Due to increasing anthropogenic activities, especially industry and transport, the fossil fuel demand and consumption have increased proportionally, causing serious environmental issues. This ...attracted researchers and scientists to develop new alternative energy sources. Therefore, this review covers the biofuel production potential and challenges related to various feedstocks and advances in process technologies. It has been concluded that the biofuels such as biodiesel, ethanol, bio-oil, syngas, Fischer–Tropsch H2, and methane produced from crop plant residues, micro- and macroalgae and other biomass wastes using thermo-bio-chemical processes are an eco-friendly route for an energy source. Biofuels production and their uses in industries and transportation considerably minimize fossil fuel dependence. Literature analysis showed that biofuels generated from energy crops and microalgae could be the most efficient and attractive process. Recent progress in the field of biofuels using genetic engineering has larger perspectives in commercial-scale production. However, its large-scale production is still challenging; hence, to resolve this problem, it is essential to convert biomass in biofuels by developing novel technology to increase biofuel production to fulfil the current and future energy demand.
•Emerging technologies for biofuel production are reviewed.•Current and future biofuels' demands are studied.•Engineered bioprocesses for biofuels production from are revisited.•Biofuels are seen to have a huge commercial potential in the future.
Lignocellulosic biomass (LCB) is expected to play a significant role in achieving the goal of biomass-to-bioenergy conversion due to its wide distribution and low price. Acidogenic dark fermentation ...of LCB is a promising approach to the sustainable production of biohydrogen (bioH2) from this valuable substrate. Because of its inherent recalcitrance, LCB requires pretreatment to increase its digestibility and enable its improved utilization. Intense thermochemical pretreatments solubilize the lignin and hemicellulose and lead to the formation of a variety of inhibitory byproducts, such as short-chain carboxylic acids, furfural, 5-hydroxymethylfurfural (5-HMF), vanillin, and syringaldehyde, which interfere with the physiological and metabolic functions of dark fermentative microbiota, thus inhibiting bioH2 production. To offset the negative impacts of these inhibitors on bioH2 production, approaches to detoxify lignocellulosic hydrolysates have been considered. This review comprehensively discusses the generation of lignocellulosic inhibitory byproducts in commonly used, contemporary pretreatment regimens and their inhibitory effects on dark fermentative H2 production. Furthermore, the mechanisms of inhibiting H2 producing bacteria and their effects on bacterial community dynamics in mixed cultures are reviewed. State-of-the-art strategies for detoxifying pretreated LCB are discussed. The selection of desirable alternative lignocellulose pretreatment strategies that produce less or no inhibitory byproducts are highlighted. Finally, this review discusses the economic aspects of bioH2 production from LCB, considering the pretreatment and detoxification process. Given the limitations of previous studies, future research for developing cost-effective strategies to overcome byproduct inhibition during dark fermentation of pretreated LCB are suggested.
•The effects of lignocellulosic inhibitors on bioH2 production are discussed.•The mechanisms of action of inhibitors on bioH2-producing bacteria are elucidated.•The changes in H2-producing microbiota structure due to inhibitors are interpreted.•State-of-the-art strategies to mitigate problems caused by inhibition are reviewed.•In situ detoxification allows the removal of inhibitors during dark fermentation.
The dense structure of lignocellulosic biomass hinders efficient energy recovery from anaerobic digestion (AD). However, microorganisms or specific compounds can effectively break down ...lignocellulosic structure, increasing energy generation efficiency. Biogas slurry (BS) contains microorganisms and inorganic components that can act on lignocellulose. This study investigated the effects of BS on wheat straw (WS) pretreatment, focusing on key components such as ammonia nitrogen, acids, microorganisms, and metal ions in BS. To evaluate the mechanism, three-dimension excitation emission matrix (3D-EEM), fourier transform infrared spectrometer (FTIR), X-Ray diffraction (XRD), and lignocellulose composition analysis of were used. The effect of pretreatment on methane production was assessed using batch AD and the modified Gompertz model. Additionally, an economic analysis was conducted to compare different pretreatment methods. The results indicated that BS pretreatment significantly improved biodegradability (increased by 32.6 %), reduced crystallinity (by 24.6 %), and modified the composition of lignocellulose components. Furthermore, the abundance of hydrolysis and acidification bacteria, as well as acetoclastic methanogen, increased in the AD system after WS pretreatment with BS. Consequently, the methane production potential of WS increased by 23.8 %. Notably, ammonia nitrogen and microorganisms emerged as the primary active components in BS, exhibiting a synergistic reinforcing effect. This synergy significantly contributed to the breakdown of lignocellulose structure and improved the effectiveness of WS pretreatment. Moreover, the economic analysis demonstrated that BS pretreatment resulted in 33.2 % higher economic benefits compared to no pretreatment. These findings highlight the promising potential of BS pretreatment as a cost-effective and efficient strategy for improving biogas production from lignocellulosic biomass.
Display omitted
•A green pretreatment of straw method for methane production was proposed.•BS changed the biodegradability (+32.6 %) and crystallinity (-24.6 %) of straw.•Methane yield and benefit increased by 23.8 % and 33.2 % after pretreatment.•Microorganisms and ammonia were the key components for pretreatment.
Display omitted
•Lignocellulosic biomass is a clean energy source for biorefinery applications.•Pretreatment is a key step for biomass transformation to valuable chemicals.•Efficient and ecofriendly ...pretreatment approach to disintegrate biomass is needed.•Recent advances in physical and chemical pretreatment approaches are discussed.•Understanding of pretreatment mechanism is required for overcoming the challenges.
Depleting fossil reserves and growing energy needs have raised the demand for an alternative and clean energy source. The use of ubiquitously available lignocellulosic biomass for developing economic and eco-friendly large scale biorefinery applications has provided the much-needed impetus in this regard. The pretreatment process is a vital step for biomass transformation into added value products such as sugars, biofuels, etc. Different pretreatment approaches are employed to overcome the recalcitrance of lignocellulosic biomass and expedite its disintegration into individual components- cellulose, hemicellulose, and lignin. The conventional pretreatment methods lack sustainability and practicability for industrial scale up. The review encompasses the recent advances in selective physical and chemical pretreatment approaches such as milling, extrusion, microwave, ammonia fibre explosion, eutectic solvents etc. The study will allow a deeper understanding of these pretreatment processes and increase their scope as sustainable technologies for developing modern biorefineries.
Biochar is an ample source of organic carbon prepared by the thermal breakdown of biomass. Lignocellulosic biomass is a promising precursor for biochar production, and has several applications in ...various industries. In addition, biochar can be applied for environmental revitalization by reducing the negative impacts through intrinsic mechanisms. In addition to its environmentally friendly nature, biochar has several recyclable and inexpensive benefits. Nourishing and detoxification of the environment can be undertaken using biochar by different investigators on account of its excellent contaminant removal capacity. Studies have shown that biochar can be improved by activation to remove toxic pollutants. In general, biochar is produced by closed-loop systems; however, decentralized methods have been proven to be more efficient for increasing resource efficiency in view of circular bio-economy and lignocellulosic waste management. In the last decade, several studies have been conducted to reveal the unexplored potential and to understand the knowledge gaps in different biochar-based applications. However, there is still a crucial need for research to acquire sufficient data regarding biochar modification and management, the utilization of lignocellulosic biomass, and achieving a sustainable paradigm. The present review has been articulated to provide a summary of information on different aspects of biochar, such as production, characterization, modification for improvisation, issues, and remediation have been addressed.
Display omitted
•Emerging researches on toxic pollutants removal using biochar has been addressed.•Advanced techniques on biochar production have been articulated.•Obligated properties of biochar for environmental applications have been discussed.•Biochar amendments on ameliorating the soil fertility have been analyzed.•Crucial stumbling block for production and application of biochar were reported.
Display omitted
•Eluviation-illuviation in hydrothermal carbonization (HTC) affect hydrochar mineralogy.•Manure pellet (MP) hydrochar has low gross calorific values (GCV).•HTC temperature effect on ...GCV of MP hydrochars is negligible.•High ash content in MP impedes C recovery at HTC temperature above 180 °C.•HTC temperature drives GCV of hydrochars from lignocellulosic biomass.
The hydrothermal carbonization (HTC) process that converts wet/dry biomass to hydrochars (for use as solid fuels or adsorbents) needs to be optimized. We investigated the interactive effects of feedstock type and HTC temperature on chemical, fuel, and surface properties of hydrochars produced from lignocellulosic (canola straw, sawdust and wheat straw) and non-lignocellulosic feedstocks (manure pellet) at 180, 240 and 300 °C. Increased HTC temperature decreased hydrochar yield and surface functional group abundance, but increased hydrochar thermal stability due to increased devolatilization and carbonization. Hydrochar surface area ranged from 1.76 to 30.59 m2g−1, much lower than those of commercially available activated carbon. Lignocellulosic and non-lignocellulosic feedstocks were distinctly affected by HTC temperature due to variable carbonization from ashing. Hydrochars produced from lignocellulosic biomass at 240 and 300 °C resembled high-volatile bituminous coal. Hydrochars should be designed for specific applications such as fuels by selecting specific feedstock types and carbonization conditions.
Display omitted
•In-situ pyrolysis regulation and post-modification of biochar were summarized.•The relationship between physicochemical properties and applications of biochar was analyzed.•The ...future research requirements for biochar preparation and applications were proposed.
Biochar is a carbon-rich product obtained from the thermo-chemical conversion of biomass. Studying the evolution properties of biochar by in-situ modification or post-modification is of great significance for improving the utilisation value of lignocellulosic biomass. In this paper, the production methods of biochar are reviewed. The effects of the biomass feedstock characteristics, production processes, reaction conditions (temperature, heating rate, etc.) as well as in-situ activation, heteroatomic doping, and functional group modification on the physical and chemical properties of biochar are compared. Based on its unique physicochemical properties, recent research advances with respect to the use of biochar in pollutant adsorbents, catalysts, and energy storage are reviewed. The relationship between biochar structure and its application are also revealed. It is suggested that a more effective control of biochar structure and its corresponding properties should be further investigated to develop a variety of biochar for targeted applications.
Nanotechnology has become a revolutionary technique for improving the preliminary treatment of lignocellulosic biomass in the production of biofuels. Traditional methods of pre-treatment have ...encountered difficulties in effectively degrading the intricate lignocellulosic composition, thereby impeding the conversion of biomass into fermentable sugars. Nanotechnology has enabled the development of enzyme cascade processes that present a potential solution for addressing the limitations. The focus of this review article is to delve into the utilization of nanotechnology in the pretreatment of lignocellulosic biomass through enzyme cascade processes. The review commences with an analysis of the composition and structure of lignocellulosic biomass, followed by a discussion on the drawbacks associated with conventional pre-treatment techniques. The subsequent analysis explores the importance of efficient pre-treatment methods in the context of biofuel production. We thoroughly investigate the utilization of nanotechnology in the pre-treatment of enzyme cascades across three distinct sections. Nanomaterials for enzyme immobilization, enhanced enzyme stability and activity through nanotechnology, and nanocarriers for controlled enzyme delivery. Moreover, the techniques used to analyse nanomaterials and the interactions between enzymes and nanomaterials are introduced. This review emphasizes the significance of comprehending the mechanisms underlying the synergy between nanotechnology and enzymes establishing sustainable and environmentally friendly nanotechnology applications.
Display omitted
•Nanotechnology enhances biomass pre-treatment, overcoming traditional limitations.•Nanomaterials boost enzyme catalysis.•Engineered nanocarriers biological cascades, improving increase stability and efficiency.•Porous nanomaterials enhanced substrate transport, increasing catalytic efficiency.•Lignocellulosic biomass can be converted into valuable products.
•A review of supercritical water gasification of real biomass rather than model compounds.•The relationship between hydrogen yield and biomass type is elucidated.•The impact of all process variables, ...including the use of catalysts are quantified.•A technoeconomic study to show how the process could become viable through scale up.
Supercritical water gasification (SCWG) is a combined thermal decomposition and hydrolysis process for converting wet biomass feedstock with high water content potentially (80 wt%) to syngas. The process bypasses the need for an energy intensive pre-drying step and also needs relatively shorter residence times (of the order of seconds to minutes) when compared to conventional gasification. The main target of SCWG is to obtain syngas rich in hydrogen whilst minimising char formation. In recent years, SCWG studies have advanced from using model compounds (e.g. glucose and cellulose) towards the use of real biomass and its waste (e.g. sugarcane trash). The use of biomass as a feedstock creates real opportunities for the technology since it is available in some form, regardless of location. This review discusses the findings from SCWG studies that have used real biomass as a feedstock. The effects of reaction temperature, pressure, residence time and feedstock concentration to the hydrogen yields are presented. The relationship between the main components in biomass (cellulose, hemicellulose and lignin) and hydrogen yields are also discussed. Homogeneous and heterogeneous catalysts have been used to enhance SCWG with real biomass feedstock and the benefits of these approaches are also considered. The economic benefits of running the catalytic SCWG at 400 °C compared to non-catalytic operation at 600 °C is evaluated. Reactor configuration and process conditions vary across the literature, and various authors describe the associated challenges (char formation and plugging, corrosion) as well as promising solutions to tackle these key challenges.
•Deep eutectic solvent studies on biomass pretreatment have been reviewed.•Basics of DES fractionation of lignocellulosic biomass have been summarized.•Mechanisms of using DES for biomass ...fractionation have been discussed.•Prospects and challenges for future works have been outlined.
Biomass recalcitrance hinders efficient utilization of lignocellulosic biomass, making pretreatment process a crucial step for successful biorefinery process. Pretreatment processes have been developed for processing biomass, while technical obstacles including intensive energy requirement, high operational cost, equipment corrosions resulted from currently applied techniques promote the development of new pretreatment process for biomass. The deep eutectic solvent (DES) has been recognized as a promising solvent for biomass pretreatment, although the DES application toward biomass is still in its nascent stage. This review summarized the current researches using DES for biomass pretreatment, focusing particularly on lignin extraction and saccharification enhancement of lignocellulosic biomass. The mechanisms for biomass fractionation using DES as agents are introduced. Prospect and challenge were outlined.
