Search Results (372)

This study investigates the efficient biogenic production of hydrogen via the thermophilic bacterium Thermotoga neapolitana, focusing on optimising process configurations to maximise yield and productivity. To determine optimal conditions, a 1 L anaerobic bioreactor with online gas analytics was designed and tested for batch, fed-batch and continuous fermentation. A maximum hydrogen production rate of 96.1 ± 1.7 Nml·L⁻¹·h⁻¹ was observed in the continuous reactor. The optimal dilution rate was 0.07 h⁻¹. Each dilution rate was kept for ≥56 h fermentation time and resulted in yields of 2.7–3.0 mol_H2·mol_glucose⁻¹. A consistently high cell viability (97%) was also observed across various dilution rates. A detailed carbon balance indicates acetate as the main by-product, closely linked to the hydrogen production pathway. Compared to fed batch and batch, the hydrogen production rate could be increased and remain constant over a longer time. In this way the continuous reactor design showed an additional method to produce hydrogen to the established ones. Fermentative hydrogen production is particularly promising when using carbohydrate containing biomass and biowaste, as it can be considered carbon dioxide neutral. Full article

The aim of the study was to evaluate the feasibility of using exhaust gases as a CO₂ source in the cultivation of Tetraselmis subcordiformis microalgae for biomass and hydrogen production. It was shown that the growth rate of T. subcordiformis biomass and its biochemical composition depended on the CO₂ source. The highest growth rate of 286 ± 15 mgVS/L-d and a final biomass concentration of 2710 ± 180 mgVS/L were achieved in the variant where exhaust gases from a coal and biomass supplementary combustion plant were the CO₂ source (V2). The highest CO₂ reduction efficiency of 90.3 ± 3.2% was achieved in the case where waste gases from biogas combustion were the CO₂ source (V1). In V2, the highest CO₂ utilization efficiency was achieved (CO₂UE = 46.7 ± 2.4%). Analyzing the biomass composition confirmed differences in total carbon content (TC) and polysaccharide fraction. The highest H₂ production efficiency and rate, which were 70.9 ± 2.7 mL/gVS and 2.27 ± 0.08 mL/gVS·h, respectively, were obtained in V2. The results obtained indicate the possibility of integrating fuel combustion processes with the cultivation of T. subcordiformis and photobiological H₂ production, which is a promising solution in the context of climate neutrality and the implementation of circular economy postulates. This approach demonstrates a sustainable strategy for linking industrial CO₂ emissions with the production of renewable biohydrogen and thus contributes to climate protection and the promotion of circular economy concepts. Full article

Dark fermentation (DF) has gained increasing interest over the past two decades as a sustainable route for biohydrogen production; however, understanding how reproducible the process can be, both from macro- and microbiological perspectives, remains limited. This study assessed the reproducibility of a parallel continuous DF system using fruit-vegetable waste as a substrate under strictly controlled operational conditions. Three stirred-tank reactors were operated in parallel for 90 days, monitoring key process performance indicators. In addition to baseline operation, different process enhancement strategies were tested, including bioaugmentation, supplementation with nutrients and/or additional fermentable carbohydrates, and modification of key operational parameters such as pH and hydraulic retention time, all widely used in the field to improve DF performance. Microbial community structure was also analyzed to evaluate its reproducibility and potential relationship with process performance and metabolic patterns. Under these conditions, key performance indicators and core microbial features were reproducible to a large extent, yet full consistency across reactors was not achieved. During operation, unforeseen operational issues such as feed line clogging, pH control failures, and mixing interruptions were encountered. Despite these disturbances, the system maintained an average hydrogen productivity of 3.2 NL H₂/L-d, with peak values exceeding 6 NL H₂/L-d under optimal conditions. The dominant microbial core included Bacteroides, Lactobacillus, Veillonella, Enterococcus, Eubacterium, and Clostridium, though their relative abundances varied notably over time and between reactors. An inverse correlation was observed between lactate concentration in the fermentation broth and the amount of hydrogen produced, suggesting it can serve as a precursor for hydrogen. Overall, the findings presented here demonstrate that DF processes can be resilient and broadly reproducible. However, they also emphasize the sensitivity of these processes to operational disturbances and microbial shifts. This underscores the necessity for refined control strategies and further systematic research to translate these insights into stable, high-performance real-world systems. Full article

Biohydrogen, a low-carbon footprint technology, can play a significant role in decarbonizing the energy system. It uses existing infrastructure, is easily transportable, and produces no greenhouse gas emissions. Four technologies can be used to produce biohydrogen: photosynthetic biohydrogen, dark fermentation (DF), photo-fermentation, and microbial electrolysis cells (MECs). DF produces more biohydrogen and is flexible with organic substrates, making it a sustainable method of waste repurposing. However, low achievable biohydrogen yields are a common issue. To overcome this, catalytic mechanisms, including enzymatic systems such as [Fe-Fe]- and [Ni-Fe]-hydrogenases in DF and electroactive microbial consortia in MECs, alongside advanced electrode catalysts which collectively surmount thermodynamic and kinetic constraints, and the two stage system, such as DF connection to photo-fermentation and anaerobic digestion (AD) to microbial electrolysis cells (MECs), have been investigated. MECs can generate biohydrogen at better yields by using sugars or organic acids, and combining DF and MEC technologies could improve biohydrogen production. As such, this review highlights the challenges and possible solutions for coupling DF–MEC while also offering knowledge regarding the technical and microbiological aspects. Full article

Hydrogen is key to achieving a net-zero carbon future, yet current production remains predominantly fossil-based. Biohydrogen derived from agricultural residues represents a sustainable alternative aligned with circular economy principles. While several studies have assessed the bioenergy potential from agricultural residues in various African countries, their potential in Togo remains largely unexplored. This study employed an exploratory mixed-methods approach to quantify residue availability, evaluate production pathways, and estimate potential biohydrogen yields. Secondary data on crop production from the Food and Agriculture Organization (FAO) and theoretical conversion factors were used to assess the availability of agricultural residues from the eight major crops in Togo, resulting in a residue potential of 7.95 million tons per year. Considering ecological and competing aspects of residue utilization, a sustainable share of 3.1 to 6.6 million tons was estimated to be available for biohydrogen production, depending on the residue recoverability assumptions. A multi-criteria decision analysis (MCDA) was used to evaluate different biohydrogen production processes, identifying dark fermentation as the most suitable due to its low energy requirements and decentralized applicability. The theoretical biohydrogen potential was estimated at 20,991–42,293 tons per year (2.5–5.1 PJ per year) based on biochemical residue composition data and stoichiometric calculations. This study established a baseline assessment of biohydrogen potential from agricultural residues in Togo, offering a methodological framework for assessing biohydrogen potential in other regions. The results also underscore the need for site-specific data to reduce uncertainty and support evidence-based energy planning. Full article

This study examines the enhancement of dark sequential fermentation and photofermentation of organic solid waste using magnetite and substrate pre-treatment for hydrogen production within the context of transitioning to cleaner energy sources, particularly low-carbon hydrogen. Experimental dark fermentation and photofermentation apparatuses were used, utilizing microorganisms to decompose biomass at a mesophilic temperature (35 °C) of Organic Fraction of Municipal Solid Waste (OFMSW), inoculated with UASB sludge and enhanced with magnetite. A dosage of 120 mg/L of magnetite was the most effective, yielding an average value of 4144 mL H₂/gVS. Additionally, the analysis revealed that the levelized cost of hydrogen (LCOH) decreases as more organic waste is utilized, making biohydrogen production a sustainable option, reaching USD 5/kg of OFMSW. Ultimately, generating hydrogen from organic waste can help reduce greenhouse gas emissions and promote a cleaner energy matrix. Full article

This study explores the sequential valorization of orange peel waste (OPW) through photo-fermentation using real dark fermentation effluents (DFE) as substrates for hydrogen production using Rhodobacter capsulatus B10. Three DFE types—differing in prior biocompound extraction method—and their concentrations at three levels (25, 35, and 45%) were evaluated. The highest hydrogen yield (126.5 mL H₂ g⁻¹ VFA) was achieved with DFE derived from essential oil-extracted OPW at a concentration of 25%. The highest DFE concentration reduced the hydrogen yield due to intensified medium opacity and potential substrate inhibition. Kinetic modeling revealed that the Modified Gompertz and T_i-Gompertz models best described hydrogen production dynamics. This study presents the first evidence of hydrogen production via photo-fermentation using real effluents derived from OPW processing, demonstrating a novel route for citrus waste reuse within a biorefinery framework. These findings underscore the innovation and relevance of integrating waste valorization with clean energy production, while also identifying key operational challenges to be addressed. Full article

Bio-hydrogen and bio-methane co-production was a promising way to enhance the energy conversion efficiency, and enzyme loading and pH are key factors influencing anaerobic fermentation processes. Therefore, in this study, the co-production process of bio-hydrogen and bio-methane was evaluated based on the effect of enzyme loading (20%, 30%, and 40%) combined with initial pH (6.0, 7.0, 8.0, and 9.0). The results indicated that, compared with other conditions, 30% enzyme loading with an initial pH of 8.0 was more feasible for bio-hydrogen and bio-methane co-production from duckweed, achieving a bio-hydrogen yield of 114.56 mL/g total solid (TS) and a bio-methane yield of 260.32 mL/g TS. Under optimum condition, the energy conversion efficiency was 71.4%, which was 6-fold and 4.8-fold higher than that of the single bio-hydrogen production stage (pH 8, 40% and 10.2%) and single methane production stage (control group with 12.30%), respectively. Full article

The citrus processing industry is an economically important agro-industrial sector worldwide; however, it produces significant amounts of waste annually. The biorefinery concept and the recovery of bio-based materials from agro-industrial residues, including citrus processing waste, are emphasized in the European Green Deal, reflecting the EU’s commitment to fostering circularity. Biotreatment of citrus processing waste, including bioconversion into biomethane, biohydrogen, bioethanol and biodiesel, has been applied to valorize biomass for energy recovery. It can also be composted into a valuable soil conditioners and fertilizers, while raw and fermented citrus residues may exhibit phytoprotective activity. Citrus-derived residues can be converted into materials such as nanoparticles with adsorptive capacity for heavy metals and recalcitrant organic pollutants, and materials with antimicrobial properties against various microbial pathogens, or the potential to remove antibiotic-resistance genes (ARGs) from wastewater. Indeed, citrus residues are an ideal source of industrial biomolecules, like pectin, and the recovery of bioactive compounds with added value in food processing industry. Citrus processing waste can also serve as a source for isolating specialized microbial starter cultures or as a substrate for the growth of bioplastic-producing microorganisms. Solid-state fermentation of citrus residues can enhance the production of hydrolytic enzymes, with applications in food and environmental technology, as well as in animal feed. Certain fermented products also exhibit antioxidant properties. Citrus processing waste may be used as alternative feedstuff that potentially improves the oxidative stability and quality of animal products. Full article

MFD is a nutritional disorder in dairy cattle characterized by a reduction in milk fat content despite a normal or increased milk yield. This review synthesizes current knowledge on the biological mechanisms and nutritional factors contributing to the development of this condition. Disruptions in rumen fermentation and alterations in fatty acid biohydrogenation (particularly the formation of trans-10 fatty acids) are recognized as central contributors to MFD. Several theories have been proposed to explain its pathophysiology, including the glucogenic, volatile fatty acid, trans fatty acid, and biohydrogenation theories. MFD is most commonly associated with diets low in fiber and high in polyunsaturated fatty acids or starch, which promote the accumulation of fatty acid intermediates that inhibit mammary lipogenesis. Among these, trans-10, cis-12 conjugated linoleic acid is particularly notable for its potent suppression of de novo fatty acid synthesis in the mammary gland. While proper dietary formulation remains the most effective preventive strategy, nutritional interventions such as magnesium-based alkalinizers, sodium bicarbonate, intravenous arginine, and vitamin E have shown promise in mitigating established cases. This review underscores the importance of nutritional management in preserving milk fat synthesis and promoting overall animal health. Full article

Anaerobic digestion (AD) has long been valued for producing a biogas–digestate pair, yet its profitability is tightening. Next-generation AD biorefineries now position syngas both as a supplementary feedstock and as a springboard to capture high-value intermediates, hydrogen (H₂) and volatile fatty acids (VFA). This review dissects how complex natural consortia “decide” between hydrogenogenesis and acetogenesis when CO, H₂, and CO₂ co-exist in the feedstocks, bridging molecular mechanisms with process-scale levers. The map of the bioenergetic contest between the biological water–gas shift reaction and Wood–Ljungdahl pathways is discussed, revealing how electron flow, thermodynamic thresholds, and enzyme inhibition dictate microbial “decision”. Kinetic evidence from pure and mixed cultures is integrated with practical operating factors (gas composition and pressure, pH–temperature spectrum, culture media composition, hydraulic retention time, and cell density), which can bias consortia toward the desired product. Full article

Various pretreatment methods for the valorization of sunflower husks (SHs) for H₂ gas generation through fermentation by Escherichia coli were investigated. We analyzed thermal treatment (TT), acid hydrolysis (AH), and alkaline hydrolysis (AlkH) at different substrate concentrations (50 g L⁻¹, 75 g L⁻¹, 100 g L⁻¹, and 150 g L⁻¹) and dilution levels (undiluted, 2× diluted, and 5× diluted). A concentration of 75 g L⁻¹ SH that was acid-hydrolyzed and dissolved twice in the medium yielded optimal microbial growth, reaching 0.3 ± 0.1 g cell dry weight (CDW) L⁻¹ biomass. The highest substrate level enabling effective fermentation was 100 g L⁻¹, producing 0.37 ± 0.13 (g CDW) × L⁻¹ biomass after complete fermentation, while 150 g L⁻¹ exhibited pronounced inhibitory effects. It is worth mentioning that the sole alkaline treatment was not optimal for growth and H₂ production. Co-fermentation with glycerol significantly enhanced both biomass formation (up to 0.42 ± 0.15 (g CDW) × L⁻¹)) and H₂ production. The highest H₂ yield was observed during batch growth at 50 g L⁻¹ SH hydrolysate with 5× dilution, reaching up to 5.7 mmol H₂ (g sugar)⁻¹ with glycerol supplementation. This study introduces a dual-waste valorization strategy that combines agricultural and biodiesel industry residues to enhance clean energy generation. The novelty lies in optimizing pretreatment and co-substrate fermentation conditions to maximize both biohydrogen yield and microbial biomass using E. coli, a widely studied and scalable host. Full article

Anaerobic digestion is a widely adopted technique for biologically converting organic biomass to biogas under oxygen-limited conditions. However, several factors, including the properties of biomass and its complex structure, make it challenging to degrade biomass effectively, thereby reducing the overall efficiency of anaerobic digestion. This review examines the recent advancements in commonly used pretreatment techniques, including physical, chemical, and biological methods, and their impact on the biodegradability of organic waste for anaerobic digestion. Furthermore, this review explores integrated approaches that utilize two or more pretreatments to achieve synergistic effects on biomass degradation. This article highlights various additives and their physicochemical characteristics, which play a vital role in stimulating direct interspecies electron transfer to enhance biomethanation reaction rates. Direct electron interspecies transfer is a crucial aspect that accelerates electron transfer among syntrophic microbial communities during anaerobic digestion, thereby enhancing biomethane formation. Finally, this article reviews potential approaches, identifies research gaps, and outlines future directions to strengthen and develop advanced pretreatment strategies and novel additives to improve anaerobic digestion processes for generating high-value biogas. Full article

Adequate treatment of the organic fraction of municipal solid waste (OFMSW) in co-digestion with sewage sludge (SS) through dark fermentation (DF) technologies has been widely studied and recognized. However, there is little experience with a high-solids approach, where practical and scalable conditions are established to lay the groundwork for further development of feasible industrial-scale projects. In this study, the biochemical hydrogen potential of OFMSW using a 7 L batch reactor at mesophilic conditions was evaluated. Parameters such as pH, redox potential, temperature, alkalinity, total solids, and substrate/inoculum ratio were adjusted and monitored. Biogas composition was analyzed by gas chromatography. The microbial characterization of SS and post-reaction percolate liquids was determined through metagenomics analyses. Results show a biohydrogen yield of 38.4 NmLH₂/gVS OFMSW, which forms ~60% of the produced biogas. Aeration was proven to be an efficient inoculum pretreatment method, mainly to decrease the levels of methanogenic archaea and metabolic competition, and at the same time maintain the required total solid (TS) contents for high-solids conditions. The microbial community analysis reveals that biohydrogen production was carried out by specific anaerobic and aerobic bacteria, predominantly dominated by the phylum Firmicutes, including the genus Bacillus (44.63% of the total microbial community), Clostridium, Romboutsia, and the phylum Proteobacteria, with the genus Proteus. Full article

After a brief characterisation of lignocellulosic biomass (LCB) in terms of its biochemical structure and the pretreatment techniques used to disrupt lignin structure and decrystallise and depolymerise cellulose, this review considers five main pathways for biochemical biomass conversion: starting with anaerobic digestion to convert various LCB feedstocks into bioproducts; considering the integration of biochemical and thermochemical processes, syngas fermentation, which has been recently developed for biofuel and chemical production, is reviewed; the production of 2G bioethanol and biobutanol from LCB waste is discussed; the literature on biohydrogen production by dark fermentation, photofermentation, and bioelectrochemical processes using microbial electrolysis cells as well as hybrid biological processes is reviewed. The conclusions and future prospects of integrating biochemical and thermochemical conversion processes of biomass are discussed and emphasised. Full article