Decarbonizing hard-to-abate industrial sectors that require high-temperature process heat, notably steel and cement, demands renewable solid fuels with rigorously predictable properties. Hydrothermal carbonization (HTC) of biomass residues offers a promising route to such fuels, yet feedstock heterogeneity and process variability impede the reliable prediction of hydrochar properties and emissions reduction potential. Here, we introduce a machine learning framework leveraging a Mixture of Experts (MoEs) strategy to overcome these limitations. Our approach integrates clustering algorithms with tailored regression models and a gating network for autonomous model assignment, achieving superior accuracy in predicting critical hydrochar properties of higher heating value (HHV) and energy yield (EY). Through multiobjective optimization, we identify HTC conditions that simultaneously maximize HHV and EY for wood chips, corn straw, and sludge, with experimental validation confirming model robustness. We further demonstrate that optimally produced hydrochar can deliver net energy gains and reduce CO2 emissions by 396.6 million tons annually if deployed across China's agricultural residues and municipal sludge, equivalent to 3.3% of annual national emissions. This MoEs framework establishes a data-driven paradigm for scalable hydrochar design, enabling the targeted decarbonization of emission-intensive industries.

Microbial electrosynthesis (MES) enables CO2 conversion to multi-carbon fatty acids, but selective upgrading to longer-chain products remains limited by inefficient electron supply. This study developed a sequential MES platform using short-chain alcohols (ethanol, propanol, isopropanol) as exogenous electron donors to direct CO2 conversion into C4-C6 fatty acids. Ethanol preferentially promotes the formation of butyrate (C4, 0.42 g/L) and caproate (C6, 0.13 g/L), whereas propanol shifts selectivity towards valerate (C5, 0.51 g/L), while isopropanol exhibits lower chain-elongation efficiency. These trends demonstrate that the carbon skeleton of the electron donor governs elongation pathways and product distribution. Predicted functional profiling and microbial community analyses indicate a higher genetic potential for key chain-elongation pathways in ethanol-fed systems, consistent with improved electron transfer and altered metabolic flux distribution. Collectively, this study establishes short-chain alcohol supplementation as an effective strategy to modulate carbon flux and selectively synthesize multi-carbon fatty acids from CO2.

Efficient CO2 delivery remains a key bottleneck in electrocatalytic CO2 reduction due to the low solubility and sluggish diffusion of CO2 in aqueous electrolytes. Here we demonstrate that rational modulation of the interfacial microenvironment can effectively alleviate these mass-transport constraints and substantially enhance reaction efficiency. Hydrophobic channels constructed by embedding polytetrafluoroethylene nanoparticles enrich the local CO2 concentration and facilitate rapid gas-liquid transport, as supported by finite-element simulations. This microenvironmental engineering enables CO Faradaic efficiency of 94.6% at-0.8 V versus the reversible hydrogen electrode. Further incorporation of a conductive and hydrophobic polythiophene layer balances gas accessibility with charge-transfer kinetics, delivering CO Faradaic efficiency exceeding 98.6% and sustaining above 90% during the continuous operation in a flow-cell configuration. This work highlights the pivotal role of interfacial microenvironment regulation in overcoming intrinsic transport limitations, offering a robust strategy for highly efficient and durable CO2-to-CO conversion.

While photo‐ and electrochemical CO 2 reduction efficiently generate C 1 –C 2 molecules (e.g., formate, carbon monoxide, methane, ethylene), their limited selectivity and kinetic constraints impede direct C 2+ synthesis. Conversely, biological CO 2 fixation excels at producing multicarbon compounds (e.g., glucose, fatty acids, biopolymers) but requires energy‐intensive substrates. This Review explores the transformative potential of hybrid abiotic–biotic systems, where tailored C 1 –C 2 electron mediators synergize inorganic catalysis with biological conversion to enable scalable C 2+ production. We critically evaluate: i) recent breakthroughs in photo/electrocatalyst design, reactor engineering, and mechanistic control of C 1 –C 2 production; ii) engineered microbial and enzymatic pathways (autotrophic, mixotrophic, and synthetic) that optimize carbon flux toward C 2+ targets; and iii) integrated system architectures (in situ and spatially segregated), emphasizing mediator biocompatibility, mass‐transfer kinetics, and reactor scalability. A focused analysis highlights paired anodic processes (e.g., biomass oxidation) as energy‐efficient alternatives to the oxygen evolution reaction. Techno‐economic and life‐cycle assessments identify key bottlenecks, including mediator toxicity, system integration, and anodic byproduct valorization. By synthesizing interdisciplinary progress, this work identifies pathways to advance C 2+ production and establishes a roadmap for next‐generation CO 2 upgrading technologies.

Advanced biofuels in the form of liquid hydrocarbons offer a pathway to decarbonize long-distance heavy transport. Integrating biological acidification with electrocatalytic Kolbe-type decarboxylation provides a promising route for selectively producing linear hydrocarbons from biowaste. However, such cascading systems face challenges including suboptimal carbon utilization, limited product selectivity, and energy-intensive separations. This paper explores microbial chain elongation for generating medium-chain carboxylic acids (MCCAs) from biowaste, alongside CO2 reduction to supply biocompatible electron donors and improve carbon efficiency. Particular attention is placed on waveform-controlled electrosynthesis, which enables selective upgrading of MCCAs into alkanes and alkenes under mild conditions. Framed within a circular bioeconomy, key mechanistic, engineering, and techno-economic gaps are identified to advance bio-electrified hydrocarbons as competitive drop-in fuels.

Conversion of CO2 and H2 into biomethane is a promising technology within the concept of power-to-X. However, the integration of high-value-added products can enhance the economic viability and diversify future biobased production chains. Herein, an integrated biosystem converting CO2/H-2 into acetic acid, which is further converted to C4+ fatty acids, was demonstrated with the aim to assess the role of carbonaceous materials (model nanomaterial graphene and cost-effective biochar) and external electron donor (ethanol). With the supplementation of ethanol as the electron donor, carbonaceous materials significantly increased the production and selectivity of butyrate (C4) and caproate (C6) due to enhanced microbial growth and chain elongation efficiency. The highest concentration of butyrate (2512.35 +/- 60.05 mg/L) was observed in the graphene-added group, while the highest concentration of caproate (396.74 +/- 14.83 mg/L) was observed in the biochar group, suggesting different mechanisms induced by carbonaceous materials. Microbial community analysis revealed that carbonaceous materials primarily enriched members of the genus Clostridium_sensu_stricto_12, which are identified as typical carbon chain elongating microorganisms. Functional prediction revealed that carbonaceous materials increased the relative abundance of functional genes encoding crucial enzymes involved in both the Wood-Ljungdahl pathway and the fatty acid biosynthesis pathway. This study demonstrated an integrated approach for the efficient conversion of CO(2 )to value-added green chemicals.

The conversion of biomass residues into biochar is a promising strategy for enhancing sustainability within the circular bioeconomy, particularly through its role in improving renewable natural gas production. However, engineering biochar with optimal properties remains a complex challenge, as the relationship between preparation conditions, biochar characteristics, and anaerobic digestion (AD) performance is not fully understood. This study presents an AI-derived full-process prediction approach that integrates machine learning and generative models to guide the rational design of biochar, and optimize its use for biomethane production. Three tree-based regression models were employed to predict AD performance, with the eXtreme Gradient Boosting Regression model demonstrating superior accuracy. Feature importance analysis identified key biochar properties, including electrical conductivity, oxygen content, and specific surface area, as critical factors influencing biomethane production. These properties can be fine-tuned by adjusting pyrolysis conditions and selecting suitable biomass sources. A generative adversarial network was further used to explore a broader data space, helping to identify the optimal combination of parameters for maximizing AD efficiency. This novel AI-driven framework facilitates biochar-mediated renewable natural gas production, offering a scalable and sustainable approach for advancing circular bioeconomy.

Integrating microbial electrolysis cells and anaerobic digestion (MEC-AD) improves upon conventional anaerobic digestion for biomethane production due to the in-situ provision of electrochemically produced reducing power (such as hydrogen). However, the electron transfer behaviour at the microbe-electrode interface remains unclear. This study assessed the micro-scale interface modification of a carbonaceous bioelectrode, leading to an enhanced local electric field, which was postulated to stimulate electro-methanogenesis. The effectiveness of incorporating electro-conductive biochar to enhance interspecies electron transfer was also evaluated for its potential to boost biomethane production. The findings revealed a notable increase in biomethane yield and methane content within the biogas of the MEC-AD system, with improvements of 96.8 % and 32.5 %, respectively, compared to conventional anaerobic digestion when co-digesting grass silage and cattle slurry. The enhancement was ascribed to the accumulation of charges and an intensified local electric field on the surface of the etched biocathode, thereby facilitating interfacial electron transfer. Incorporating 10 g/L of biochar to conventional anaerobic digestion resulted in a 7.9 % increase in biomethane yield compared to conventional anaerobic digestion. Overall, the heightened energy yield of biomethane by the MEC-AD system (featuring the modified graphite cathode) resulted in a 6.5-fold increase compared to the additional electrical energy input. This underscores the catalytic significance of the electricity in AD system.

Closed-loop systems enable circular economy systems and applications in the food and beverage sector to enhance decarbonisation. Whiskey distillation by-products are amenable to anaerobic digestion and thus facilitate resource recovery and circularity. Furthermore, biochar derived from whiskey barrels can be used as a carbonaceous additive within anaerobic digestion to enhance biomethane production. In this paper, biochar produced from the pyrolysis of discarded whiskey barrels at 300 degrees C, was shown to enhance biomethane production by up to 15 %. A kinetic analysis revealed that the biochar reduced the biomethane lag time by up to 42 %. The mass and energy balance of this integrated anaerobic digestion-pyrolysis system was evaluated. The overall system efficiency was assessed at 68 % of all input energy (expressed on a primary energy basis); utilisation of renewable electricity could increase this efficiency to 71 %. Biochar from discarded whiskey barrels can provide a decarbonisation pathway for whiskey distilleries but may be constrained by the total resource available.

Food waste represents a valuable resource potential for the production of advanced biofuels, including biomethane. This study systematically assessed the impact of salt on biomethane production from different components of food waste. The highest biomethane yields of 258.89 +/- 10.96, 337.52 +/- 16.36, and 448.49 +/- 23.375 mL/g volatile solids (equivalent to biodegradability indexes of 75.75%, 88.92% and 92.66%) were achieved from cellulose-rich, starch-rich and protein-rich components, respectively, at a salt concentration of 3 g NaCl/L. The biomethane yield was improved by 9.69-31.24% with low-concentration salt compared with no salt addition, but it was inhibited by high salinity. Inhibition induced by high salinity (15 g NaCl/L) on biomethane production followed the order of protein (15.50%) < starch (28.03%) < cellulose (42.92%). Co-digestion of different components effectively mitigated the inhibitory effect of salt on biomethane production. Microbial community analysis revealed that archaea were significantly affected by high salinity. With a high concentration of salt (15 g/L), acetoclastic methanogens (Methanosatea) predominated in the digestion of starch-rich components, whilst hydrogenotrophic methanogens (Methaonmassiliicoccus and Methanobacterium) predominated in the digestion of cellulose-rich and protein-rich components. Additionally, some salt-tolerant microorganisms (SC103, Thermovirga and Methanosarcina) were selectively enriched at high salinity.

Biohythane (a mixture of hydrogen and methane) may play a significant role in a future decarbonised energy system. The production of biohythane can be achieved by sequential dark hydrogen fermentation and anaerobic digestion. However, the technology readiness level of biohythane can be limited by many process constraints negatively affecting its commercial feasibility. Here, a pilot experiment on fermentative hythane production from cassava stillage residue (CSR) incorporating dilute acid pretreatment and enzymolysis was undertaken. The production of hydrogen and methane was 72.0 +/- 10.7 and 295.4 +/- 28.5 mL/ g volatile solid, respectively. Different scenarios for techno-economic analysis were developed in terms of the dried/wet form of CSR and total solids content during fermentation. Results suggested that hythane from CSR was not economically feasible with a high production cost (1.39-2.33 euro/m3). There was a trade-off relationship between the increase in methane yield through pretreatment and the associated cost. (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Microbial electrosynthesis is advantageous in producing valueadded C1+ molecules from CO2, complementing electrocatalysis that is efficient in producing C-1 molecules such as carbon monoxide and formate. However, a full understanding of microbe-electrode interactions at the biocathode is lacking, leading to suboptimal electron transfer efficiency. The interfacial electron transfer and biofilm formation on a constructed 3D cobalt-nickel-bimetallic-sulfide- coated carbon felt (CoNi-CF) biocathode were explored. Honeycomb-like metallic nanocrystals on CoNi-CF provide ample active sites for efficient electron transfer to microbes. Nanometer-sized tips on biocathodes intensify local electric fields, enabling efficient charge transfer and HCO3-/CO2 bio-electroreduction. Density functional theory analysis shows the catalysts effectively bind hydrogen atoms, crucial for facilitating interfacial charge transfer in biological metabolisms. The overall faradic efficiency of acetate and ethanol reaches 90.8% due to the constructed biocathode. This study advances understanding of abiotic-biotic electron transfer mechanisms, offering potential for efficient microbial electrosynthesis of chemicals from CO2.

Lignin extraction from lignocellulosic biomass can enhance its bioconversion efficiency, whilst the recovered lignin can provide added economic value. This study comprehensively investigated the impacts of short-chain carboxylic acid-based deep eutectic solvents (DESs) pretreatments on lignin extraction from willow and assessed subsequent biomethane production through anaerobic digestion. Process parameters (including the DESs type, molar ratios of DESs components, temperature and reaction time) in the DESs pretreatments of willow for lignin extraction were optimized using the central composite surface response methodology. Results showed that lactic acid-based DES pretreatment outperformed acetic acid and propionic acid-based DES pretreatments in terms of lignin removal efficiency and methane production. Under the optimal conditions (choline chloride:lactic acid with a molar ratio of 1:10 at 160 degrees C for 15 min) lactic acid-based DES pretreatment retained over 94% of the glucan content in the raw willow whilst achieved the highest lignin removal of 80%. The recovered lignin showed a purity of above 81%. Compared with the biomethane production of 89.9 mL/g total solid from raw willow, the biomethane production significantly increased by 36.3% after the lactic acid-based DES pretreat-ment. The optimal condition reduced the digestion time from 22 to 10 days. The overall energy conversion efficiency of 62.7% demonstrated that lactic acid-based DES pretreatment of lignocellulose could be a promising method to co-produce renewable gaseous fuels and lignin in a sustainable approach.

Production of renewable C1 transport biofuels (such as biomethane and biomethanol) through the integration of anaerobic digestion (AD) with carbon capture, utilization and sequestration technologies may offer a solution to reduce greenhouse gas (GHG) emissions. This paper presented a detailed techno-economic and environmental assessment of four cases for biomethane or biomethanol production by incorporating AD, CO2 utilization via biomethanation (CU), solid digestate pyrolysis (Py) and methanol synthesis (MeOH). The results reflected the current state of technologies and potential future scenarios within a mature market. Under optimistic scenarios (scaled-up systems and reduced hydrogen price of 1 euro/kg), the minimum potential GHG abatement cost for the AD-Py-CU case was-111.1 euro/t CO2-eq when biomethane was sold at 1.03 euro/Nm3 (a contract gas price in 2022), while the abatement cost rose to-58.2 euro/t CO2-eq when H2 was purchased at 3.40 euro/kg. When methanol was sold at 425 euro/t (global weighted average value), the marginal abatement cost for the AD-Py-CU-MeOH (with H2 at 1.0 euro/kg) case was 136.5 euro/t CO2-eq, which is higher than current carbon credits at 33.5 euro/t CO2. This study suggests that biomethane produced by incorporating AD, CO2 biomethanation and pyrolysis technologies may be economically and environmentally competitive over natural gas.

Lignocellulosic biomass can add to the worldwide resource of biogas; however, the aromatic structure of lignin is recalcitrant which impairs biodegradation. Direct interspecies electron transfer (DIET) may overcome limitations in the biodegradation of lignin derivatives. Within a circular bioeconomy system, lignin-derived biochar and activated carbon were assessed for their ability to enhance the digestion of a typical lignin monomer - syringaldehyde. Biochar at 5-10 g/L significantly reduced the lag-phase time by 33-42% possibly due to the enhancement of syntrophic hydrogenotrophic methanogenesis. In comparison, activated carbon at 1-10 g/L reduced the lag-phase time by 46-85% and significantly accelerated the degradation of volatile fatty acids, due to a combinational effect of enhanced syntrophic oxidation and DIET. When activated carbon was added at a higher dosage of 20 g/L, the highest biomethane yield (426.6 ml/g) was achieved; an increase of 33% compared to the digestion of syringaldehyde alone. The enhancement was ascribed to the metabolic shift from the hydrogenotrophic to the DIET pathway, which could be implied from the microbial community dominated by Methanosaeta. The superior function of activated carbon over biochar was speculated to be associated with its larger surface area and higher abundance of the C--O group.

Lower crust-derived granitic rocks provide constraints on the crustal reworking process and consequently give hints on the destruction mechanism of the cratons. The North China Craton (NCC) underwent extensive crustal melting in the Mesozoic. This study investigated granitic intrusions in the Dazeshan region of the Jiaodong Peninsula. Whole-rock major and trace element analyses and zircon U-Pb ages coupled with Hf isotopes were used to reveal the crustal reworking processes. Zircons separated from the quartz porphyry, Linglong granite, rhyolite porphyry, and biotite granite showed weighted mean 206 Pb- 238 U ages of 119.2 ± 1.0 Ma, 140.2 ± 1.0 Ma, 120.6 ± 0.5 Ma, and 119.9 ± 0.7 Ma, respectively. The quartz porphyry, rhyolite porphyry, and biotite granite had high silica contents (SiO 2 = 74–77 wt.%) but low MgO, Co, and Ni concentrations. The calculated ε Hf (t) values for the rhyolite porphyry and the biotite granite ranged from −18.3 to −20.0 and −17.8 to −20.2, respectively. These geochemical features imply ancient crust sources. The quartz porphyry showed distinct primitive mantle-normalized rare earth element (REE) patterns and was characterized by lower ΣREE content and lack of pronounced negative Eu anomalies. Whole-rock and zircon Dy/Yb ratios showed no correlation with whole-rock Rb/Sr ratios and zircon Hf contents, reflecting limited effects of crystal fractionation. The Ba/La ratios were also high (>150), but the Sr/Y and La/Yb ratios were low (Sr/Y < 50; La/Yb < 15). These features likely indicate that the quartz porphyry was generated by water-fluxed melting without differentiation. The rhyolite porphyry and biotite granite shared many geochemical similarities, denoting a unified source. The high La/Yb (>30) but low Sr/Y (<20) ratios and apparent negative Eu anomalies indicated plagioclase fractionation. Decreased zircon Dy/Yb with increasing Hf concentrations reflected noticeable amphibole fractionation. These two suites had fairly low Ba/La ratios. These data together point toward an identical source: dehydration melting of a relatively thickened crust. These melts experienced crystal fractionation after extraction. We propose that the intrusions were generated by the underplating of water-rich mafic magma, which provided both fluid and heat and finally induced two kinds of melting.

On-farm feedstocks such as grass silage and cattle slurry present recalcitrant characteristics that can limit microbial conversion in biofuel production. Introducing a biochar supplement in two-stage anaerobic digestion may facilitate feedstock hydrolysis and improve energy yields in biohydrogen and biomethane production. The biomethane potentials were first investigated in batch trials without biochar supplement; results indicated a biomethane yield of 230 L per kilogram (kg) volatile solid (VS) in single-stage digestion and 275 L/kg VS in twostage digestion. In continuous trials, operated at an organic loading rate of 4.0 g VS/L/d, the second-stage digester in two-stage digestion showed a methane yield of 237 L/kg VS with 10 g/L biochar addition; this was 7% higher than the second-stage digester without biochar addition. At the same loading rate of 4.0 g VS/L/d, the biomethane yield in continuous single-stage digestion with 10 g/L biochar addition was 212 L/kg VS; this was 3% higher than the single-stage digester without biochar addition. Biochar was found to enhance the hydrolysis of recalcitrant solid components in the hydrogen-producing phase, promote biomethane production in methanogenesis, and stabilize the digestion process. The highest energy yield of 8.5 MJ hydrogen and methane per kg VS was achieved in the two-stage digestion with 10 g/L biochar addition at a loading rate of 4.0 g VS/L/d. The results demonstrated that the application of a biochar supplement could effectively enhance gaseous biofuel production in two-stage anaerobic digestion.

Grass silage and cattle slurry are the most abundant feedstocks for biogas in an Irish context. This work describes how to optimize their biomethane yield. Hydrolysis and biomethane yields from co-digestion of grass silage and slurry were enhanced in a biochar-supplemented two-stage digestion process. Biochar addition at the optimal dosage of 10 g/L in batch two-stage digesters led to the highest methane yield of 253 L per kilogram (kg) volatile solid (VS), which was 24% higher than that from two-stage digesters without biochar supplementation. For a batch single-stage digester, the biomethane yields were lower than the two-stage but 10 g/L biochar addition led to an increase to 218 L/kg VS as compared to 198 L/kg VS for the group without biochar supplementation. Volatile fatty acid accumulation increased with the enhancement of biomethane production in the biocharsupplemented two-stage reactors. The addition of biochar in single-stage and two-stage anaerobic digesters presented positive effects on the electrochemical properties of the digester contents, reflected by the increased charge storage capacity, reduced solution resistance and improved digester content conductivity. The methane yields in two-stage anaerobic digestion were shown to be strongly correlated (R2 = 0.92) with the concentration of extracellular polymeric substances. This evidenced that the interlaced conductive network established by extracellular polymeric substances and biochar was essential for direct interspecies electron transfer and biomethane production. This study demonstrated that biochar-supplemented two-stage anaerobic digestion is an optimal route for energy recovery from grass silage and cattle slurry.

Using renewable biogas from the anaerobic digestion of distillery by-products as a low-carbon heat source can decarbonize the distillery process and support the distillery industry to transition to a more sustainable production process. This study investigated the anaerobic digestion performance of different types of whiskey byproducts and the effects of acid pretreatment on the digestion of solid by-products. Results of biomethane potential assays showed that the methane yield from the unprocessed by-products was 330 mL/g volatile solids (VS) from draff, 495 mL/g VS from thin stillage, and 503 mL/g VS from thick stillage. For the processed by-products the specific methane yield was 370 mL/g VS from cake maize, 382 mL/g VS from wet distillers' grains with solubles (WDGS), and 545 mL/g VS from syrup. Acid pretreatment (1% H2SO4 at 135 C for 15 min) did not significantly improve the methane yield from solid by-products (such as draff and WDGS) but reduced the digestion time by 54.5% for cake maize. The microbial community analysis revealed that methane production from the untreated and acid-pretreated solid by-products (draff and WDGS) was mainly through the hydrogenotrophic methanogenesis pathway. The gross thermal energy in the form of methane produced from 100 tonnes of mixed unprocessed by-products (draff, thin stillage, and thick stillage) was calculated as 24.4 MW(th)h equivalent to 60.6% of the thermal energy consumed in whiskey production, which effected the same percentage of CO2 emissions reduction.

Microbial chain elongation fermentation is an alternative technology for medium-chain fatty acid (MCFA) production. This paper proposed the addition of pyrochar and graphene in chain elongation to improve MCFA production using ethanol and acetate as substrates. Results showed that the yield of, and selectivity towards, C6 n-caproate were significantly enhanced with pyrochar addition. At the optimal mass ratio of pyrochar to substrate of 2 g/g, the maximum n-caproate yield of 13.67 g chemical oxygen demand/L and the corresponding selectivity of 56.8% were obtained; this represents an increase of 115% and 128% respectively as compared with no pyrochar addition. Such improvements were postulated as due to the high electrical conductivity and surface redox groups of pyrochar. The optimal ethanol to acetate molar ratio of 2 mol/mol achieved the highest MCFA yield under pyrochar mediated chain elongation conditions. Thermodynamic calculations modelled an energy benefit of 93.50 kJ/mol reaction for pyrochar mediated n-caproate production.