Torrefaction of Lignocellulosic Biomass: A Pathway to Renewable Energy, Circular Economy, and Sustainable Agriculture

Abstract

Torrefaction, a mild thermochemical pretreatment process, is widely acknowledged as an effective strategy for enhancing the energy potential of lignocellulosic biomass. This review systematically evaluates the technological, environmental, and economic dimensions of lignocellulosic biomass torrefaction with the objective of clarifying its critical role in sustainable energy production and circular economy frameworks. Drawing from recent literature, the review covers process fundamentals, feedstock characteristics and operational parameters—typically 200–300 °C, heating rates below 50 °C per minute, ~1 h residence time, and oxygen-deficient conditions. The impacts of torrefaction on fuel properties, such as increased energy density, improved grindability and pelletability, enhanced storage stability, and reduced microbial degradation are critically assessed along with its contribution to waste valorization and renewable energy conversion. Particular emphasis is placed on the application of torrefied biomass (biochar) in sustainable agriculture, where it can enhance nutrient retention, improve soil quality and promote long-term carbon sequestration. This review identifies an unresolved research gap in aligning large-scale techno-economic feasibility with environmental impacts, specifically concerning the high process energy requirements, emission mitigation and regulatory integration. Process optimization, reactor design and supportive policy frameworks are identified as key strategies that could significantly improve the economic viability and sustainability outcomes. Overall, torrefaction demonstrates substantial potential as a scalable pathway for converting waste agricultural and forest residues into carbon-neutral biofuels. By effectively linking biomass waste valorization with renewable energy production and sustainable agricultural practices, this review offers a practical route to reducing environmental impacts while supporting the broader objectives of the global circular economy.

1. Introduction

Lignocellulosic biomass is Earth’s most abundant organic and renewable resource, containing plant dry matter from agriculture, forestry and industrial residues. Lignocellulosic biomass is majorly composed of cellulose, hemicellulose, and lignin. It also contains lipids, proteins, various elemental substances and inorganic compounds. Depending on the source, the contents of the lignocellulosic material vary in their composition, cellulose (35–55%), hemicellulose (20–40%), and lignin (10–25%) [1,2]. Lignocellulosic biomass is a cost-effective feedstock, noncompetitive with food crops, and offers sustainable energy production in the form of second-generation biofuels and could be utilized as an alternative to fossil fuels [3,4,5,6]. Further, to improve national energy security, lignocellulosic biomass-based energy facilitates greenhouse gas emission mitigation and offers economic reinforcement for rural communities [7]. Though the estimated global biomass production is 181.5 billion tons, only 8.5 billion tons are currently used, which shows huge potential towards biofuel production [8].

Traditionally, lignocellulosic biomass is utilized in cooking, heating, manufacturing, and construction purposes, whereas energy products and biofuels could be generated by thermochemical conversions (combustion, gasification, liquefaction, and pyrolysis) or biochemical conversions, microbial/enzymatic breakdown such as anaerobic digestion, fermentation, and other bioprocessing approaches [7,9,10]. Torrefaction is a thermochemical conversion technology usually operating at moderate temperatures (200–300 °C), which alters the biomass properties by improving energy density and reducing moisture content, making it apt for energy production. Torrefaction is an endothermal process, which results in enhanced calorific value, easier handling, storage conditions, and smooth transportation of biomass [11,12,13,14,15].

Lignocellulosic biomass is recognized as a vital bioenergy source due to its renewable nature, its capacity to reduce fossil fuel dependence and its potential for greenhouse gas (GHG) mitigation. Globally, in many developing regions, biomass already accounts for up to 35% energy use, mainly in cooking and heating [16]. Converting agricultural residues into energy resource supports concepts of the circular economy, by closing the material loops and improving resource efficiency [17]. This framework supports the regeneration of resources, recycling, and generation of value-added biomass streams, thus enhancing sustainability and systemic resilience [18]. This integration of biomass valorization with sustainable agriculture provides some economic incentives to farmers through the utilization of residual streams [19]. The significance of torrefaction in biomass valorization, bioenergy production, and sustainable agriculture, closely aligns with the United Nation’s Sustainable Developmental Goals (SDGs)—SDG 7 affordable and clean energy—bioenergy generation, SDG 12 Responsible consumption and production—circular resource management, SDG13 Climate action—reduction in GHG emissions and SDG 2 Zero hunger—enhancing sustainable agriculture and reducing environmental degradation.

Compared to the previous reviews on lignocellulose biomass torrefaction, the novelty of this work lies in its focus on an integrated analysis of three pillars—renewable energy, sustainable agriculture, and the circular economy—as an interconnected system, rather than addressing them separately as in earlier reviews. The principal contribution of this manuscript is its integrative focus on torrefaction as a bridge between agricultural waste valorization, renewable energy production, sustainable agriculture practices and circular economy models. While other recent investigations mainly focus on process engineering, energy yields, and environmental impacts of torrefaction [15,20,21,22,23,24,25,26,27], this review uniquely links its role across multiple systems via cross-sector integration. It evaluates how torrefied biomass can transform agricultural residues into valuable industrial inputs, enhance soil fertility and carbon sequestration in sustainable agriculture, and support scalable decarbonization in circular economy frameworks. Additionally, this manuscript evaluates the current techno-economic and environmental challenges, highlighting optimization strategies including life cycle assessment (LCA), which are rarely addressed in previous similar reviews. This perspective offers interconnected solutions to the emerging demands of climate-smart agriculture, waste management, and energy transition.

This review focuses on studies published between 2020 and 2025, identified through searches in Web of Science, Scopus, and Google scholar within the contexts of lignocellulosic biomass, environmental science, renewable energy and sustainable agriculture. The search strategy includes a combination of keywords such as lignocellulose, biomass valorization, torrefaction, renewable energy, sustainable agriculture, process integration, life cycle assessment, and feedstock availability using Boolean operators (AND, OR). Publications in languages other than English and non-peer-reviewed sources—including torrefaction technical reports, webpages and other forms of gray literature—were excluded. However, in Section 3 on Lignocellulosic Biomass Resource-Feedstock Distribution, selected official reports were included to provide a clearer understanding of the current situation. To describe the recent research trajectory of biomass torrefaction, we conducted a bibliometric analysis for the duration of 2014–2025 (treating 2025 as half a year). As per Web of Science and Scopus database responses, torrefaction research showed a consistent increase in the annual publications. The topic search includes the keywords “torrefaction”, “torrefied biomass”, “biomass pretreatment”, and “mild pyrolysis”. The majority of the torrefaction projects are led by China, USA, Canada, Malaysia, and Taiwan. Bibliometric analysis provides insights into term co-occurrence patterns, showing a recent shift from technical process parameters towards sustainability and supply chain integration.

2. Fundamentals of Torrefaction

Torrefaction is a mild pyrolysis, thermochemical process at a temperature range of 200–300 °C, which involves biomass heating in various heating processes [28,29]. Depending on torrefaction conditions, biomass fuel properties vary. The main parameters controlling the torrefaction process efficiency and the resulting biomass fuel properties are the temperature, pressure, residence time (duration), atmosphere, biomass particle size, and the specific area [15]. In

Table 1. Torrefaction fundamentals: typical operating conditions and product characteristics.

Parameters	Normal Range/Value	Effects/Remarks	References
Temperature range	200–300 °C	Optimal temperature range for mild pyrolysis or torrefaction. High temperature increases carbon content, reduces solid yield.	[30]
Residence time	10–90 min	Longer residence time increases devolatilization and improves calorific value	[31]
Atmosphere	Inert (N2, Ar, CO) or limited O2	Inert atmosphere prevents combustion, and higher solid yield. Limited O2 leads to partial oxidation.	[32]
Heating rate	<50 °C/min	Low heating rate enables uniform heating.	[33]
Calorific value (HHV)	18–24 MJ/Kg	Torrefied biomass yields higher heating value than raw biomass.	[34]
Energy yield	~50–80%	Represents a balance between energy density gain and mass loss. Energy yield decreases with increasing temperature and time.	[35]
Solid yield	60–80 wt% (dry torrefaction) 10–98 wt%	Solid yield is reduced with severity of torrefaction.	[36]
Solid products	Biocoal/biochar	Increased hydrophobicity, energy density, grindability.	[36,37]
Condensable products	water, organics (acid, alcohols, ketones, aldehydes, sugars)	Downstream processing for potential uses.	[38]
Non-condensable gases	CO2, CO, CH4, H2	Energy recovery systems.	[39]

HHV—higher heating value.

, we summarize the key torrefaction parameters along with their typical operating conditions and corresponding product characteristics [30,31,32,33,34,35,36,37,38,39]. Usually, an inert or low oxygen environment is maintained to enable thermal degradation without combustion. Oxidative torrefaction exhibits higher efficiency, shorter pretreatment time, and a low energy requirement [22], while longer residence times resulted in greater mass loss, but better fuel properties [23].

Depending on the atmosphere and moisture content, the torrefaction process can be classified into three types: dry (oxidative or inert atmosphere), wet (high moisture content), and steam (saturated or overheated steam) torrefaction [40,41,42,43,44]. In

Table 2. Comparison of various torrefaction techniques.

Torrefaction Method	Operating Conditions	Fuel Properties	Process Information	Suitability	References
Wet torrefaction (HTC)	160–250 °C aqueous or slurry	Uniform heating; improved ash; hydrophobic char after drying	Dewatering/drying step; effluent management required	High moisture/slurry feed stocks	[25]
Dry inert	200–300 °C N2, Ar	High HHV, hydrophobic, grindable, mass yield falls with severity	Mature and widely piloted; drying/heating integration is required	Co-firing pretreatment; pellatization feed	[25]
Dry oxidative	200–300 °C Controlled O2	Faster kinetics; excessive O2; partial oxidation; lower solid and C yield.	Does not require inert gas; potential auto thermal operation, need tight O2 control	When N2 supply is expensive/limited; quick pretreatment before gasification/combustion	[43]
Microwave assisted torrefaction (MAT)	200–300 °C Microwave heating	Fast HHV; lab studies; tunable volatiles and high solid yields	Scale-up limited by field uniformity, CAPEX for microwave systems	Decentralized, quick cycle pretreatments	[45]
Microwave assisted HTC (MAHTC)	HTC with microwave heating	Faster process, char suitable for power	Reactor design and penetration depth challenge at scale-up	Regions with low carbon electricity; effluent treatment	[46]

HHV—higher heating value.

, we present the characteristics of different types of torrefaction reactions, including their operating conditions, torrefied biomass fuel properties, process details, and suitability of various feedstock types. Based on the operating temperature used, torrefaction is categorized as mild (210–235 °C), medium (235–275 °C), and severe (275–300 °C) [11,23]. Torrefaction reaction has 5 operating stages with varying temperature based on the processes—initial heating (biomass drying from room temperature to 105 °C, moisture removal), pre-drying (105–200 °C, remaining moisture removal and biomass basic decomposition), drying and intermediate heating (~ 200 °C, release of physically bound water, biomass decomposition and devolatilization of organic compounds), torrefaction (starts at 200 °C remains at a constant temperature, highest mass loss), and cooling (200 °C to desired temperature, solid product) [14].

The key physiochemical changes that occur during the torrefaction reaction involve elemental distribution, composition variation, carbonization, depolymerization, dehydration (moisture reduction), devolatilization, deoxygenation, decarboxylation, and deacetylation [47,48]. Wood torrefaction investigations by Prins et al. [28] tested various wood biomasses focusing on weight loss kinetics and their fuel properties like heating value, moisture content, and energy density. In Figure 1, a schematic representation of lignocellulosic biomass torrefaction and its possible products are presented. As shown in the figure, during torrefaction, three main product streams are generated: (i) solid products (biocoal or biochar), (ii) condensable volatiles (moisture, bio oils, sugars, lipids, acids, aldehydes, alcohols, ketones, and oxygenates), and (iii) non-condensable gases (carbon monoxide, carbon dioxide, hydrogen, and methane) [47,48]. This leads to property changes, decomposition or degradation of cellulose, hemicellulose, and lignin causing the formation of chromophoric groups and increased carbonyl groups and thus, enhances the heating value of the biomass leading to better energy yield [49]. Hemicellulose degrades at lower temperatures (~220–315 °C), followed by cellulose (~315–400 °C), while lignin degrades over a broader temperature range of ≈160–900 °C. This thermal behavior explains why torrefaction primarily affects hemicellulose [50]. Pretreatment of lignocellulosic biomass is carried out to disintegrate the complex lignocellulosic components, thereby facilitating further downstream processes. After pretreatment, biomass undergoes saccharification, typically through enzymatic or acidic hydrolysis, to convert polysaccharides to monomeric sugars. These sugars are then fermented into biofuels such as bioethanol, biodiesel, or biobutanol. Finally the crude fermentation products are purified by distillation to obtain biofuels suitable for energy applications [51].

During torrefaction, hemicellulose undergoes devolatilization and carbonization, while cellulose and lignin primarily experience devolatilization and depolymerization. The release of volatile compounds through devolatilization reduces oxygen and increases relative carbon content, thereby enhancing calorific value [29,52]. As complex polymers, such as hemicellulose, break down into simpler molecules, biomass energy density, hydrophobicity, and grindability improve, while 75–95% of original energy content is retained [53]. Carbonization further increases the carbon content and decreases oxygen and hydrogen content, lowering the O/C and H/C ratios, which is suitable for the energy carrier [49,54]. Depending on feedstock type and operating parameters, torrefied biomass reported a mass yield of 42–91% and an energy yield of 61–89%. Overall, the thermochemical modifications during torrefaction improve key fuel properties, including energy density, calorific value, pelletization potential, grindability, hydrophobicity, and durability [29,49,55].

3. Lignocellulosic Biomass Resource-Feedstock Distribution

3.1. Availability of Biomass Feedstock

Biomass feedstock availability depends on ecological conditions, geographical locations, economic factors, regional production conditions, and export-import possibilities [56]. According to the Energy Progress Report 2025, Sustainable Development Goal 7.3 (SG 7.3) aims to double the energy intensity by 2030 compared to the 1990–2010 average. The selection of suitable and efficient renewable energy sources for electricity generation can significantly contribute to achieving this target [57,58]. The International Renewable Energy Agency (IRENA) analysis projects that the annual global sustainable biomass availability will expand to 535 million tons (Mt.) by 2050. As per the Planned Energy Scenario, the overall share of modern uses of renewables in total final energy consumption (TFEC) would grow to 23% in 2030 [57,59]. In accordance with international biomass supply assessments, global biomass production is estimated to be 2.13 billion dry metric tons in 2030, with an increase in ~60% compared to 2024 values. The current estimates project that the Americas lead production at 1.18 followed by Europe 0.91, Asia 0.52 and Africa 0.22 billion dry metric tons of biomass. Brazil and The United States (US) are the largest global produces, with sugarcane as the major feedstock in Brazil and corn starch and soybean oil in the US. In Brazil and the US, crop resources are used for ethanol and biodiesel production, and the bagasse and wood resources are used for energy generation. In Europe, lipid-rich crops are used for biodiesel production, with forest residues also contributing to biomass feedstock [60]. Ensuring sustainable biomass availability requires conscious efforts of balancing to avoid the over exploitation of natural resources or ecosystems; where biodiversity conservation, fair land access between energy-food crops and responsible water resource management have to be considered. Finally, the viability of biomass supply relies on identifying the appropriate energy conversion technologies and addressing the logistic hurdles in feedstock collection and transportation [33,61,62].

3.2. Lignocellulosic Biomass Supply in Europe and Worldwide

The key factors affecting the lignocellulosic biomass supply include the availability of resources, sustainability criteria, policies and regulations, economic and market factors, land use competitions, weather patterns, and technological feasibility. Lignocellulosic biomass contributes to 82% of Earth’s biomass where ~181.5 billion tons of lignocellulosic biomass is cultivated annually. From that, only 8.2 billion is used for bioenergy or biomaterial production, leaving the majority unused [63]. When compared globally, the EU generates ~80–150 Mt cereal residues and ~11 Mt forestry residues annually, which is comparatively limited in scale. The economic evaluations indicate that introducing price-induced incentives could boost up the crop residue availability by only 8–13%, as most farmers have already optimized their harvesting practices sustainably [64,65].

EU policies and regulatory framework ensures the sustainable harvesting of the biomass to ensure the maintenance of soil fertility, carbon stocks, and biodiversity; this limits the land availability for energy crops [66]. The Renewable Energy Directive (REDII) waste management policies regulate the sustainable biomass management [67]. Similarly, Land use, land use change and forestry (LULUCF) Regulation EU/2018/841 [68]-ensures the reliability of forest biomass for energy production by the national energy and climate plans (NECPs). Also, implementing regulation EU2022/2448 [69], supported setting sustainability criteria for forest biomass utilization under the Renewable Energy Directive 2018/2001 [70] regulation [71,72,73,74,75].

The logistics and supply chain challenges are the following: distance between locations, infrastructure, biomass quantity and quality, and seasonal supply issues [56,76]. Pretreatment of the biomass enables easy transportation, whereas establishing logistical hubs supports a smooth collection process, essential in providing a continuous demand-based market supply [77]. Similarly, climate and weather variations linked to geographical location affect biomass yield and supply, while optimization models and algorithms could improve the supply chain [78,79]. Sustainable biomass supply depends on healthy production systems; as the EU reliance on biomass increases, policies must prioritize regeneration [67,80].

4. Lignocellulosic Biomass Torrefaction Impact on Society

The torrefaction of lignocellulosic biomass ensures waste valorization, renewable energy production, enhancement in sustainable agriculture practices, emission control, and carbon footprint reduction, and thus leads to a climate neutral society within circular economy principles, as shown in Figure 2. The figure highlights the integration of renewable energy, sustainable agriculture, and the circular economy—as an interconnected system, for a future climate neutral society.

Recent studies displaying the societal impacts of lignocellulosic biomass are listed in

Table 3. Societal impacts of lignocellulose biomass torrefaction and benefits.

Impact Area	Societal Benefits	References
Waste valorization	Transforming agricultural/forestry residues to value-added materials—e.g., biofuels, biochar, biocoal	[81]
Renewable energy	Improves fuel quality by increasing fuel energy density, hydrophobicity, grindability, combustion energy; cleaner energy with reduced CO2 emissions	[82]
Circular economy	Promotes resource recovery, waste utilization, near zero waste, sustainable product development.	[83]
Climate challenge mitigation	Creates low-carbon fuels, reduces GHG emissions, renewable energy production, and reduces reliance on fossil fuels.	[83]
Sustainable agriculture	Biochar improves for soil enhancement, water retention, nutrient cycling, and ensures long–term carbon sequestration.	[84]
Economic development	Enables commercialization of biofuels and bio products, supporting green circular economy.	[85]
Environmental protection	Mitigates pollution by burning biomass waste, lowering emissions, biomass valorization, and process parameter optimization	[86]

along with the relevant benefits [81,82,83,84,85,86].

4.1. Torrefied Biomass in Renewable Energy Systems

The torrefaction of lignocellulosic biomass improves the biomass quality for renewable energy production by transforming it to an energy dense fuel material, which is more manageable compared to the original form. The torrefaction process leads to structural changes in biomass, which modify the physical and chemical properties, including flexibility, grindability, quality of the gas and liquid products (syngas and bio-oil), etc., [34,36,87]. The optimization and modeling of the torrefaction process by machine learning and hybrid models can control the reaction parameters (gas composition, temperature, and time) accurately. Also, using gene expression programming, biomass properties could be optimized. Integrating torrefaction with other thermochemical reactions, such as pyrolysis and gasification can enhance the overall yield, bio-oil/biochar production and final product quality and circular resource use [87,88]. The evaluation of wet and dry biomass torrefaction by simulation studies is performed to optimize the pretreatment conditions for energy-dense fuel production [89]. The latest pretreatment methods, like plasma-assisted processing, enable more efficient bioconversion of the biomass [90]. Similarly, the utilization of eutectic solvents in combination with pretreatments improves the delignification process, and enhances the biomass conversion process efficiency and sustainability [91].

Torrefied lignocellulosic biomass contributes to providing renewable energy through fuel upgrading (higher energy density, improved stability), reducing downstream energy (less moisture, 70–90% less grinding energy, less transport and storage cost), and generating superior quality products (syngas, biocrude, bio-coal, bio char) [34,92,93]. Compared to other pretreatment methods, torrefaction is an economical method in fuel upgradation by standardizing varying lignocellulosic biomass at a lower operational cost and offers the valorization of waste biomass resources [94]. Still, integrated torrefaction systems are expensive due to the scalability and operational expenses leading to extended capital requirements [95].

Optimized process design utilized with heat recovery enables torrefaction to improve the thermal energy efficiency > 90%. Solar-based torrefaction is another sustainable energy-efficient system [34,96]. Torrefaction enables the decarbonization of energy systems and transforming low value biomass into better fuels, which also supports net zero energy transition and reduced emissions. The LCA analysis of higher biomass co-firing reported a significant reduction in greenhouse gases, not only CO₂, but also lower NOx and SOx emissions compared to coal alone. However, extreme torrefaction conditions can outweigh the emission mitigation benefits as higher energy is required for the process, which makes the overall process expensive [97].

In

Table 4. Torrefaction of lignocellulosic biomass for renewable energy.

Feedstock	Torrefaction Strategy and Conditions	Outcomes	Application	References
Wheat straw	Oxidative vs. inert torrefaction. 230–305 °C, 20–60 min	HHV increased 19.4 MJ/Kg. mass yield 44%, energy yield 62%, grindability improved.	Upgraded solid biofuel for co-firing.	[98]
Wheat straw	Inert torrefaction (N2) 220–280 °C, 10 min	Improved grindability and flowability at 280 °C	Improved fuel properties.	[99]
Miscanthus, wheat straw, willow	Dry torrefaction(N2) 220–300 °C, 60 min	Improved HHV	Cleaner co-firing fuel.	[100]
Miscanthus, hops, MSW, and blends	250–350 °C, 30–60 min	Improved HHV	Solid fuels with 88% less GHG emissions.	[101]
Rose oil waste, pine saw dust	Torrefaction prior to co-pelletization	Increased HHV, energy density, hydrophobicity. Mass yield 70–78%, energy yield 73–102%	Torrefied co-pellets.	[102]
Forest residues and wood chip residues	Torrefaction post-pelletization	Increased HHV mass yield 60–80%, energy yield 80–95%	Improved fuel quality without binders, better combustion.	[103]
Wheat straw	Chemically treated torrefaction; RSM optimization	HHV 25.05 MJ/Kg mass yield 60%	Process optimization to maximize densification.	[104]
Forest waste	Aspen plus® software V12.1 plant level simulation 225–275 °C, 20–60 min	Improved HHV, scale-up insights obtained.	Commercial level scale-up information obtained.	[96]
Mixed wood	Densification after torrefaction, process optimization	Improved pellet quality and gasification performance, syngas production	Pre-gasification upgrade.	[105]

, further studies of lignocellulosic biomass torrefaction for renewable energy applications with torrefaction strategy, conditions, outcomes, and applications are displayed [96,98,99,100,101,102,103,104,105].

A major advantage of torrefied fuel is its compatibility with existing energy infrastructure and power grids, as its coal-like features allow a smooth transition to renewable fuels with minimal alterations [106]. Tests across various co-firing scenarios proved that high substitution ratios of biomass can be obtained without reducing boiler efficiency and load [107]. To further improve the energy efficiency, the critical parameters to consider are feedstock consistency, moisture content, thermodynamic parameters, reactor designs, process control, catalysts requirement, and economic feasibility [108,109].

4.2. Torrefied Biomass Applications in Sustainable Agriculture

The torrefaction of lignocellulosic biomass has become a promising solution to sustainable agriculture by transforming waste to cleaner fuels and soil amendments. The process significantly reduces moisture content, yielding lighter, hydrophobic, higher energy bioproducts that are less biodegradable and easy to store and transport [12,23,110,111,112,113].

Agricultural waste management through torrefaction is a multifaceted process. With the increasing global population and expanding food requirements, agricultural production has expanded rapidly, with escalating amounts of waste. Hence, the disposal of agricultural waste has become a major environmental challenge, often involving open burning practices releasing greenhouse gases (GHG)—carbon dioxide, nitrous oxide, methane, etc.—or landfills and illegal garbage disposals contaminating the natural resources [114,115]. With the depleting fossil fuels and great demand for energy sources, easily available agricultural residues have proved to be an excellent sustainable feedstock for biofuels [110,116,117,118]. These are called second-generation biofuels as they are generated from agricultural wastes [23,119,120,121]. Lignocellulosic residues, such as sugarcane bagasse, pulp mill waste, rice and wheat straws have been used as feedstock in biobutanol production, while inedible oilseeds and rice bran have been used in biodiesel, bread waste in bioethanol, olive pits in biocomposites and corn stalks in biohydrogen productions. Similarly, beech wood, mango/banana peels, corn stover, and wheat chaff have been utilized in the low-cost production of itaconic acid, a key building block of biodegradable bio-based plastics [122]. Sustainable biofuels of low activation energy generated from grape marc and olive stones have validated the waste-to-energy practice successfully [116]. Thus, torrefaction and related biomass treatments can be utilized for energy production in countries where agriculture is the main occupation [114,119,123].

Biochar is a reliable fertilizer derived from the lignocellulosic biomass residue torrefaction as shown in Figure 3, and it is widely used for multiple applications in agriculture as listed in the schematic. This value-added, renewable, carbon-rich solid biomaterial improves the aeration and potency of soil [124,125]. With enhanced properties of surface area and porosity, it functions as a nutrient reservoir, where the bio-product avails soil nutrients and furnishes the microorganisms, ameliorating its fertility, with better activity in sandy soils than clayey soils [125,126,127,128]. During torrefaction, hemicellulose is decomposed to expose lignin, and thus enables the adsorption of nitrogen, potassium, phosphorous, and sulfur, leading to an improvement in nutrient availability, retention, plant growth, and thus, higher crop productivity [84,129,130]

The introduction of torrefied biomass-biochar to the soil shifts beneficial soil microbes towards organic metabolic pathways and thus, facilitates the soil fertility by nutrient cycling [131]. Additionally, its lower carbon footprint makes it a sustainable and environmentally friendly fertilizer. Biochar-based carbon sequestration, one of the negative energy technologies, is a promising approach to trap CO₂ from the atmosphere to function as a long-term carbon sink in the soil, increasing its C:N ratio [125,132,133]. Water and air quality in agricultural fields can be refined with its potential to curb greenhouse gases working under a closed carbon loop. Biochar offers agronomic benefits as a more stable, slow degrading carbon resource, compared to raw biomass [110,114,117]. Thus, the productivity of this nutrient recovery operation is significant for agriculture, as it reduces dependence on traditional chemical fertilizers [134,135]. In addition to carbon sequestration and climate change mitigation, biochar also contributes to soil conservation without endangering food security [136].

Among greenhouse gases, nitrous oxide (N₂O) is a major contributor, originating as a by-product or an intermediate of nitrification and denitrification processes, and accounting for up to 70% of global emissions. Researchers validate that soil amendment with biochar can drastically reduce N₂O release through its acid buffering and liming characteristics [137]. With an alkaline pH (>8), biochar neutralizes acidic soils, thereby decreasing the activity of N₂O reductase enzymes, improving the denitrifier performance and ultimately dropping N₂O production in soil. These are further supported by biochar’s ability to regulate the growth of nitrite and ammonia oxidizing soil bacteria, adsorb NO₃⁻ and NH₄⁺, increase soil aeration, enhance soil water dynamics and promote climate-resilient soil management. Although the effectiveness of biochar depends on soil type and moisture content, this carbon-efficient strategy improves the circularity of agricultural farming practices [126,138,139].

Soil quality improvement by the process of mulching the soil with crop residues and biochar has gained many advantages in agriculture through ongoing changes in physical and hydro-thermal properties [127,140]. Of these, soil temperature regulation and the prevention of soil erosion are extraordinary. This can protect the loam layer and avoid washing away during extreme climatic conditions. Surface mulching improves soil health by increasing organic carbon content, which boosts microbial growth. This also reduces water losses through evaporation, demonstrating enhanced crop production and improving the harvest index as proved in wheat, maize, and soybean [114,140]. Similarly, biochar application moderates soil temperature, by lowering it during the day and increasing at night, effectively reducing extreme changes [127].

Torrefied biochar, after going through continuous dehydration, devolatilization, and depolymerization, has proved efficient in soil remediation and amendment [125,126,127,134]. Both modified lignocellulosic biomass (physical/chemical treatments, improved surface area), and non-modified forms are used in environmental remediation to remove heavy metals and pesticides from soil and water [122,126]. As a result, nutrient leaching and run-off can be minimized. Biochar also helps in soil amelioration with its high alkaline pH and cation exchange capacity [126]. Use of agricultural wastes in torrefaction improves the structure of soil with minimum consumption and, biochar being a good soil conditioner, resulting in more suitable pH, and a better uptake of nitrogen and phosphorus [123,124]. Biochar addition to sandy soils allows decreased infiltration and hydraulic thermal conductivity, thus improving water capture capacities with a reduced loss in water run-off. The physical properties of soil also found to be improved with biochar introduction are as follows: structural stability, water retention capacity, soil bulk density, compression strength, and resilience [127,129,131]. Improved water retention in soil not only increases the crop productivity, but also requires less irrigation. However, the application of biochar should be analyzed thoroughly due to the differences in plant requirements [126].

Trouble-free logistics is another advantage of torrefied biomass. Bulk densities of biomass feedstock have raised huge challenges in handling, storage, and transportation, which led researchers to investigate various treatment processes [118]. Biomass supply chains are optimized by approaches named Geographic Information System and OPTIMASS [111,135], which enables pathway selection based on the data collection of agricultural waste sources and locations, thereby supporting least-cost strategy. Network efficiency also depends on biomass type, mode of transportation, and number of torrefaction steps. Portable Pelleting Machines combined with torrefaction have shown significant improvements in efficiency, economic feasibility, and emission reduction [135]. In addition, torrefied fuel pellets densified with castor bean cake have exemplified improved combustion properties [23]. Stable long-term storage techniques like silaging and briquetting are exploited in torrefied biomass samples [23,111,141]. Altogether, torrefaction reduces operational costs by lowering transportation volumes and increasing the energy density of organic matter, thereby supporting smooth and efficient logistics [23,111].

Torrefied biomass has demonstrated beneficial effects on various physiochemical soil parameters, including bulk density, soil porosity, nutrient content, microbial activity, infiltration rates, pH, cation exchange capacities, emission control, and water holding capacity. It provides trouble free logistics, contributing to sustainable agriculture while supporting food security [84,129,142]. Thus, torrefaction can mitigate the adverse effects of agricultural wastes by turning them into profitable and sustainable products actively supporting agriculture. Incorporating torrefied biomass into modern cultivation practices highlights a regenerative concept of agriculture, which nurtures the land by improving fertility and positive soil amendments, backup food security, which aligns with environmental responsibility and sustainability.

4.3. Role of Torrefied Biomass in Circular Economy

The role of torrefied lignocellulosic biomass in the circular economy deals with waste feedstock valorization, resource efficiency, industrial symbiosis models, and bio-based materials production. The waste-to-value added material concept of torrefaction makes it a prominent pretreatment method in the circular economy model. The use of biomass as a coal replacement with good energy efficiency with lower GHG emissions makes torrefied biomass contribute to waste management, emission mitigation, carbon neutral alternative fuel, and sustainable bioproducts [106].

Lignocellulosic biomass is a suitable resource for biorefineries, enabling biofuel and bioproducts generation with minimal waste production. The conversion of waste biomass to value added products is a sustainable transformation in industrial practice. Integrated biorefineries ensure the complete valorization of the biomass with zero waste generation [143,144,145]. The evaluation of residual lignocellulosic biomass utilization shows that torrefaction can result in a range of products including biofuels, platform molecules (ethanol, furfural, hydroxyl methyl furfural, and levulinic acid), biodiesel, biogas, bio-oil, syngas, hydrogen, biomass briquettes, torrefied biomass, pellets, activated carbon, nanomaterials, etc. Waste valorization efforts have focused on agricultural residues as the main feedstock for generating these products [145]. Similarly, other lignocellulosic waste valorization has also been achieved by utilizing paper sludge, spent coffee grounds, oil palm residues, wood biomass waste mixtures (spruce, birch, pine), microalgae, etc. [146,147,148]. In integrated systems, a closed-loop approach can be observed, where torrefied biomass serves as the feedstock for bioethanol production, while lignin residues are utilized for carbon material synthesis [149].

Torrefaction can foster industrial symbiosis by linking materials and energy across various downstream processes. The use of the waste stream flue gas for oxidative torrefaction, replacing the inert environment for torrefaction is a reuse mechanism aligned with the circularity of the process, enabling the near-to-zero waste energy system. The integration of multiple waste biomass inputs and diverse product outputs further reinforces the essence of the circular economy concept [148]. Moreover, combining biochemical and thermochemical pathways within torrefaction improves the resource efficiency, maximizes the product yield, and minimizes the process energy requirements [150].

From a circular economic perspective, torrefaction also enables the synthesis of high-value bio-based materials like green packaging from torrefied coffee residue with polylactide (PLA), a thermally stable biodegradable bioplastic from torrefied PLA/biomass composites and bioethanol from sugarcane biomass. Torrefied biomass has also been used in the production of green building materials for construction, biochar for heavy metals removal in water treatment systems, and functional materials, such as vanillin (from lignin) and nanocellulose [147,151,152,153,154,155].

The torrefaction process serves as a sustainable conversion hub within the circular economy framework for lignocellulosic biomass. By enabling industrial symbiosis, it integrates waste valorization, closed-loop resource flows, carbon capture, and economic feasibility, thereby facilitating the production of clean energy carriers and high-value bioproducts. As outlined in Section 4, this conversion pathway forms a mutually reinforcing loop: agricultural residue characterized in Section 4.1 is upgraded to torrefied fuels and biochar; returning biochar to fields (Section 4.2) enhances soil health and nutrient-use efficiency, sequesters carbon, and mitigates the open-field residue burning. As synthesized in Section 4.3 and illustrated in Figure 2, this multifaceted approach couples waste valorization and soil generation, and fossil fuel displacement closes material loops and advances climate-neutral energy systems.

5. Techno-Economic and Environmental Challenges

As a transformative technology for lignocellulosic biomass utilization, torrefaction deals with various techno-economic and environmental hurdles. Figure 4 explains the various steps involved in the techno-economic evaluations. The major technological challenges include reactor design, scale-up, the regulation of process parameters, and process optimization strategies. In large reactors, achieving a uniform temperature is often difficult and results in incomplete or over-processed biomass and reduced end product quality [24,34,156]. The source and composition of the biomass also influence torrefaction performance, as heterogeneity affects thermal degradation behavior and product stability [106]. Additional bottlenecks include process integration, parameter optimization, and scale-up. Commercial level implementation requires process stability, operational safety, and system reliability. Scaling up torrefaction from the laboratory to industry remains challenging due to the high capital and operating expenses (OPEX). Recent studies highlight that the production system-torrefaction reactor alone can account for the majority of the total capital investment [39]. The reactor design, installation, heat transfer limitations, reduced energy efficiency, and emission control are other concerning factors in scale-up [157]. The management of large volumes of reactive gases requires a safe and stable infrastructure. The condensation of bio oils and tars can cause system disruptions and increase maintenance needs [158]. When biomass is co-fired with coal, ash-related troubles, like slagging and fouling, remain, which is another hurdle [159,160]. Finally, as an energy-intensive process, improving overall energy efficiency remains the critical challenge.

The economic challenges include the high capital burden and operational costs. Among the integrated systems, the torrefaction reactor is one of the most expensive parts, which requires 25–34% of the total capital investment. Compared to traditional wood pellet plants, the torrefaction system requires a 55–75% higher investment. Also, commercialization challenges are faced due to the competitive cost of other resources (coal), which do not require much processing [39,161]. Operational costs are another parameter including the feedstock expense, energy requirement, and production cost. Compared to wood pellets, torrefaction systems use 33–43% more energy so, when wood pellets cost $126/metric ton, torrefied pellets cost in the range of $183–191 per metric ton [94,161]. The cost of torrefied biomass is often higher than coal, sometimes even higher than preprocessed biomass, thus, market integration of the torrefied products to the existing energy market with economic feasibility is another challenge [94].

Several techno-economic analyses present conflicting views on the economic viability of torrefaction for biomass valorization. High capital and operational costs, fluctuating feedstock prices, and scale-up uncertainties pose significant economic barriers. However, other studies highlight economic synergies in integrated biorefinery models, co-firing with coal, and leveraging by-products like biochar, to offset costs and improve returns. The biggest trade-off happens when maximizing energy yield and expanding the product range to achieve quicker profits. However, ensuring the long-term sustainability for diverse products requires intensive operational management [15,162,163].

The next barrier is environmental challenges, which include pollutant formation, emission control, energy requirements, safety and storage concerns, and sustainability of the biomass supply. The emission profile of torrefaction is strongly influenced by feedstock properties, process conditions, operating parameters and preprocessing steps such as solar drying [164,165,166]. Control of the GHG emissions is critical in climate change mitigation. Although torrefied biomass is often considered carbon neutral, the torrefaction process involves fuel combustion and thus generates emissions, specifically volatile organics. Due to the variable composition of these gases and lack of integrated capture systems, managing volatile and other non-condensable off gases remains a significant challenge. Existing process configurations often lack the real-time monitoring and adaptive control mechanisms, which compromises environmental compliance and operational safety [164]. Additionally, emission control strategies like advanced reactor designs and catalyst applications in other similar hydrothermal processes also remain underdeveloped [91]. To mitigate the environmental risk, these gases need to be reused or treated to prevent pollution [97]. Hence, advanced process control technologies, robust reactor design, and tailored capture technologies are required to regulate emissions and ensure sustainable torrefaction processes. The formation of persistent organic pollutants (polychlorinated dibenzo-p-dioxins and dibenzofurans), ash, and tar were reported during torrefaction. Similarly, safety concerns are higher as the torrefaction temperature rises, due to the self-heating and self-ignition nature of the process [134]. To ensure the sustainability of the entire torrefaction process from biomass resources, process conditions, energy input, emissions, and processing of volatiles and other end products, LCA analysis and modeling must be conducted [167].

6. Environmental Impacts and Life Cycle Assessment

To evaluate the potential of lignocellulosic biomass as a sustainable energy source, its environmental impacts and LCA are important. LCA helps to find the ecological footprint of biomass from production to disposal, portraying its positive and negative influences. LCA is critical in optimizing sustainable production strategies and reducing the environmental impact [168,169,170]. Being a renewable resource, lignocellulosic biomass substantially reduces the emissions of greenhouse gases compared with traditional fossil fuels [170,171,172,173]. Selecting the suitable production method, feedstock establishment, economic feasibility of production, mode of operation (batch, semi-batch, continuous), chemicals, solvents, etc., can result in varying energy requirements and environmental footprints [174]. For example, the LCA analysis of the wet torrefaction process on sugar cane bagasse utilizing LCA (ISO 14040/44) [175,176] Ecoinvent 3.0 database ReCiPe midpoint methodology analyzed a 3E feasibility approach, based on 5 environmental impact categories—climate change, freshwater eutrophication, freshwater ecotoxicity, human toxicity, and fossil depletion [46]. The microwave-assisted torrefaction MAHTC showed lower global warming potential (GWP) that coal-based electricity, still higher depletion observed use to the electricity use, and toxicity driven by combustion emissions. The challenges involved in the study are the requirement of high electricity for heating, management of the liquid effluent, resource allocation, and evaluation of the combustion emission profile. The mitigation strategies include heat integration like the use of natural gas or waste heat for preheating and microwave liquid recovery or reuse plans, and strict emission controls towards flue gas. Further recent LCA evaluations with LCA tools, GWP values, and challenges with mitigation plans are listed in

Table 5. LCA of lignocellulosic biomass torrefaction.

Feedstock and Process	LCA Software/ Method	LCA Numeric Highlights	Hotspots/Challenges	Mitigation Plans	References
Corn stalk; torrefied pellets for heating	LCA with 5 stages—biomass collection to combustion heating; CML, IPCC 100a.	High net energy output/input ratio, positive energy balance, increased fuel energy and greenhouse gas reduction (85–95% less emission); total GWP = 175.806 kg CO2 eq	Upstream farming inputs; dominate energy use.	Improve end use efficiency; transparently apply system expansion/credits; reduce fertilizer intensity/logistic energy	[177]
Residual wood and wood chips; co-fired with coal after torrefaction; dry torrefaction	SimaPro; IPCC 2021, and GWP 20. LCA biomass harvesting, torrefaction, pelletization processes, and CO2 emissions.	Manufacturing emissions at 270 °C; 0.01423 wood chips and 0.04207 kg CO2 eq/day vs. 100% coal; 270 °C optimal; 310 °C degrade benefits	Drying energy, low mass yield at high severity; logistics; higher co-firing ratio, greater proportion of coal replacement.	Target 230–270 °C; maximize co-firing within boiler limits; cut drying energy; site near feedstock	[97]
Corncob; dry torrefaction	openLCA 1.10.3. software, ecoinvent 3.4 with CML2001: cradle-to-gate approach	Lowest impact at 200 °C; optimal trade-off 250 °C (upgrade vs. impact)	High severity ≥ 250 °C improves energy density; process energy	Prefer light-mild severity; process heat recovery; meet fuel specs with minimal energy	[178]
British Columbia torrefied wood pellets	GHGenius database ((S&T)2 Consultants Inc. 2017) Ecoinvent database. Cradle-to-gate (harvest to pellet product) values environmental, energetic, and economic (3E) metrics.	≥85% GHG reduction vs. coal at endues; supply chain emission offset; ≤15% savings. Great for overseas market (shipping logistics); torrefied pellets required 85% less energy than original biomass.	Transport and drying major contributor; reduction cost and carbon price	Low carbon drying, optimize rail/ship logistics; prioritize coal displacement; policy support for cost gap	[179]
Microalgal biomass Chlorella vulgaris; torrefaction (severity index); up-scaling	Simapro 8.5.2 LCA software with Ecoinvent database. Environmental impact analysis of the production to torrefied biomass	GWP falls by 128% (open pond) and 91% (PBR) on scale-up; net-negative GWP achievable at pilot-scale open pond (biogenic uptake)	Cultivation energy dominated; severity (temperature) drives GWP more	Favor open ponds weather feasible; scale-up; minimize electricity; optimize severity	[180]
Mustard straw; dry torrefaction	SimaPro V 9.1 software with Eco-invent version 3. ReCiPe 2016 Midpoint (H) method cradle-to-gate approach.	Directional; impact of increased rise in temperature; Main factor contributing to emission-transportation.	Transport distance; high severity energy demand	Site plant close to fields; mild severity; valorize vapors for drying	[181]
Coconut and rice husk co-firing with coal	SimaPro 9.5.0.0 Ecoinvent 3.9; ReCiPe 2016 with cradle-to-grave approach	Coal highest acidification 164.08 Kg SO2 eq and eutrophication 8.82 Kg SO2 eq; Biomass blends and reduced emissions	Transport distances; coal biomass ratio optimization	Higher biomass ratio; optimized logistics; promote sustainable and circular energy blends	[182]
Chinese medicine residue microwave assisted torrefaction	Open LCA v2.4.1 with eco-invent 3.4 and CML 2001; cradle-to-grave approach	First LCA analysis on this residue; GWP value 0.01–0.08 kg CO2 eq less than conventional torrefaction; acidification potential 9.45 × 10−6−6.78 × 10−5 (kg SO2 eq)	Emission composition; new feedstock uncertainties; heat regulation	Tailored emission control; integrate heat regulation	[183]
Rice straw; Dry torrefaction (inert N2)	openLCA; eco-invent 3.4. ReCiPe, and CML2001 (multi end-point impact category)	Impact displayed positive correlation with torrefaction temperature; light-mild severity; GWP- 0.1469–0.2707 kg CO2/1 Kg rice straw	Process severity; heat input for torrefaction	Operate at mild severity (200–250 °C); integrate heat recovery	[184]

GWP—global warming potential; PBR—photobioreactor; MAHTC—microwave-assisted hydrothermal carbonization. Functional units and boundaries are reported exactly as in the original studies; no cross normalization was applied. Consequently, comparisons across rows are primarily qualitative.

[97,177,178,179,180,181,182,183,184].

7. Future Research Directions

Lignocellulosic biomass represents a promising and sustainable source of bioenergy. To improve the sustainability of torrefaction, further technological developments are essential. Advanced reactor designs that address scale-up challenges and optimize heat transfer parameters such as heat rate regulation, uniform heat distribution, and heat loss prevention could improve the energy efficiency and thus, the total cost of production [185]. Integrated biomass with CO₂ capture-torrefaction systems presents an excellent option to reduce emissions; similar technology could be utilized for other gaseous emissions to prevent their environmental release [186]. Solar-driven torrefaction (Solar-T) offers another strategy to reduce the energy requirements while creating more transportable biofuels, showing excellent future potential [187]. Similarly, hybrid systems that integrate oxidative-inert torrefaction, or utilize flue gas and CO₂ could improve the torrefaction efficiency [96]. Process optimization through modeling and machine learning can also enhance the process and product quality [188]. Additionally, robust safety protocols are required for the safe handling and storage of the torrefaction end-products and emissions to prevent pollution and associated environmental impact [134].

Despite these advances, several critical gaps require further studies to establish the environmental sustainability and long-term viability of torrefaction. At first, the lack of standardized, large-scale LCAs—with inconsistencies in system boundaries and treatments of off gases—limits comparability and reliability across studies [177]. Second, the characterizations and control process emissions remained underdeveloped due to the variable composition of volatile gases and other by-products, which limits the effective emission capture [148]. Third, many techno-economic analyses rely on assumed parameters, without considering the uncertainties in feedstock supply and energy expense, which constrains the long-term viability [95]. Additionally, the scarcity of data demonstration systems hinders the robust evaluation of system reliability, maintenance, and environmental performance under real operating conditions [189].

Future economic improvement strategies should focus on production capacity improvement to reduce the overall cost, integration or modification of the current facility to reduce initial capital expense and implementing supportive policies or subsidies such as renewable energy credits and carbon pricing [161]. Ultimately, integrated systems combining the LCA and techno-economic analysis across various process pathways and feedstock logistics are required to determine the optimal conditions of sustainable torrefaction [97,190].

8. Conclusions

This review evaluates the recent advances (2020–2025) in torrefaction of lignocellulosic biomass into high value biofuels and other bioproducts. The core research question addressed was the extent to which torrefaction enables energy system decarbonization and circular bioeconomy outcomes, particularly when integrated with biorefinery pathways, and under which process and supply chain conditions it becomes environmentally and economically preferable to alternatives.

Torrefaction improves fuel quality by enhancing calorific value, reducing moisture content, and increasing carbon concentration. Beyond energy applications, torrefaction-driven biomass valorization supports sustainable waste management through the production of bioplastics, nanocellulose-activated carbon nanomaterials, and biochemicals, while biochar contributes significantly to soil health, nutrient retention, and carbon sequestration in agriculture [191,192].

The decarbonization potential of torrefied biomass is dependent on system boundaries and co-firing ratios. Life cycle assessments show that co-firing torrefied pelletized biomass with coal can significantly reduce overall CO₂ emissions, with mitigation increasing at higher biomass shares. However, benefits vary with torrefaction severity, pelletization energy requirements, transport distances, and the accounting of biogenic carbon. An operating temperature of 270 °C has been identified as an optimal balance between energy yield and emissions, where more severe treatments can risk overall gains through excessive mass loss [97].

Advances in standards and fuel quality are critical for commercialization. ISO 17225-8:2023 [193] provides graded specifications for thermally treated, densified biofuels across multiple feedstock, improving interoperability with combustion systems, increasing financing confidence and regulatory permitting [194]. Process integration offers additional benefits: microwave assisted torrefaction and torrefaction-pyrolysis integration demonstrate a higher yield and lower emissions at lab/pilot scales; however, long-run continuous large-scale validations remain lacking [45]. Techno-economic feasibility depends on feedstock type and configuration, with reactor CAPEX and operational energy dominating the costs [195].

At the system level, feedstock availability and location constrain sustainable biomass supply which limits the amount of sustainably sourced biomass, which can be co fired to reduce emissions. For mitigating, significant emission reductions may require coupling torrefaction with Carbon Capture Storage (CCS) or Bioenergy with CCS (BECCS), supported by strong feedstock management to reduce land-use change [196,197]. Current research on torrefaction remains limited by inconsistent LCA assumptions, small scale focus, feedstock variability, and supply chain challenges. Addressing these limitations through harmonized LCAs, pilot-to-large-scale validations, advanced modeling, and improved feedback governance is essential to establish torrefaction as a commercially viable decarbonization pathway.

Greater emphasis is required on integrating torrefaction with CCS/BECCS and advanced biorefinery systems to unlock net negative emission pathways. Ultimately, torrefaction offers a multi-faceted opportunity to decarbonize energy systems, supporting sustainable agriculture, and advancing circular economy models, when deployed under technical, economic, and governance conditions.