Search Results (334)

In silico structural characterization of carbohydrate-active enzymes (CAZymes) in Bacillus subtilis T7 reveals mechanistic insight into the strain’s capacity for consolidated bioprocessing of untreated lignocellulosic biomass. Homology models for 13 CAZymes were constructed using SWISS-MODEL, with Cu²⁺ and FAD cofactors incorporated into the AA10 lytic polysaccharide monooxygenase and AA3 oxidoreductase models, respectively. Blind molecular docking across the full protein surface identified energetically favorable binding pockets on GH9 endoglucanase and Abhydrolase_1. Among 12 enzyme–ligand pairs screened, Abhydrolase_1 exhibited the highest affinity for xylotetraose (−7.7 kcal/mol) and GH9 showed the strongest preference for cellotetraose (−7.0 kcal/mol). Site-specific docking confirmed six hydrogen bonds with Gly32, Phe33, Thr34, Ser36, Arg179, and His256, supplemented by two carbon–hydrogen bonds with Ile180 and Ser39, anchoring xylotetraose within the Abhydrolase_1 binding cavity, and seven hydrogen bonds stabilizing cellotetraose in the GH9 catalytic groove, with key contacts at Tyr141, Trp145, Asp194, Trp193, Arg254, Tyr255, and Tyr354. One-hundred nanosecond all-atom molecular dynamics simulations (GROMACS 2023.2, CHARMM36 force field, triplicate runs) confirmed overall structural integrity for both proteins: Abhydrolase_1 maintained a compact conformation (Rg = 18.11 ± 0.09 Å; backbone RMSD 2–3 Å), while GH9 was similarly stable (Rg = 30.36 ± 0.33 Å; RMSD 2–5 Å). Ligand dynamics were more variable—xylotetraose remained bound within the Abhydrolase_1 active site for approximately 75 ns before partial displacement, whereas cellotetraose exhibited dynamic association along the GH9 catalytic channel, consistent with processive substrate translocation in endoglucanases. These computational findings line up with the strain’s experimentally observed hydrolytic clearance zones (cellulase 24.5 mm; xylanase 11.6 mm), 63.4% alkali lignin decolorization, transient accumulation of ferulic acid and vanillin, and a hydrogen yield of 1.41 mol H₂/mol substrate from untreated food waste. Together they give a molecular-level picture of substrate-specific CAZyme recognition in B. subtilis T7 and support its potential as a pretreatment-free platform for lignocellulosic biohydrogen production. Full article

Biological hydrogen production from lignocellulosic residues is increasingly recognized as a promising route toward sustainable fuel production. However, efficient conversion of these materials requires appropriate pretreatment strategies to enhance carbohydrate accessibility while preserving the quality of the resulting hydrolysates for fermentation to hydrogen. To date, most pretreatment studies have primarily emphasized maximizing sugar release and biomass fractionation, often overlooking the critical role of hydrolysate quality and hydrogen fermentability. This review evaluates lignocellulosic biomass pretreatment technologies with a specific focus on their impacts on hydrogen fermentability. Among all of the well-studied pretreatments, only a few are good candidates for biohydrogen production from lignocellulosic biomass. In particular, the selection of an optimal pretreatment approach was shown to depend not only on the physicochemical characteristics of the biomass but also upon the metabolic capabilities and substrate utilization patterns of the microorganisms employed. This article highlights the need for integrated optimization of pretreatment and fermentation processes and identifies key challenges and opportunities for advancing lignocellulosic biohydrogen production. Full article

Dynamic membrane bioreactors (DMBRs) are promising systems for continuous biohydrogen production because they enable effective biomass retention under short hydraulic retention time (HRT) conditions. In this study, a dynamic membrane bioreactor coupled with electro-fermentation (DMBR-EF) was operated for 59 days to investigate the effect of applied voltage on biohydrogen production and metabolic flux regulation. The reactor was sequentially operated at 0 (no applied voltage), 0.2, 0.4, 0.6, 0.8, and 1.0 V using glucose as a model substrate. The highest hydrogen production rate (HPR) and hydrogen yield (HY) were achieved at 0.2 V, reaching 15.35 ± 0.48 L H₂/L/d and 1.54 ± 0.05 mol H₂/mol glucose_added, respectively, which were 33.71% and 33.91% higher than those of the 0 V control. At 0.2 V, residual glucose and effluent volatile suspended solids (VSS) were minimized, while butyric acid (HBu) formation was enhanced and lactic acid (HLa) accumulation was suppressed. In contrast, voltages above 0.4 V reduced hydrogen recovery by shifting metabolic flux toward HLa, propionic acid (HPr), formic acid (HFo), and homoacetogenic pathways. Microbial analysis showed that Clostridium dominated under all conditions, but voltage application selectively altered the relative abundance and metabolic output of Clostridium-related amplicon sequence variants (ASVs). These results indicate that mild electrochemical stimulation at 0.2 V effectively enhances continuous biohydrogen production by promoting butyric acid-type fermentation, suppressing lactic acid accumulation, and reducing hydrogen loss through competing metabolic pathways in DMBR-EF systems. Full article

Dark fermentative biohydrogen (bio-H₂) production is a promising renewable energy technology for converting organic waste and wastewater into clean fuel. However, practical application is limited by low H₂ yield, volatile fatty acid (VFA) accumulation, incomplete substrate utilization, electron diversion to competing pathways, prolonged lag phases, and inhibitory byproducts from lignocellulosic pretreatment. Magnetite nanoparticles (Fe₃O₄ NPs) have attracted attention as redox-active additives because of their electrical conductivity, reversible Fe²⁺/Fe³⁺ cycling, magnetic recoverability, biocompatibility, and microbial interaction potential. This review examines the physicochemical properties of Fe₃O₄ NPs and their proposed roles in dark fermentative bio-H₂ production. Particular emphasis is placed on Fe₃O₄-mediated extracellular electron transfer (EET) in fermentative communities, which differs from direct interspecies electron transfer (DIET) in methanogenic systems. Fe₃O₄ NPs may enhance bio-H₂ production by facilitating electron transfer, supporting hydrogenase activity, regulating redox balance, promoting acetate- and butyrate-type pathways, and enriching H₂-producing bacteria such as Clostridium spp. Hybrid systems combining Fe₃O₄ with biochar, activated carbon, reduced graphene oxide, bimetallic nanocomposites, or immobilization matrices may further improve microbial retention and process stability. Remaining challenges include aggregation, dosage-dependent toxicity, recovery, environmental fate, mechanistic uncertainty, and scale-up feasibility. Full article

In this study, an ecofriendly microfluidic microbial biocathode electrolysis cell is developed for hydrogen production. Low-cost microbial catalysts are employed on single-walled carbon nanotube cathodes instead of noble metal (platinum) catalysts. The channel layer for the electrolyte flow is fabricated from polydimethylsiloxane and coated with Parylene C to minimize oxygen permeability. A miniaturized electrolysis cell is constructed by depositing electrodes onto a glass substrate and bonding them to a polydimethylsiloxane channel layer via plasma surface treatment. The establishment of the biocathode during the start-up procedure is analyzed, and the hydrogen production performance of the biocathode microbial electrolysis cell (MEC) is evaluated under various applied voltages and electrolyte flow rates. At higher applied voltages and optimal flow rates, biofilm formation is well-developed, resulting in a peak hydrogen production rate of 14.8 m³ H₂ m⁻³ d⁻¹. The developed MEC biocathode demonstrates significant performance, achieving a current density of 0.22 A m⁻², corresponding to 69% of that of a platinum-catalyzed cathode MEC, while exhibiting a substantially longer operating duration of 12 h. These results demonstrate the potential to overcome the inherent limitations of biocathodes, thereby addressing the high cost and low durability of conventional platinum-catalyzed MECs. Compared with conventional MEC systems, the proposed microfluidic configuration enables membraneless operation with reduced internal resistance and rapid biofilm formation, demonstrating its potential as a compact and cost-effective platform for biohydrogen production. Full article

Hydrogen is increasingly recognized as a key energy carrier for decarbonizing hard-to-electrify sectors, yet more than 95% of current global production remains fossil-derived. Biological hydrogen (biohydrogen) produced by dark fermentation (DF), photo-fermentation (PF), or microbial electrolysis cells (MEC) offers the dual advantage of valorizing organic wastes while delivering low-carbon H₂; however, none of these standalone technologies mobilizes more than 25–33% (DF), 40–70% (PF), or 40–60% (MEC) of feedstock organic carbon through H₂-producing oxidation pathways. Most existing reviews compare these pathways on hydrogen yield alone, a metric that conceals where the majority of feedstock carbon and electrons are actually lost and obscures the quantitative rationale for system integration. This review reframes the comparison around carbon and electron flow, explicitly tracking how much input carbon is mobilized through H₂-producing oxidation pathways, how much is retained in volatile fatty acids (VFAs), biomass, or unlinked CO₂, and what happens to the associated electrons. Stoichiometric, mechanistic, and reactor-level evidence is synthesized to show that DF channels only 25–33% of input organic carbon through H₂-yielding decarboxylation on real heterogeneous substrates, with 40–60% retained as residual VFAs and unhydrolyzed solids; PF can recover 60–80% of VFA carbon but is constrained by photon economics and nitrogenase sensitivity; and MEC achieves >85% COD removal only when coupled to an upstream acidogenic stage. Two-stage (DF–PF, DF–MEC) and three-stage (DF–PF–MEC, DF–MEC–AD) configurations are critically evaluated, with theoretical yields separated from experimentally demonstrated performance on real wastes and hidden energy inputs (pretreatment, inter-stage transfer, gas separation, and compression) explicitly accounted for. DF–MEC coupling is identified as the most near-term tractable configuration, achieving 55–70% H₂-pathway carbon mobilization and 80–92% COD removal at an electrical input of 0.9–1.5 kWh/m³ H₂, with levelized hydrogen costs of US$3–5.5/kg under favorable waste-tipping-fee conditions. Multi-stage systems push carbon recovery above 70% but carry unresolved capital, methanogenesis control, and scale-up penalties. This review closes by proposing a standardized ten-descriptor reporting framework including H₂-pathway carbon mobilization (%), cathodic hydrogen recovery (rCAT), net energy recovery (NEB), and LCA carbon intensity under both attributional and consequential boundaries, and demonstrates its backward compatibility by retrospective application to seven studies already in the literature. Research priorities tractable on a 5–10 year horizon are identified, centered on methanogen suppression at pilot scale, real-waste MEC performance, and renewable-electricity coupling. Full article

The transition to renewable energy requires scalable and sustainable hydrogen production technologies. Dark fermentation (DF) can generate biohydrogen from diverse biomass feedstock, but its efficiency remains limited. Immobilising anaerobic consortia offers a route to improve performance. This study reports on the immobilisation of whole cells in hybrid biochar–alginate beads (BAB) compared with control alginate beads (CAB) during DF. Biochar from oakwood and water hyacinth, pyrolysed at 450 and 600/650 °C, were incorporated into BAB. BAB increased biohydrogen production rates by 1.4–2.6-fold relative to CAB, driven by enhanced microbial attachment, synergistic interactions, and improved mass transfer. High-temperature biochar generated the strongest effects, raising hydrogen yield by up to 23% and shortening the lag phase by 94%. Biochar properties, including porosity, surface area, inorganic content, electrical conductivity and buffering capacity, likely support these effects. These results establish hybrid biochar-alginate support as a promising platform to accelerate DF and advance biohydrogen as a sustainable biofuel. Full article

Global demand for sustainability drives interest in bioenergy from sustainable feedstock. Agro-industrial waste such as brewer’s spent grains (BSG) is an important by-product of brewing. This study provides a comprehensive review of the current technologies of BSG for energy recovery and BSG-based materials for energy storage applications. The latest scientific progress, not only from conventional processes on anaerobic digestion, combustion, gasification, pyrolysis, torrefaction, and hydrothermal liquefaction but also from several integrated technologies, pretreatment methods, and additives/catalysts regarding the improvement of energy efficiency and process sustainability, was reviewed. In addition, the co-feedstock practices (co-combustion, anaerobic co-digestion, hydrothermal co-liquefaction, anaerobic co-fermentation) and co-production were examined. AD of BSG yields about 302 NL CH₄/kg COD, generating roughly 0.39 kWh of electricity/kg BSG and 1.71 MJ of thermal energy/kg BSG. Ultrasonic pretreatment enhances methane production up to four times (107 L CH₄/kg TVS) and reduces CO₂ emissions by 0.083 t CO₂eq/t BSG. Anaerobic co-digestion of BSG with other brewery waste increased the yield up to 88 mL CH₄/g TVS, generated approx. 0.348 kWh/kg TVS electricity, and reduced emissions by 0.114 kg CO₂eq/kg TVS. Bioethanol yields can reach 72%, while biohydrogen generation was up to 5154 mL H₂/g glucose. BSG pyrolysis provides up to 71.8% bio-oil, and its calorific value is 18–25 MJ/kg. BSG-derived activated biocarbon has a notable surface area (1792 m²/g) for lithium–sulfur batteries. The assessment showed that BSG’s transformation into bioenergy and energy storage materials aligns with waste reduction and sustainable development goals. However, future research on combined alternative wastes, integrated technologies, green nanotechnology, and artificial intelligence technology could lead to optimal performance and facilitate their industrial application. Full article

The growing demand for sustainable energy carriers has intensified interest in hydrogen production from renewable resources and waste-derived substrates. In this context, microbial electrolysis cells (MECs) have emerged as a promising technology for the simultaneous treatment of organic waste and biohydrogen generation. This review provides an overview of recent advances in MEC systems, focusing on reactor configurations, performance indicators such as hydrogen production rate, coulombic efficiency, and chemical oxygen demand removal. Attention is given to the valorization of real waste streams, including municipal and agro-industrial effluents, highlighting the differences between laboratory- and pilot-scale applications. While numerous studies have demonstrated the technical feasibility of MECs, several bottlenecks still limit their large-scale implementation, including challenges associated with the use of complex substrates. In particular, untreated wastewater often leads to reduced process efficiency due to its variable composition and the occurrence of competing microbial pathways. To overcome these limitations, integrated approaches are also discussed, with emphasis on the coupling of dark fermentation, capable of enhancing substrate biodegradability through the production of volatile fatty acids, with MEC systems. Overall, MEC technology represents a promising pathway for sustainable hydrogen production within circular waste management frameworks, although further advancements are required to enable its practical application. Full article

Municipal Solid Waste (MSW) gasification presents a promising pathway for low-carbon bio-hydrogen production. However, MSW is underrepresented as a feedstock in the gasification literature due to its heterogeneity, and fewer studies have leveraged Box–Behnken experimental design in gasification simulation studies or investigated the interaction between equivalence ratio and steam–feed ratio. This paper develops a thermodynamic equilibrium model in Aspen Plus^® (V14) to simulate oxy-steam gasification of MSW derived from the Phyllis database, with subsequent optimisation using Box–Behnken Design. Sensitivity results confirm literature trends, with hydrogen yield generally increasing with gasification temperature and steam–feed ratio up to an optimum threshold, while an increasing equivalence ratio suppresses hydrogen formation. An optimum hydrogen volume fraction of 51.77% in the syngas composition was achieved at a gasification temperature of 873 °C, equivalence ratio of 0.3, and a steam-to-feedstock ratio of 0.5. The study revealed a comparatively smooth response surface between equivalence ratio and steam–feed ratio, and a statistically insignificant effect of equivalence ratio on hydrogen formation in steam gasification. This provides new insight into gasification systems, whereby, within the investigated equivalence ratio (ER) ranges of 0.2–0.4, steam can effectively drive hydrogen-enhancing reactions, thereby reducing the relative importance of oxygen supply in oxy-steam gasification. The study could provide useful guidance on experimental design for hydrogen production through steam gasification. Full article

Acidogenic fermentation of organic wastes represents a strategic platform for the co-production of H₂, CO₂, and volatile fatty acids (VFAs), which are potential key intermediates for cost-effective polyhydroxyalkanoate (PHAs) biosynthesis. This typically relies on carbon sources that are too expensive and hinder the commercialization of PHAs. This study provides metagenomic insights into the microbial dynamics underpinning the acidogenic conversion of waste melon under increasing organic loading rates (OLRs). Metabarcoding revealed that Megasphaera dominated the community, with its abundance rising markedly from 5 to 20 gCOD/L, accompanied by relevant contributions from Solobacterium, Prevotella, and Clostridium. These taxa were associated with the formation of acetic, propionic, and butyric acids and with enhanced hydrogenogenesis. Higher OLRs, up to 20 gCOD/L, promoted hydrogen-producing species while suppressing lactic acid bacteria, thereby improving H₂ and VFAs yields up to 26.7% v/v and 13 gCOD/L, respectively. By linking microbial shifts to metabolic outputs, this work advances the understanding of acidogenic pathways essential for integrating dark fermentation-derived H₂, CO₂, and VFAs into sustainable PHAs production systems. Full article

Cyanobacterial species in the Arabian Peninsula region display a diverse range of potential biotechnological application. This review summarizes the cyanobacteria diversity found in the Peninsula region, the bioactive compounds found in these species, and the several health benefits and applications. The Arabian Peninsula region comprises a wide range of cyanobacteria with representatives from the orders Oscillatoriales, Chroococcales, Stigonematales, and Nostocales. These microorganisms produce specialized metabolites such as photosynthetic pigments, pigment–protein complexes, lipopeptides, phenolic compounds, and unique secondary metabolites. Many of the metabolites offer beneficial biological functions including antioxidants, antibacterial, anti-cancer, anti-inflammatory antiviral, and neuroprotective ones. In addition to the medical-related practices, cyanobacteria in the Peninsula region might have several other applications. Other probable uses include their potential bioremediation capability to remove pollutants or heavy metals, as a potential biohydrogen source for renewable energy, and as biofertilizers and soil enhancement to support sustainable agriculture; other useful applications include bioplastics production (polyhydroxyalkanoates), soil microbiota improvement, and methane reduction. The review highlights the potential diverse biotechnological applications of Arabian Peninsula cyanobacteria toward bioremediation, bioplastics, ecosystem regeneration, biofertilizers, bioenergy, and agro-sustainability, as well as human health. This review highlights the importance of the further exploration and exploitation of these resourceful microorganisms for sustainable development in the Arabian Peninsula region. Full article

Dark fermentation is commonly used for producing biohydrogen as a green hydrogen, which can be used as an alternative to fossil fuels. Pilot-scale studies on continuous biohydrogen production from molasses are still limited. In this study, a 60 L pilot-scale up-flow anaerobic sludge bed (UASB) dark fermentation system was operated continuously for biohydrogen production from molasses. The reactor achieved an average hydrogen production rate of 3.64 L H₂/L-d. Attention was paid to evaluating total sugar, rather than COD alone, as a more appropriate process indicator for substrate conversion and hydrogen production performance. In addition, metabolic pathway characteristics and microbial community structure were examined. The results provide useful pilot-scale operational data for the implementation of fermentative biohydrogen production technology. Full article

The high-efficient utilization technology of organic waste can alleviate the dual pressures of energy and the environment. The study investigated the effects of substrate ratio, substrate concentration, and temperature on biohydrogen yield, and further optimized the process conditions for co-digestion of food waste and fecal sludge as substrates for biological hydrogen production. The results of batch mode experiments show that when the ratio of food waste to fecal sludge is 5:1, substrate concentration is 60 g/L, and fermentation temperature is 40 °C, the system achieves maximum cumulative hydrogen production of 183 mL (equivalent to 32 mL/g VS). The response surface methodology (RSM) indicates that substrate ratio, substrate concentration, and temperature all exert remarkably significant effects on hydrogen yield (p < 0.01). In addition, the synergistic interaction between substrate ratio and temperature significantly influences hydrogen production performance (p < 0.05). This study elucidates the synergistic mechanism of key process factors in the co-digestion of food waste and fecal sludge for biohydrogen production. The findings provide a theoretical basis for the engineering application of organic waste to hydrogen technologies. Full article

Ofloxacin (OFL) exists widely in raw materials of organic fermentation, which can inhibit hydrogen production of dark fermentation. In this study, the inhibition of OFL on hydrogen production was studied from the aspects of hydrogen production performance, bacterial community and functional genes using glucose as a model substrate. The results showed that OFL exposure ≥ 10 mg/L significantly decreased the hydrogen production. With an OFL exposure concentration of 500 mg/L, the hydrogen yield reduced to 48.35 ± 2.13 mL/g glucose and the lag period prolonged to 26.48 ± 0.40 h, compared with those of control without ofloxacin exposure (169.99 ± 9.68 mL/g glucose and 8.98 ± 0.07 h), respectively. The efficient hydrogen-producing bacteria, Clostridium, were inhibited and the dominant microbial population was transformed, leading to change in metabolic pathway of fermentation from butyric acid type to ethanol type. Correspondingly, the proportion of butyrate in metabolites decreased from 66.46% to 0.00%, the proportion of acetate decreased from 26.12% to 3.69%, and the proportion of ethanol increased from 3.13% to 96.31%. OFL exposure showed significant downregulation of predicted functional genes involved in glycolysis and hydrogen production, such as K00845, K00532, and K03737, fundamentally resulting in significant inhibition of glycolysis and pyruvate metabolism for hydrogen production. Full article