display omitted] • Greywater derived microalgae used to produce biochar via microwave pyrolysis. • Biochar has high heating value of 28.3 MJ/Kg, comparable to coal. • BET surface area and pore volume of biochar is 121.3 m2/g and 0.3 cc/g. • Fixed carbon and carbon content of biochar increased by 193.6% and 42.3%. • The biofuel production process had a net energy balance of + 11.32 MJ/Kg. Biochar was produced from polyculture microalgae cultivated in greywater using microwave pyrolysis. The highest biochar yield and fixed carbon content of 49.9% and 68.7% were obtained at microwave power (P) of 800 W and reaction time (T) of 8.6 min. The developed quadratic models, 166.96 – 0.23P – 3.87 T – 3.49 x10-3PT + 1.73 x10-4P2 + 0.13 T2 and – 73.79 + 0.29P + 1.86 T – 1.80 x10-4P2 could predict biochar yield and fixed carbon content respectively with errors of 6.2 and 7.9%. The volatile matter (VM), fixed carbon (FC), and high heating value (HHV) of the biomass were 69.2%. 23.4% and 17.6 MJ/Kg, respectively. VM, FC, and HHV for biochar obtained at optimum conditions were 20.2%, 68.7%, and 28.3 MJ/Kg, respectively. The process had a net positive energy balance of 11.32 MJ/Kg and energy efficiency of 1.76. This study paves the way for biochar production from greywater-grown microalgae, contributing to waste valorization and energy sustainability. [ABSTRACT FROM AUTHOR]

• A sulfonated biochar is prepared by sulfonation method of 4-chlorobenzenesulfonic acid. • The sulfonated biochar have a strong hydrophobic network and acid density. • The catalyst is highly active for the esterification reactions. • The catalyst is active and selective for alkylation reactions. • The catalyst is stable for five runs. Catalytic esterification of fatty acid with methanol, alkylation of 4-ethylphenol with benzyl alcohol as well as 2-methylfuran with cyclopentanone are of great significant for the production of biofuels. However, the in-situ produced water decreases the acidity of catalyst and induces side reaction, leading to an unsatisfactory catalytic activity and selectivity. Herein, a novel biochar-based hydrophobic benzenesulfonic acid is prepared for the first time by one-pot sulfonation method of biochar with 4-chlorobenzenesulfonic acid. It has a large specific surface area of 100-400 m2/g, a hydrophobicity with H 2 O contact angle higher than 110° and a high concentration of sulfonic acid over 1.0 mmol/g. In the esterification reaction of fatty acid with methanol for synthesis of biodiesel, it shows a higher conversion of 96.0% than sulfonic acid resin amberlyst-15 (86.7%) and traditional sulfonated biochar-SO 3 H (28.0%). In the alkylation reaction of 4-ethylphenol with phenylmethanol/2-methylfuran with cyclopentanone for high-density bicyclic/monocyclic biofuel, its catalytic efficiency with target product yields are 69.4% and 70.5% respectively, which are also higher than that of amberlyst-15 (74.3%, 49.4%) and biochar-SO 3 H (14.7%, 13.0%). Furthermore, the catalyst is more stable than biochar-SO 3 H. The preparation of hydrophobic biochar-based sulfonic acid catalysts not only opens a new way for high-value utilization of biochar, but also provides a novel efficient catalyst in many acid-catalyzed transformation reactions that the product H 2 O causes deleterious effects. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Valorization of red mud and lipid waste via the thermo-chemical process. • Enhanced energy recovery in the thermo-chemical process using CO 2. • Fabrication of biochar composite from red mud and lipid waste. • Biodiesel synthesis using biochar composite. Abstract Co-pyrolysis of lipid waste and red mud was investigated to achieve valorization of red mud by fabricating biochar composite. For the further sustainable approach, this study intentionally employed carbon dioxide (CO 2) as reaction medium in the co-pyrolysis process. The use of CO 2 on co-pyrolysis of lipid waste and red mud enabled manipulation of the carbon distributions between pyrogenic products. CO 2 expedited the thermal cracking of lipid waste and further reacted with lipid waste during the thermolysis. These mechanistic roles of CO 2 were catalytically enhanced by the presence of mineral phases (Fe 2 O 3) in red mud, thereby resulting in the enhanced formation of CO (40 times more at 550 °C). However, CO 2 suppressed dehydrogenation of lipid waste (∼ 50%), which resulted in the different pathway for reducing iron oxide in red mud. Moreover, as an aspect of valorization of red mud, catalytic capability of biochar composite was evaluated. As a case study, biodiesel (FAMEs) were synthesized, and all experimental findings suggested that biochar composite could be an effective catalyst for biodiesel synthesis. As compare to biodiesel synthesis using silica (92% yield at 360 °C), the equivalent biodiesel yield was achieved with the biochar at much lower temperature (130 °C). [ABSTRACT FROM AUTHOR]

Abstract In spite of tremendous efforts and huge investments on resources, biodiesel from oleaginous microalgae has not yet become a commercially viable and sustainable alternative to petro-diesel. This is mainly because of the technological and economic challenges hovering around large scale cultivation and downstream processing of algae, water and land usage, stabilized production technology, market forces and government policies on alternative energy and carbon credits. This review attempts to capture and analyse the global trends and developments in the areas of biofuel and bio-product of microalgae and proposes possible strategies that can be adopted to produce biofuel, biochar and bio-products utilizing wastewater in a bio-refinery model. The strategies include "Zero waste discharge" concept with process integration, wherein microalgae is grown strategically using different wastewater combined with flue gas in cultivation system for simultaneous production of 'high-value-low-volume' product and 'low-value-high-volume' product with sharing of the remnant biomass to produce biochar. In addition, the CO 2 present in the atmosphere is captured and sequestered long term in the form of biochar would help to attain carbon negativity, while remediating wastewater and balancing energy requirements. Therefore, "Zero waste discharge" concept holds the potential to make the process a sustainable one, while gaining on the carbon credits. Graphical abstract Unlabelled Image Highlights • Analysis of the trends and developments of biofuel and bio-product from microalgae • Microalgae provide an edge over lignocellulosic and solid waste based feedstock. • "Zero waste discharge" concept with process integration is presented. • Parallel synthesis of high value product and biochar as a co-product [ABSTRACT FROM AUTHOR]

Abstract This work investigated the optimization of process parameters in the upgrading of the oil extracted from Scenedesmus obliquus microalgae using a novel nickel-impregnated biochar catalyst. The effects of temperature, dodecane-to-oil mass ratio and pressure on the upgraded liquid-phase biofuel yield were evaluated and optimized by central composite design of the response surface methodology (RSM). The model equation generated from RSM showed that dodecane-to-oil mass ratio and pressure, as well as the quadratic effects of all the three factors, were significant model terms in predicting the yield of upgraded liquid-phase biofuel. Maximum liquid biofuel yield was attained at 246.89 °C, 3.72 (w/w) dodecane-to-oil mass ratio, 3.84 MPa hydrogen pressure and 6 h processing time. Validation runs resulted in an upgraded biofuel yield of 69.4%, which was in close agreement with predicted values generated by RSM. The upgraded biofuel comprised of 100% green liquid hydrocarbons containing 94% alkanes and 6% alkenes. Its main fuel properties, such as heating value (43.78 MJ kg−1), elemental composition, density, and viscosity, exceeded those of the fatty acid methyl ester standard and were found comparable to those of petroleum diesel. More importantly, the results of the ultimate analysis and confirmed by the findings from Fourier transform infrared and gas chromatography – mass spectroscopy analyses, showed significantly low oxygen and nitrogen content and absence of sulfur in the upgraded biofuel. Graphical abstract Image Highlights • Novel catalyst was synthesized from rice hull biochar. • The catalyst was used to upgrade Scenedesmus obliquus oil to high-quality biofuel. • Response surface methodology was used to optimize biofuel yield. • High optimum biofuel yield at 69.4 wt. % was obtained. • The biofuel consisted of 100% green liquid hydrocarbons and HHV of 43.78 MJ kg−1. [ABSTRACT FROM AUTHOR]

Highlights • Uncertainty in market prices drives financial outcomes. • Monte Carlo simulation allows uncertainty to be quantified. • Biochar-only production offers a potentially profitable venture. • Biofuel-biochar coproduction requires RINs to achieve financial success. Abstract A comparative techno-economic analysis of two different thermochemical biomass conversion pathways was conducted to examine the effects of fuel price and other variables on project financial performance. Monte Carlo simulation was used to quantify the effects of uncertainty and volatility of ten critical variables: biofuel, biochar and feedstock prices, discount rate, capital investment, labor cost, loan terms, feedstock drying, and biofuel and biochar conversion rates. Market prices for biofuel and biochar have the largest impact on net present value (NPV) of any variable considered, due in part to the high levels of uncertainty associated with future prices of both. Across the ranges of input values for these variables in simulation analysis, hearth-based pyrolysis biochar production had the highest likelihood of profitability with a mean NPV of $41.5 million and only 20% of outcomes resulting in a net loss, while 68% of outcomes for auger-based biochar-biofuel coproduction represented a financial loss, including a mean NPV of -$24.2 million. However, when additional revenue from Renewable Identification Numbers (RINs) credits generated by biofuel production is considered, financial outcomes of biochar-biofuel coproduction improve to 50% likelihood of experiencing a net loss. Findings of the very strong impact of market prices on financial outcomes, relative to other important technical and economic variables, can inform effective targeting of future renewable energy policy, as well as the design of future techno-economic analyses, which do not currently focus on the effect of market prices on profitability. [ABSTRACT FROM AUTHOR]

• Microalgal tolerate heavy through different heavy metal uptake strategies. • Role of different transporters in the uptake and detoxification of heavy metals. • Microalgae based strategies for bioremediation of specific heavy metals. • Microalgae show elevated biomass and lipid production under metal stress. The proficiency of microalgae to resist heavy metals has potential to be beneficial in resolving various environmental challenges. Global situations such as the need for cost-effective and ecological ways of remediation of contaminated water and for the development of bioenergy sources could employ microalgae. In a medium with the presence of heavy metals, microalgae utilize different mechanisms to uptake the metal and further detoxify it. Biosorption and the next process of bioaccumulation are two such major steps and they also include the assistance of different transporters at different stages of heavy metal tolerance. This capability has also proved to be efficient in eradicating many heavy metals like Chromium, Copper, Lead, Arsenic, Mercury, Nickel and Cadmium from the environment they are present in. This indicates the possibility of the application of microalgae as a biological way of remediating contaminated water. Heavy metal resistance quality also allows various microalgal species to contribute in the generation of biofuels like biodiesel and biohydrogen. Many research works have also explored the capacity of microalgae in nanotechnology for the formation of nanoparticles due to its relevant characteristics. Various studies have also revealed that biochar deduced from microalgae or a combination of biochar and microalgae can have wide applications specially in deprivation of heavy metals from an environment. This review focuses on the strategies adopted by microalgae, various transporters involved in the process of tolerating heavy metals and the applications where microalgae can participate owing to its ability to resist metals. [ABSTRACT FROM AUTHOR]

[Display omitted] • The rise of cellulosic ethanol generates vast amounts of lignin-rich residues. • Unique opportunity to apply lignin depolymerization technologies at scale. • Lignin bio-oil is upgradable into liquid biofuels and aromatic biochemicals. • Biochar can be a valuable coproduct of lignin depolymerization. • Many research opportunities in this novel platform of biorenewables. Recent years witnessed the dawn of the cellulosic ethanol industry based on enzymatic hydrolysis of carbohydrates in lignocellulosic biomass. Meanwhile, new concepts have emerged to depolymerize lignin and upgrade the obtained lignin fragments into value-added fuels and chemicals. This review analyzes the convergence of these two fields, presenting the opportunities for applying such depolymerization technologies to the residual enzymatic hydrolysis lignin (EHL) now available at an industrial scale. Key characteristics of EHL are presented together with the most investigated technologies for EHL depolymerization (pyrolysis, hydrothermal, and solvolysis) to obtain lignin bio-oils. The review also discusses the prospects for upgrading lignin bio-oils for use as aviation and marine biofuels. Furthermore, it presents a more long-term vision that progressively valorizes the biochar by-product and adds the co-production of chemicals harnessing the aromaticity and oxygenation of the lignin moieties. In conclusion, EHL has a unique set of characteristics (cost, availability, transportability, degrees of oxygenation and purity, reactivity, among others) to produce lignin bio-oils, instigating research questions dedicated to this type of industrially relevant feedstock. [ABSTRACT FROM AUTHOR]

Biochar derived from orchid tree leaves is utilised as the fuel of a direct carbon solid oxide fuel cell (DC-SOFC), with yttrium stabilized zirconia (YSZ) as electrolyte and cermet of silver and gadolinium doped ceria (Ag-GDC) as the material of both cathode and anode, operating without any liquid medium or feeding gas. The performance of the DC-SOFC operated on the leaf char is higher than that operated on the best reported carbon fuel for DC-SOFCs, Fe-loaded activated carbon. XRD, Raman spectroscopy, SEM and EDX are applied to characterize the leaf char. It turns out that the leaf char is with porous structure and there is much Ca along with some K and Mg uniformly distributing in the leaf char. The effects of the naturally existing alkaline earth metal and alkaline metal and their distribution on the performance of the DC-SOFCs operated on the leaf char are analyzed in detail. [ABSTRACT FROM AUTHOR]

[Display omitted] • Application of Fe-impregnated bentonite as a catalyst in pyrolysis of grass cut. • CO 2 gas was employed as a pyrolysis gas medium. • Fe-impregnated bentonite enhanced syngas production. • Fe-impregnated bentonite induced formation of methyl 1,1-methyl-dodecanoate (C 14 H 28 O 2). • Obtained biochar had good As(V) adsorption capability. Fe-impregnated bentonite was employed in CO 2 -assisted pyrolysis of grass cut as a catalyst to improve syngas production, bio-oil quality, and biochar sorptive property. The gas analysis revealed that H 2 and CO production was enhanced by 332 and 7,110%, respectively, by applying Fe-impregnated bentonite in pyrolysis of grass cut while untreated bentonite had a limited influence on syngas production. Bio-oil produced from Fe-impregnated bentonite and grass cut (Fe-BG) had more homogenized chemical species in bio-oil as compared to that produced from pyrolysis of grass cut, and contained methyl 1,1-methyl-dodecanoate (C 14 H 28 O 2), one of the major components in biodiesel. The produced biochar had high surface area (69.2 m2 g−1) and possessed Fe0 and graphitic carbon structure, which was deemed to arise from reduction of Fe-oxides by syngas. Biochar also showed high As(V) adsorption capacity. The overall results of this work demonstrated the beneficial utility of Fe-impregnated bentonite in pyrolysis of biomass to improve syngas production as well as the quality of pyrogenic products. [ABSTRACT FROM AUTHOR]

[Display omitted] • The eminence of lowering carbon footprint to mitigate climate change. • Application of lignocellulosic biomass, microorganisms and algae in bio-energy generation. • Carbon capture and sequestration by novel MOFs, MXenes and nanocomposites. • Acumen in achieving Sustainable Development Goals through the implementation of the Clean Development Mechanism. Global industrialisation and overexploitation of fossil fuels significantly impact greenhouse gas emissions, resulting in global warming and other environmental problems. Hence, investigations on capturing, storing, and utilising atmospheric CO 2 create novel technologies. Few microorganisms, microalgae, and macroalgae utilise atmospheric CO 2 for their growth and reduce atmospheric CO 2 levels. Activated carbon and biochar from biomasses also capture CO 2. Nanomaterials such as metallic oxides, metal-organic frameworks, and MXenes illustrate outstanding adsorption characteristics, and convert CO 2 to carbon-neutral fuels, creating a balance between CO 2 production and elimination, thus zeroing the carbon footprint. The need for a paradigm shift from fossil fuels and promising technologies on renewable energies, carbon capture mechanisms, and carbon sequestration techniques that help reduce CO 2 emissions for a better tomorrow are reviewed to achieve the world's sustainable development goals. The challenges and possible solutions with future perspectives are also discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crop residues (CR) are promising sustainable feedstocks for biochars and biofuels. • CR biochars are produced by pyrolysis and hydrothermal carbonization. • CR biochars could be applied in catalytic reactions for biodiesel and biogas. • Tar can be cracked using CR biochar and metal-loaded biochar. • CR supply, biochar production, and utilization for biofuel production are addressed. A sustainable carbon-neutral society is imperative for future generations, and biochars and biofuels are inevitable choice to achieve this goal. Crop residues (CR) such as sugarcane bagasse, corn stover, and rice husk are promising sustainable resources as a feedstock for biochars and biofuels. Extensive research has been conducted on CR-based biochar production not only in environmental remediation areas but also in application for biofuel production. Here, the distribution and resource potential of major crop residues are presented. The production of CR-biochar and its applications in biofuel production processes, focusing on the latest research are discussed. Finally, the challenges and areas of opportunity for future research in terms of CR supply, CR-biochar production, and CR-biochar utilization for biofuel production are proposed. Compared with other literature reviews, this study can serve as a guide for the establishment of sustainable, economical, commercial CR-based biorefineries. [ABSTRACT FROM AUTHOR]

• Poultry litter biochar produced at 700 °C (PLB700) enhanced syngas fermentation. • PLB700 outperformed switchgrass biochar made at 350 °C or 700 °C (SGB350, SGB700). • Strain P7 produced more ethanol and butanol in media with PLB700 and SGB700. • Strain P11 produced more ethanol and acetic acid in media with PLB700 and SGB700. • Biochar enhanced syngas fermentation due to favorable physicochemical properties. Biochar feedstock and production method affects its physicochemical properties and subsequent application. This study investigated the effects of biochar from switchgrass (SGB) and poultry litter (PLB) produced at 350 and 700 °C on alcohol formation using CO:CO 2 :H 2 (40:30:30) by Clostridium carboxidivorans (P7) and C. ragsdalei (P11). Fermentations were performed in 250 mL bottles with a 50 mL working volume at 37 °C. Strains P7 and P11 produced 1.2- to 2.2-fold more alcohol and consumed 1.2- to 1.9-fold more syngas using biochars made at 700 °C compared to 350 °C. Both strains also produced 1.4- to1.9-fold more alcohol with both biochars made at 700 °C compared to control without biochar. Strain P11 produced 1.1- and 1.6-fold more alcohol and fatty acids, respectively, in medium with PLB made at 700 °C compared to strain P7. These results provide guidance towards the selection of biochar type and production temperature to improve syngas fermentation. [ABSTRACT FROM AUTHOR]

Two different pathways for utilizing Miscanthus giganteus biochar were evaluated, namely, for the production of sustainable solid biofuels and as a precursor of high surface area activated carbons. Biochars were produced through a simple thermochemical conversion method via pyrolysis at 400, 500, 600, and 800 °C. The obtained biochars and raw biomass were characterized in detailed by proximate and ultimate analyses. The thermal behaviour and structural and strength properties were evaluated. The chemical composition (cellulose, hemicellulose, and lignin content) of raw Miscanthus giganteus was investigated. The biochars afforded a sufficient higher heating value (HHV) of up to 32 MJ kg−1. Activated carbon was obtained via chemical activation with KOH at 800 °C. The effect of the pyrolysis temperature on the surface properties of the activated carbons was investigated over a wide temperature range. The resulting activated carbons were characterised by N 2 adsorption–desorption at −196 °C and by determining the pH of aqueous extracts. As a potential application, the obtained activated carbon series was used for the adsorptive removal of isoproturon from aqueous media. The adsorption capacity was as high as 384 mg g−1 and depended on the pore size distribution of the activated carbons. The conducted study follows the current trend of search for novel energy sources and water purification. [Display omitted] • Miscanthus giganteus biochar was produced by pyrolysis at 400–800 °C. • Pyrolysis temperature affected properties of biochar and activated carbon. • The higher heating value of biochar pyrolysed at 600 °C was 32.8 MJ kg−1. • Biochar was used as precursor of activated carbon with high specific surface area. • Activated carbon efficiently adsorbed isoproturon from aqueous solution. [ABSTRACT FROM AUTHOR]

In this paper, the use of grape marc for energy purposes was investigated. Grape marc is a residual lignocellulosic by-product from the winery industry, which is present in every world region where vine-making is addressed. Among the others, hydrothermal carbonization was chosen as a promising alternative thermochemical process, suitable for the treatment of this high moisture substrate. Through a 50 mL experimental apparatus, hydrothermal carbonization tests were performed at several temperatures (namely: 180, 220 and 250 °C) and residence times (1, 3, 8 h). Analyses on both the solid and the gaseous phases obtained downstream of the process were performed. In particular, solid and gas yields versus the process operational conditions were studied and the obtained hydrochar was evaluated in terms of calorific value, elemental analysis, and thermal stability. Data testify that hydrochar form grape marc presents interesting values of HHV (in the range 19.8–24.1 MJ/kg) and physical–chemical characteristics which make hydrochar exploitable as a solid biofuel. In the meanwhile, the amount of gases produced is very small, if compared to other thermochemical processes. This represents an interesting result when considering environmental issues. Statistical analysis of data allows to affirm that, in the chosen range of operational conditions, the process is influenced more by temperature than residence time. These preliminary results support the option of upgrading grape marc toward its energetic valorisation through hydrothermal carbonization. [ABSTRACT FROM AUTHOR]

Lignocellulosic model compounds and aspen wood are processed at supercritical hydrothermal conditions to study and understand feedstock impact on biocrude formation and characteristics. Glucose and xylose demonstrate similar yield of biocrude and biochar, similar biocrude characteristics, and it is hypothesized that reaction mechanisms for the two model compounds are indistinguishable. Glucose and xylose are main sources of substituted cyclopentenones and substantial contributors to oxygenated aromatics mainly in the range of C 6 –C 9 number of carbon atoms, and potential, sustainable biogasoline candidates. Lignin yields predominantly aromatic biocrudes having similar C 6 –C 9 number of carbon atoms. Model mixtures show good predictability in the distribution of substituted cyclopentenones and oxygenated aromatics, but aspen wood-derived biocrude is more aromatic than predicted by model mixtures. The work extends previous work on the understanding of the chemical mechanisms of lignocellulose liquefaction and the biocrude formation. Potential applications for the biocrudes are identified, where significant sustainability issues for the transport sector can be addressed. [ABSTRACT FROM AUTHOR]

Oil palm wastes (OPWs) are important biomass resources, and approximately 127 million tons of OPWs are generated from the oil palm industry annually in Malaysia. The scientific and reasonable utilization of OPWs is essential to economic and environmental sustainability in the country. Pyrolysis is a mature and revolutionary technology that can convert OPWs into biofuel. The conversion of OPWs into biofuel is in accordance with the national conditions of Malaysia and can simultaneously address the problems of fossil fuel shortage and environmental deterioration. Therefore, Malaysia is the most active country in the research of OPWs pyrolysis and has achieved fruitful results. Bio-oil produced from the catalytic co-pyrolysis of OPWs with hydrogen-rich materials exhibits remarkable fuel properties. Biochar generated from OPWs pyrolysis presents huge application potential as an absorbent, catalyst, soil conditioner, and carbon sequestration agent. Consequently, the paper provides a comprehensive review of OPWs pyrolysis and lays the foundation for the exploitation of OPWs resources. [Display omitted] • Malaysia is the most active country in the research of OPWs pyrolysis. • Effects of reactors and conditions on OPWs pyrolysis are detailed. • OPWs-based biochar exhibits great application potential in various fields. • Building a pyrolysis plant near the oil palm mill is a viable and economic method. • OPWs pyrolysis has great commercial potential and economic value in Malaysia. [ABSTRACT FROM AUTHOR]

Microwave-assisted catalytic pyrolysis (MACP) is a low-carbon emission and economically feasible technology for co-producing biofuels and biochar from biomass. [Display omitted] • MACP coupled with low-carbon electricity mix is a promising negative emission technology. • The use of electricity for MACP biofuel production generates significant GHG reduction without sacrificing the travel distance of vehicles compared to directly charged EVs. • The application of biochar has significant impacts on economic and environmental performances of MACP system. • MACP biofuel will be competitive in price compared to petroleum fuels by 2026 under the planned carbon tax schedule in Canada. • The co-production of biofuel and biochar brings flexibility to the biorefinery to seek the highest possible economic and environmental benefits. The conversion of forest residues into biofuels will enhance the decarbonization of the transportation sector and help the world reach its net-zero targets. Microwave-assisted catalytic pyrolysis (MACP) is an emerging thermo-catalytic conversion technology which, when coupled with low-carbon electricity, will result in negative emissions. The work described here assessed the economic feasibility and environmental impact of a novel MACP system for co-production of upgraded biofuel and high-quality biochar from forest residues. The cradle-to-gate (CTG) carbon intensity of MACP biofuel ranged from −57.3 to 27.4 g CO 2 -eq/MJ respectively when using either low-carbon electricity or carbon-intense electricity. Compared to petroleum fuels, a 43% to 162% reduction of GHG emissions could be achieved depending on electricity mix and methods to treat biochar co-product. The use of electricity to produce MACP biofuel as compared to directly charge electric vehicles was justified as a preferred use based on the finding that the advanced utilization of waste biomass via MACP could contribute significantly to GHG reduction of transportation fuel without sacrificing the travel distance of vehicles. The minimum selling price (MSP) of MACP biofuel was $1.02/L in the absence of any policy support and could be reduced to a comparable price of petroleum fuels at $0.53/L or increased to $1.32/L depending on the co-product revenue from biochar's higher or lower-value applications. MACP biofuel could also be priced competitively with petroleum fuels by as early as 2026 under the planned carbon tax schedule in Canada. This co-production of upgraded biofuel and value-added biochar could bring flexibility to the biorefinery to seek the highest possible economic and environmental benefits facing the changing market and policy. [ABSTRACT FROM AUTHOR]

Renewable energy sources such as biomass have been proven to be one of the promising sustainable alternatives to fossil fuels. However, using biomass directly as a fuel is less attractive due to its high moisture content, poor grindability, low bulk density, and low energy density nature. Hence biomass can be converted into biochar to overcome these challenges. In this study, biochar was derived from citrus peels biomass by slow pyrolysis over the temperature range of 300–700 °C. The effect of pyrolysis temperature on the quality of citrus peels-derived biochar was examined based on the physical and chemical properties obtained from various analyses. The citrus peels biomass and biochar were characterized by means of higher heating value (HHV) analysis, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDX), Fourier transform infrared ray (FTIR) analysis, proximate and thermogravimetric analysis. Based on the characterization results, the potential usage of the derived biochar as a solid fuel was discussed. Results obtained from the pyrolysis experiments indicated that a lower pyrolysis temperature produced a higher char yield. The carbon content and energy content of biochar were found to be increasing with pyrolysis temperature. Biochar produced at 500 °C presented the best fuel properties by having the highest value of HHV and carbon content. The results from this study provided great insights into biomass waste reutilisation to generate value-added biochar for renewable energy production in Malaysia. [Display omitted] • Promising potential for citrus peels biomass to biochar for energy conversion. • Higher heating value of citrus peels biochar comparable to sub-bituminous coal. • Carbon and energy content increased with increasing pyrolysis temperature. • Better combustion stability for biochar of higher pyrolysis temperature. [ABSTRACT FROM AUTHOR]

• Conversion of algae biomass into bio-oil, biochar and biogas using hydrothermal liquefaction. • Algae is considered as a potential source due to its rapid growth and high flexibility. • The pathway of HTL involves de-polymerization, de-composition and recombination. • Carbohydrates, lipids and proteins which are the primary constituents of an algal biomass. Algae, a potential biomass feedstock with a faster growth rate and capability of greenhouse gas absorption, mitigates the limitations of the first- and second-generation feedstock in bio-oil production. hydrothermal liquefaction (HTL) is known to be an active method capable of producing substantial energy resources. In HTL, biomass undergoes thermal depolymerization in the presence of water, at around 280 °C–350 °C following subcritical and near supercritical conditions to produce chemical compounds such as alkanes, nitrogenates, esters, phenolics, etc. The primary product, "Biocrude/Bio-oil" obtained from the reaction, is identified as the essential fuel source after processing and also as a distinct value-added chemical source, along with biochar and biogas as co-products. This review outlines a range of routes available for thermochemical conversion of the algal biomass. It also provides a better understanding of the reaction mechanism like depolymerization, decomposition, and re-polymerization, operating conditions like temperature, pressure, the quantity of catalyst required, and the solvent used in the process. The review also highlights the yield achieved by altering the aforementioned parameters, comparing and presenting them as a collective result. [ABSTRACT FROM AUTHOR]

The continuous development of the economy and the constant improvement of living standards have stimulated the development of animal husbandry. This development has been accompanied by the massive production of animal manure with various bad odors and high heavy metal content, constituting severe damage to ecological security and human health. Traditional disposal methods, including composting and anaerobic digestion, are difficult to achieve satisfactory results due to long processing time, water and soil eutrophication, and toxic gas emissions. However, converting animal manure into bioenergy through pyrolysis is a clean, safe, and promising technique to reduce the amount of waste and produce valuable products. Co-pyrolysis with other materials can decrease the content of heavy metals in biochar and ameliorate the properties of products. The application of catalysts influences the pyrolysis process and product properties positively. The objective of this review is to analyze the properties of animal manure and discuss the recovery of biofuel from harmful animal manure by pyrolysis. A comprehensive analysis of animal manure pyrolysis and related product characteristics will provide a foundation for the sustainable management and scientific disposal of hazardous manure waste. [Display omitted] • Biochar is the primary product of conventional pyrolysis of animal manure. • High temperature enhances the immobilization of heavy metals in biochar. • Co-pyrolysis promotes the reduction of heavy metal content. • The addition of co-feedstock or catalyst influences product properties greatly. [ABSTRACT FROM AUTHOR]

[Display omitted] • Renewable biofuel production by algal biomass has been discussed in this review. • Two major thermochemical process like pyrolysis and hydrothermal liquefaction are described. • Different pyrolysis and HDL methods in fuel production has been explained. • Temperature, heating rate of the process and product yield have been focused. • Challenges and future benefits of the fuel production using algal biomass is detailed. Renewable and sustainable biofuel production from algal biomass has been explored vigorously due to the owing potential of overcoming the limitations of first and second-generation biofuel feedstocks. Thermochemical conversion technologies are considered promising routes for bioenergy production from algal biomass and have been extensively investigated over the last few years. This paper aims to review the various pyrolysis (slow, fast, and microwave -assisted) processes and hydrothermal liquefaction (HTL) techniques. The fast pyrolysis is involving a higher heating rate and shorter residence time compared to slow pyrolysis. Microwave-assisted pyrolysis (MAP) is considered a highly efficient process due to uniform heating. Due to a high moisture feedstock, the HTL process is considered the most energy-efficient processing option for algal biomass. In all these processes, the process temperature is considered the most critical parameter affecting product yield. This paper provides a detailed analysis and discussion on the effect of temperature and heating rates on the product (biochar, bio-oil, and syngas) yields for various microalgal species. The process details, different approaches, and process conditions investigated, challenges and recent advancements achieved in both technologies have been discussed in detail that provides useful insights to design a sustainable process and understand the process feasibility. [ABSTRACT FROM AUTHOR]

This study investigated activated sludge (AS) dewatering and reuse for solid biofuel by novelty combining and a low H 2 O 2 dose and pulse ultrasonication followed by torrefaction to achieve zero-waste with the supernatant also recycled for nutrient supply to the AS unit. Mass and volume reduction rates are employed to evaluate the AS dewatering efficiency, and the biochar characteristics were systematically evaluated using higher heating value (HHV), mass and energy yield, proximate and ultimate analyses, and combustibility. The energy return on investment (EROI), greenhouse gas (GHG) emissions, and cost-effectiveness of the proposed technology were also systematically evaluated. Results showed that the mass and volume reduction rates of AS using an H 2 O 2 concentration of 0.8 % with ultrasonication at 70 W for 20 s was higher than 50 % and promoted the release of protein and carbohydrate content in the supernatant. Torrefaction of residual AS produced biochar with HHV of 17.8–18.4 MJ/kg. The biochar with 57.4 % less GHG emissions than burning bituminous coal, high EROI (4.7–7.3), but a low fuel ratio. Thus, we propose co-firing 10–20 % biochar with coal to enhance the FRs to that of bituminous coal while simultaneously mitigating GHG emissions. The production cost of biochar was 56.3 % lower than the traditional AS disposal cost. Therefore, the proposed technology is environmentally and economically friendly and can solve sludge disposal problems, produce biochar with reasonable cost for renewable energy, mitigate global warming, and recover supernatant as a nutrient feedstock. It is worth developing practical applications in this field. • The integrated technology involving low H 2 O 2 dose, pulse ultrasonication, and torrefaction achieved biofuel production and zero-waste. • Rich protein and hydrocarbon can be recovered as a nutrient source for the activated sludge unit. • Substituting the produced biochar for bituminous coal reduced 57.4 % CO 2 emission. • The EROIs of the biochar were high (4.7–7.3) and suitable for sustainable reuse. • An economic perspective with 56.3% less cost than the traditional sludge disposal. [ABSTRACT FROM AUTHOR]

Abstract: A partial solution to problems associated with anthropogenic greenhouse gas (GHG) emissions could be the development and deployment of carbon-negative technologies, i.e., producing energy while reducing atmospheric carbon dioxide levels. Biofuels have been considered a possibility but have faced limitations due to competition with food production and GHG emissions through indirect land-use change (ILUC). In this article, we show how emissions from ILUC can potentially be reduced by producing food and bioenergy from biochar amended soils. The possibility of yield improvements from biochar would reduce the land requirement for crop production and thus, lead to a reduction in emissions from ILUC. In our application, biochar and bio-oil are produced via fast pyrolysis of corn stover. Bio-oil is subsequently upgraded into a fuel suitable for use in internal combustion engines. Applying the U.S. regulatory method used to determine biofuel life cycle emissions, our results show that a biochar-induced yield improvement in the U.S. Midwest ranging from 1% to 8% above trend can lead to an ILUC credit between 1.65 and 14.79 t CO2-equivalent ha−1 year−1 when future emissions are assessed over the next 30 years. The model is generalizable to other feedstocks and locations and illustrates the relationship between biochar and crop production. [Copyright &y& Elsevier]

The Antarctic krill, referring to Euphausia superba , feeds phytoplankton, grown up with photosynthesis for CO 2 fixation. Therefore, the use of krill as a raw feedstock for energy production is a highly carbon negative approach, not disturbing the food supply chain of human. Although the krill has high lipid content (up to 40 wt%, dry basis), its use as a raw feedstock for biodiesel production has not been considered. In this study, the feasibility of Euphausia superba to be used as a biodiesel feedstock was scrutinized. Prior to biodiesel production, an annual biodiesel production potential from the krill without disruption of ecosystems was estimated (129% larger than current biodiesel production in Korea). Because krill oil contains high fraction impurities, (trans)esterification with acid catalyst resulted in low yield of biodiesel (6.5 wt%), while non-catalytic transesterification achieved 94.7 wt% of biodiesel yield. To maximize the utilization of krill, solid residue obtained after biodiesel production was synthesized to krill biochars, and they were used as sorptive materials for adsorption of toxic chemicals. Among different model pollutants (Cd(II), Cr(VI), and methylene blue), krill biochar had the best adsorption capacity for Cd(II) (13.7 mg g−1), which is comparable value with other studies. [Display omitted] Biodiesel production from transesterification of lipid in krill and conversion of krill solid residue into biochar, available for adsorption of environmental pollutants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electricity-enhanced ANP mixotrophy was investigated for the first time. • Electricity-enhanced mixotrophy with MV or biochar showed carbon efficiency of >80%. • Alcohol/acid ratio of 0.402 mol/mol was achieved with MV and electricity. • The carbon efficiency obtained was the highest reported in C. carboxidivorans. Anaerobic, non-photosynthetic mixotrophy (ANP mixotrophy) is a process whereby glucose consumption and CO 2 fixation via the Wood-Ljungdahl pathway occur concurrently. ANP mixotrophy supplemented with exogenous reducing power and CO 2 shows the potential of reducing the carbon loss from glycolysis and enhancing the production of biofuels. Previous studies used H 2 and syngas as the exogenous source of reducing power, however, the low solubility of H 2 and CO impeded their efficient utilization by bacteria. This study used a bio-electrochemical system (BES) to supply electrons to fix CO 2 and shift the metabolite profiles towards more-reduced products in acetogenic bacteria Clostridium carboxidivorans. C. carboxidivorans showed no electroactivity, but the electricity-enhanced fermentation without electron mediator showed higher alcohol production and carbon efficiency compared to open-circuit fermentation. C. carboxidivorans could fix CO 2 autotrophically with the electrical current and electron mediator MV or biochar. Electricity-enhanced mixotrophy with MV showed a higher alcohol/acid ratio and carbon efficiency in liquid products (0.402 mol/mol and 82.8%, respectively) compared to those without MV and electricity (0.067 mol/mol and 52.2%, respectively). The addition of biochar in electricity-enhanced mixotrophy increased the carbon efficiency to 80.3%, and promoted the synthesis of butyrate and hexanoate. This study investigated the electricity-enhanced ANP mixotrophic fermentation for the first time, and demonstrated its potential for enhancing carbon efficiency and alcohol production with C. carboxidivorans. [ABSTRACT FROM AUTHOR]

Abstract: Biomass thermochemical decomposition products have been extensively studied as renewable substitutes of fossil fuel. The approach proposed in this work considers vegetal waste as a source of both energy and matter through the production of a vapor phase fuel, highly diluted in steam, suitable to be burned in non-conventional combustion systems and a char with soil amending and fertilizing properties. To demonstrate the feasibility of such a process an experimental set-up has been designed with the aim to investigate the effect of pressure, heating rate and final temperature in proper variation ranges (P =1–5×105 Pa, HR=5–40K/min, T =473–973K) on the yields and on the chemical and physical properties of gaseous and solid products. In this paper the effect of temperature at constant pressure (P =5×105 Pa) and heating rate (HR=5K/min) has been investigated in order to explore all the stages of the thermochemical degradation from torrefaction to mild gasification passing through devolatilization. For real biomasses a basic study on characterization of biomass components is needed. Knowledge of dependences on feedstock nature and process conditions is crucial for the comprehension of phenomena occurring during steam pyrolysis of real complex biomasses and for the optimization of the process operating variables. This study characterizes steam pyrolysis up to 873K (at pressure P =5×105 Pa and heating rate HR=5K/min) both of three single biomasses constituents (cellulose, hemicellulose and lignin) and of three binary mixtures in order to evaluate possible interactions between the biomass components. The results obtained highlight the importance of the interactions between components, mainly cellulose and lignin, on the yield and characteristics of solid and gaseous products. In particular, strong components interactions have been detected on the specific surface area of the solid product. [Copyright &y& Elsevier]

Abstract: This study was designed to investigate the effect of anaerobic digestion on biochar produced from sugarcane bagasse. Sugarcane bagasse was anaerobically digested to produce methane. The digested residue and fresh bagasse was pyrolyzed separately into biochar at 600°C in nitrogen environment. The digested bagasse biochar (DBC) and undigested bagasse biochar (BC) were characterized to determine their physicochemical properties. Although biochar was produced from the digested residue (18% by weight) and the raw bagasse (23%) at a similar rate, there were many physiochemical differences between them. Compared to BC, DBC had higher pH, surface area, cation exchange capacity (CEC), anion exchange capacity (AEC), hydrophobicity and more negative surface charge, all properties that are generally desirable for soil amelioration, contaminant remediation or wastewater treatment. Thus, these results suggest that the pyrolysis of anaerobic digestion residues to produce biochar may be an economically and environmentally beneficial use of agricultural wastes. [ABSTRACT FROM AUTHOR]

The growing health and environmental concerns associated with the consumption of fossil energy sources catalyze the production of biofuels as renewable energy carriers for heat and electricity generation. Production of biofuels from biomass, being the most available renewable feedstock, is advantageous as it results in increased mitigation of GHGs (greenhouse gas) emissions. Co-firing biomass pellet in power plants is a promising way of using biomass for renewable energy generation. Among the various thermochemical conversion routes, torrefaction represents an efficient low-temperature pyrolysis technology to produce co-firing biofuel at 200–300 °C with low conversion losses. However, the current practice of using conventional heating in batch operation adversely affects oil palm torrefaction, leading to low throughput, low biomass processing rate, and poor heat transfer rate. Integration of microwave technology has emerged as a promising solution to enhance the upscaling capacity of torrefaction technology, offering higher production rates and better volumetric heat transfer. The present work critically reviews and discusses the latest developments in the torrefaction of oil palm waste to produce energy-dense biochar with reduced moisture content (for better water resistivity and durability). The use of microwave radiation as a heating method could also catalyze the torrefaction reaction with lower activation energy. In conclusion, microwave systems incorporated into continuous reactors seem to have great potential in streamlining torrefaction processes, thereby producing environmentally friendly energy. [Display omitted] • Reactor design for the continuous torrefaction process of oil palm waste is reviewed. • Oil palm waste is a potential feedstock for conversion into energy-dense biochar. • Continuous microwave torrefaction is a promising, fast, and efficient approach. • Microwave-assisted torrefaction can be up scaled to operate in continuous operation. • Moving bed, rotating drum, auger, and conveyor belt mechanism are promising designs. [ABSTRACT FROM AUTHOR]

• Pyrolysis of halophyte S. bigelovii (seed and seedless-plant) has been investigated. • S. bigelovii seed pyrolysis liquid is ~80% bio-oil, while seeds-less plant is ~90% aqueous phase. • S. bigelovii biochars are not recommended for soil amendment but for carbon sequestration. • S. bigelovii seed has good potentials for biofuels production in arid and semi-arid regions. The development of bioenergy in marginal environments has been hampered by the lack of sustainable sources of biomass. The halophyte Salicornia bigelovii , has been found to adapt extremely well in a desert climate. In this study, the S. bigelovii seed and the seedless-plant have been assessed, for the first time, for biofuel and biochar production through thermochemical conversion (pyrolysis) in an auger reactor operated at 550 °C. Both feedstocks showed significant differences in chemical composition, with the seed being closer to the characteristics of seeds from common oilseed crops. The S. bigelovii seed produced high bio-oil yield (79.9% of total liquid) of high pH predominated with fatty acids commonly found in vegetable oils. The S. bigelovii seedless-plant produced a liquid of significantly low bio-oil (10% of total liquid) with an aqueous phase of pH and salinity close that of brackish water. The biochars were of moderate heating value and limited potentials for soil amendment due to the high ash content in the biomass, but are reasonably stable for long term carbon sequestration due to their low O/C and H/C ratios (<0.1 and <1.0, respectively). Comparative assessment in terms of the conversion efficiency and renewability indicated that pyrolysis of the S. bigelovii seed offers a good opportunity for biofuel production in arid/semi-arid saline regions against the alternative option of transesterification conversion. [ABSTRACT FROM AUTHOR]

• Biochar and hydrochar was produced from pyrolysis and HTC, respectively. • Biochar composition and its significance over other catalyst was highlighted. • Underlying mechanism of biochar catalyst facilitated fuel production was given. • Biochar catalyst was used in transesterification, biohydrogen, biomass hydrolysis. Thermochemical routes namely pyrolysis, hydrothermal carbonization, torrefaction and hydrothermal liquefaction yields biochar product, which mainly contains carbon, oxygen and hydrogen. Biochar produced can be activated to employ as a potential catalyst in various energy production applications like transesterification and fermentation. In this regard, this article has comprehensively reviewed the biochar based catalyst for fuel production. Initially, biochar produced from various thermochemical routes and its yield was presented. Composition of biochar produced from sundry feedstock was reviewed and the reason for choosing biochar catalyst for fuel production was discussed. Eventually, mechanism by which the biochar catalyst facilitates the fuel production was given for better understanding. Transesterification and esterification reaction for biodiesel, biomass hydrolysis process and biohydrogen production facilitated by biochar catalyst were extensively discussed. [ABSTRACT FROM AUTHOR]

• Biochar obtained from thermochemical methods can be activated by various strategies. • Physical viz., steam and CO 2 based activation of biochar is used. • Activation of biochar by H 2 O 2 , KOH, ZnCl 2 , K 2 CO 3 are chemical methods. • Activated biochar has improved surface area, pore size and minimal contaminants. • Activated biochar is used as catalyst for biodiesel production. Microalgae and macroalgae are known for their use in food and fuel applications. Recently, tremendous interest on algal biomass for biochar production has been increased. Biochar are well known for its catalytic activity to produce many finished products such as alternative fuels, treat environmental waste water and act as an input for agricultural applications. Three routes are commonly adopted for alternative fuel production from algal biomass namely, biochemical, chemical, and thermochemical techniques. Recently, thermochemical methods for the conversion of algal biomass to biochar are employed to use biochar based catalyst. Biochar must be activated before used as a potential catalyst. Therefore, this review has given broad information of various activation strategies for biochar modification. Different activation methods such as physical and chemical modes are being practiced to modify the biochar for efficient catalyst in alternative fuel production. [ABSTRACT FROM AUTHOR]

Thermochemical methods namely pyrolysis, gasification/hydrothermal gasification, combustion, hydrothermal liquefaction and hydrothermal carbonization are widely practiced to convert algal biomass into fuels. Among the methods, pyrolysis, and hydrothermal liquefaction are most commonly practised to convert numerous algal biomasses into bio-oil and/or biochar to substitute crude oil in petroleum refinery. In this regard, this review is focused on the conversion of various microalgal; and cyanobacterial biomasses into bio-oil, and solid char products through pyrolysis and hydrothermal liquefaction. Initially, pyrolysis and hydrothermal liquefaction of algal biomass on bio-oil and biochar yield have been reviewed. As the composition and yield of bio-oil from algae depends on the reaction temperature, detailed account of the impact of temperature on the quantity and quality of bio-oil and solid char obtained from pyrolysis and hydrothermal liquefaction were comprehensively presented in the review. Eventually, this article provides opportunities and scope in the pyrolysis and hydrothermal liquefaction of algae for further research. [ABSTRACT FROM AUTHOR]

• Hydrothermal liquefaction is an effective method for the conversion of biomass into biofuel. • Selection of appropriate catalyst is important for achieving high bio-oil yields with high quality. • Catalytic hydrothermal liquefaction of biomass to biofuel are discussed in detail. Hydrothermal liquefaction (HTL) is an effective method for the conversion of biomass into biofuel involving moderate temperature and high pressure. However, the yield and quality of bio-oil are not sufficient for commercialization under normal HTL conditions. In this regard, the review emphasizes the need to select the appropriate catalyst for achieving high bio-oil yields with improved quality. Besides, the factors influencing the catalytic HTL, including the types of catalyst used in HTL, the mechanism of catalytic-HTL reaction, the effect of the catalyst on other HTL products including biochar, aqueous phase extracts, and gas, are discussed in detail. This review also summarizes by mentioning the barriers to be overcome in catalytic HTL by focusing on promising approaches. [ABSTRACT FROM AUTHOR]

• The combustibility test proved that the compaction process contributes to greater burning efficiency. • The pelletizing process promoted a higher energy density of coffee husk pellets. • Higher pyrolysis temperatures promoted higher production of phenolic compounds. • Higher pyrolysis temperatures have made biochars more aromatic and carbonaceous. The growing market for pellets used to produce energy requires research on new feedstocks and technologies (pyrolysis) that increase the energy potential of these products. Thus, the objective of this study was to produce pellets from coffee residues, evaluate their energy potential, pyrolyze the pellets via slow pyrolysis and characterize the final products of the process (bio-oil and biochar). The pellets were produced from coffee husks in a pelletizer; some of the pellets were used for the combustion test, and others were used in the slow pyrolysis process. The efficiency in compacting the bulk biomass to obtain solid fuels was demonstrated by calculating the energy density. The pellet formation efficiency was also evaluated using stereoscopic images. Slow pyrolysis was performed at three final temperatures: 400 °C, 450 °C and 500 °C; the final residence time was 1 h. The product yields were calculated at the end of the pyrolysis process. The chemical compounds present in the bio-oil were identified by gas chromatography mass spectrometry (GC–MS), and the proximate analysis, higher heating values and Fourier transform infrared spectroscopy (FTIR) of the biochar were determined. The results showed that the prior addition of water to the coffee husk particles resulted in unstable pellets. The energy density of the pellets was statistically higher than that of the coffee husk. The combustion test allowed the combustion profile of the pellets to be determined, in which high temperatures and uniform burning were obtained. The pyrolysis product yields were influenced by the process final temperature. The biochar yield decreased with increasing temperatures; however, the fixed carbon and calorific values of the biochar collected at 450 °C were higher than the values of the biochar collected at other temperatures. The maximum yield of bio-oil was obtained at 450 °C, while the gas yields were the highest at 500 °C. The bio-oils obtained by higher pyrolysis temperatures comprised greater amounts of phenolic (phenol, phenol, 2-methyl- and phenol, 3-methyl-) and nitrogenous (caffeine) compounds. Lower temperatures yielded more esters (hexanedioic acid and bis(2-ethylhexyl) ester). The low atomic ratios H/C and O/C proved that temperatures ≥ 400 °C made the biochar more aromatic and carbonaceous, this fact was evidenced by the FTIR analysis. It is concluded that the coffee husk pelletizing process is a convenient alternative to obtain higher energy efficiency. Furthermore, from the energetic properties of the biochar the coffee husk has the potential to be used as fuel. [ABSTRACT FROM AUTHOR]

• Role of organic and inorganic nanoparticles in biohydrogen production was discussed. • Role of nanoparticles on pretreatment of various feedstocks were reviewed. • Nanoparticle in bioreactor design and biomass transformation was assessed. • Mechanistic role of nanoparticles in biohydrogen production was critically analysed. • Possible ways to improve biohydrogen yield through nanoparticle was defined. Sudden erratic climate change due to fossil fuel combustion and a steady rise in the oil price have engaged researchers in a race to develop sustainable and economically viable fuel i.e. biofuel. Among the biofuels, biohydrogen is considered to be the most efficient and the cleanest form of energy owing to its advantages of no adverse greenhouse gas emissions and the potential to be generated from various waste biomass or feedstocks. However, the biohydrogen production through photobiological and dark fermentation techniques has often suffered from lower yield, which is considered to be a major obstacle for commercial production. Nanotechnology stands out with a promising potential for the improvement of biohydrogen production owing to its precise structural and physiochemical properties. This review provides an insight into the development of various strategies (technologies) to improve biohydrogen production using organic and inorganic nanomaterials. Initially, a systematic evaluation of the nanomaterials in biomass transformation and an elaboration on the current status of nanomaterial applications in biohydrogen production, have been addressed. The review extensively compiles and describes the use of both organic and inorganic nanoscale materials in various fermentation processes. This is followed by the advancements made in the field of nanocatalysts for improved biohydrogen production along with the possible mechanisms involved in the biotransformation of feedstocks into hydrogen production by various microbial biorefineries. Additionally, the efficiency of nanomaterials in bioreactor designing to maximize biohydrogen has been discussed. The future perspectives on the applications of nanomaterials in improving biohydrogen yield have also been discussed. [ABSTRACT FROM AUTHOR]

• A novel biorefinery approach was explored to produce hythane from ethanol stillage. • Ideal hythane ratio of 0.29 was successfully obtained in two-stage AD of stillage. • Higher carbon conversion efficiency (75%) validated the efficacy of integration. • Energy analysis (EROI) assured the practical feasibility of the proposed method. • Biochar produced from digested almond shells exhibited agronomic properties. The present study is based on "waste to energy" concept, wherein the potential of almond crop residues viz., almond shells were investigated for biofuel production via different bioprocesses. Three routes, namely A1 representing hythane production through two-stage anaerobic digestion (TSAD), A2 representing ethanolic fermentation and A3 representing coupled ethanol and hythane production were evaluated for maximizing energy recovery. Results showed that in route A1, increased H 2 /(H 2 + CH 4) ratio (0.53) resulted in inappropriate hythane composition which was attributed to higher hydrogen yield of 236.6 L/kg chemical oxygen demand removed (COD r) and lower methane production (203.9 L/kg COD r) in the respective route. In route A2, sole ethanol production led to much lower carbon conversion efficiency (25.7%) and energy yield (6173.1 kJ/kg COD r) that questions the feasibility and efficiency of this process. However, in route A3, coupled ethanol and hythane production led to increased substrate degradation (91.3%) and higher carbon conversion efficiency (75.1%) resulting in enhanced energy recovery (22156.6 kJ/kg COD r) as compared to A1 route (13573.6 kJ/kg COD r). The stable H 2 /(H 2 + CH 4) ratio of 0.29 obtained in route A3 makes this pathway most suitable for efficient co-production of both biofuels. Further, linking of biochemical conversion process with thermochemical process viz., pyrolysis to produce biochar from almond shell residue, could be seen as an effective strategy for waste management and for enhancing the economic viability of the process. [ABSTRACT FROM AUTHOR]

• Production of biochar is a cost-effective route to capture atmospheric carbon. • Biochar has abundant physical and chemical properties. • Biochar properties are determined by feedstock type and production method. • Biochar are used to amend bioprocessing for production of biofuel and chemicals. • Biochar-based catalysts are efficient in syngas upgrading and biodiesel synthesis. Biochar is traditionally used to improve soil properties in arable land and as adsorbent or precursor of activated carbon in wastewater treatment. Recent advances have shown biochar potentials in enhancing productions of biofuels and chemicals such as bio-ethanol, butanol, methane, hydrogen, bio-diesel, hydrocarbons and carboxylic acids. The properties of biochar such as high levels of porosity, functional groups, cation exchange capacity, pH buffering capacity, electron conductivity, and macro-/micro- nutrients (Na, K, Ca, Mg, P, S, Fe, etc.) provide appropriate conditions to relieve physicochemical stresses on microorganisms through pH buffering, detoxification, nutrients supply, serving as electron carrier and supportive microbial habitats. This paper critically reviewed biochar production and characteristics, biochar utilization in anaerobic digestion, composting, microbial fermentation, hydrolysate detoxification, catalysis in biomass refinery and biodiesel synthesis. This review provides novel vision of biochar application, which could guide future research towards cleaner and more economic production of renewable fuels and bio-based chemicals. [ABSTRACT FROM AUTHOR]