Comparison of mesophilic and thermophilic dark fermentation with nickel ferrite nanoparticles supplementation for biohydrogen production

Efficient carbon dioxide conversion by nickel ferrite-based catalysts derived from metallurgical electroplating sludge collaborating with low-temperature plasma

An innovative, environment-friendly, and efficient method was proposed for the synergistic low-temperature plasma conversion of CO2 by using nickel ferrite (NiFe2O4) catalyst. NiFe2O4, characterised by a mesoporous spinel structure, was successfully synthesised from electroplating sludge by a single-step heat treatment. The catalyst was uniformly distributed with SiO2 glass beads throughout the plasma discharge area, enabling an efficient transition from single filament to filament-surface coupled discharge. The outcomes were a 39.02 % increase in discharge charge and a 15 % increase in output power compared with plasma-only situation. CO2-conversion optimisation tests showed the formation of a 'microreaction zone' enhanced the development of gas vortices and turbulence, promoting the CO2-conversion ratio, CO generation ratio, and energy efficiency to 20.64 %, 15.74 %, and 1.864 %, respectively, under the NiFe2O4 catalyst-facilitated low-temperature plasma conditions. The conversion route involved generating excited-state CO, O2, and electrons through plasma ionisation of CO2, alongside the creation of oxygen vacancies (Vo). These vacancies regenerated by consuming lattice oxygen (O2-), facilitating CO2 convert to CO and O2 by electrons. Furthermore, the catalysts offered sites for adsorbing reaction intermediates, which further facilitated CO2 dissociation and product formation. The Fe and Ni ions in the NiFe2O4 catalyst reacted by redox to produce O2- and Vo and maintain charge equilibrium. This study demonstrated that the NiFe2O4 catalyst and synergistic plasma effectively converted CO2 whilst reducing the reaction's energy barrier, thereby providing theoretical support for improved CO2 utilisation as a resource.

Application of nanoparticles to increase biological hydrogen production: the difference in metabolic pathways in batch and continuous reactors

An alternative to improve the production of biorefinery products, such as biohydrogen (H2) and volatile fatty acids (VFA), is the combination of nanotechnology and biological processes. In order to compare the use of both processes in two different reactor configurations, batch reactors and continuous anaerobic fluidized bed reactors (AFBR) were studied under the same conditions (37°C, pH 6.8, Clostridium butyricum as an inoculum and glucose as a substrate) to evaluate the influence of zero valence iron and nickel nanoparticles (NPs) on H2 and VFA production. There was a shift in the production of acetic and butyric acids to produce mainly valeric acid when NPs were added in batch reactors. Meanwhile, in AFBR the change was from lactic acid to butyric and acetic acids with the addition of NPs. It showed that the effect of NPs on the fermentation process was different when the configuration of batch and continuous reactors was compared. The H2 yield in both reactor configurations increased with the addition of NPs. In batch reactors from 6.6 to 8.0 mmol H2 g-1 of COD and in AFBR from 4.9 to 6.2 mmol of H2 g-1 of COD. Therefore, given the simplicity and low cost of the synthesis of metallic NPs, it is a promising additive to optimize the fermentation process in different reactor configurations.

Light energy utilization and microbial catalysis for enhanced biohydrogen: Ternary coupling system of triethanolamine-mediated Fe@C-Rhodobacter sphaeroides

This study investigated the mediating effect of Triethanolamine on Fe@C-Rhodobacter sphaeroides hybrid photosynthetic system to achieve efficient biohydrogen production. The biocompatible Fe@C generates excited electrons upon exposure to light, releasing ferrum for nitrogenase synthesis, and regulating the pH of the fermentation environment. Triethanolamine was introduced to optimize the electron transfer chain, thereby improving system stability, prolonging electron lifespan, and facilitating ferrum corrosion. This, in turn, stimulated the lactic acid synthetic metabolic pathway of Rhodobacter sphaeroides, resulting in increased reducing power in the biohybrid system. The ternary coupling system was analyzed through the regulation of concentration, initial pH, and light intensity. The system achieved the highest total H2 production of 5410.9 mL/L, 1.29 times higher than the control (2360.5 mL/L). This research provides a valuable strategy for constructing ferrum-carbon-based composite-cellular biohybrid systems for photo-fermentation H2 production.

Enhancing biohydrogen production from xylose through natural FeS2 ore: Mechanistic insights

In this study, we investigated the advantages of utilizing natural FeS2 ore in the context of dark fermentative hydrogen production within a fermentation system employing heat-treated anaerobic granular sludge with xylose as the carbon source. The results demonstrated a significant improvement in both hydrogen production and the maximum rate, with increases of 2.58 and 4.2 times, respectively. Moreover, the presence of FeS2 ore led to a reduction in lag time by more than 2-3 h. The enhanced biohydrogen production performance was attributed to factors such as the intracellular NADH/NAD+ ratio, redox-active components of extracellular polymeric substances, secreted flavins, as well as the presence of hydrogenase and nitrogenase. Furthermore, the FeS2 ore served as a direct electron donor and acceptor during biohydrogen production. This study shed light on the underlying mechanisms contributing to the improved performance of biohydrogen production from xylose during dark fermentation through the supplementation of natural FeS2 ore.

A bibliometric analysis of the role of nanotechnology in dark fermentative biohydrogen production

Recently, nanoparticles have drawn a lot of interest as catalysts to enhance the effectiveness and output of biohydrogen generation processes. This review article provides a comprehensive bibliometric analysis of the significance of nanotechnology in dark fermentative biohydrogen production. The study examines the scientific literature from the database of The Web of Science© while the bibliometric investigation utilized VOSviewer© and Bibliometrix software tools to conduct the analysis. The findings revealed that a total of 232 articles focused on studying dark fermentation for hydrogen production throughout the entire duration. The extracted data was used to analyze publication trends, authorship patterns, and geographic distribution along with types and effects of nanoparticles on the microbial community responsible for dark fermentative biohydrogen production. The findings of this bibliometric analysis provide valuable insights into the advancements and achievements in the utilization of nanoparticles in the dark fermentation process used to produce biohydrogen.

Enhanced thermophilic dark fermentation of hydrogen production from food waste by Fe-modified biochar

The industrialization of hydrogen production through dark fermentation of food waste faces challenges, such as low yields and unpredictable fermentation processes. Biochar has emerged as a promising green additive to enhance hydrogen production in dark fermentation. Our study demonstrated that the introduction of Fe-modified biochar (Fe-L600) significantly boosted hydrogen production during thermophilic dark fermentation of food waste. The addition of Fe-L600 led to a remarkable 31.19% increase in hydrogen yield and shortened the time needed for achieving stabilization of hydrogen production from 18 h to 12 h. The metabolite analysis revealed an enhancement in the butyric acid pathway as the molar ratio of acetic acid to butyric acid decreased from 3.09 to 2.69 but hydrogen yield increased from 57.12 ± 1.48 to 76.78 ± 2.77 mL/g, indicating Fe-L600 improved hydrogen yield by regulating crucial metabolic pathways of hydrogen production. The addition of Fe-L600 also promoted the release of Fe2+ and Fe3+ and increased the concentrations of Fe2+ and Fe3+ in the fermentation system, which might promote the activity of hydrogenase and ferredoxin. Microbial community analysis indicated a substantial increase in the relative abundance of Thermoanaerobacterium after thermophilic dark fermentation. The relative abundances of microorganisms responsible for hydrolysis and acidogenesis were also observed to be improved in the system with Fe-L600 addition. This research provides a feasible strategy for improving hydrogen production of food waste and deepens the understanding of the mechanisms of biochar.

Enhanced membrane fouling by microplastics during nanofiltration of secondary effluent considering secretion, interaction and deposition of extracellular polymeric substances

Microplastic (MP) has been found to influence membrane fouling during microfiltration/ultrafiltration processes in direct and indirect ways by acting as fouling components and changing microbial activities, respectively. However, there is no relevant research about the contribution of MPs to nanofiltration membrane fouling. In this study, for the first time, the impacts of MPs on membrane fouling during the nanofiltration of secondary effluent (SE) were systematically investigated from the perspective of bacterial extracellular polymeric substances (EPS) secretion, their interaction with coexisting pollutants and also deposition. Membrane flux behaviors indicate that MPs simultaneously aggravated the short-term and long-term membrane fouling resistance of nanofiltration by 46 % and 27 %, respectively. ATR-FTIR, XPS and spectrophotometry spectra demonstrate that the deteriorated membrane fouling by MPs directly resulted from the increased accumulation of protein-like, polysaccharides-like and humic-like substances on membranes. EEM spectra further confirmed that MPs preferred to induce serious cake layers, which dominated membrane flux decline but hindered pore fouling. According to CLSM and SEM-EDS mappings, MPs in SE could stimulate microbial activities and then aggravate EPS secretion, after which their interaction with Ca2+ was also enhanced in bulk solution. The cross-linker nets could promote the deposition of other unlinked pollutants on membranes. Besides, MPs could weaken the rejection of certain dissolved organic matters (from 57 % to 52 % on the 50th day of filtration) by aggravating cake-enhanced concentration polarization (CECP), but improved the average removal of inorganic salts from 58 % to 63 % by improving their back diffusion through cake layers. Based on these analyses, the mechanisms of MP-enhanced membrane fouling during the nanofiltration of SE can be thoroughly revealed.

Comparative effect of acid and heat inoculum pretreatment on dark fermentative biohydrogen production

This study delves into the impact of various pretreatment methods on the inoculum in dark fermentation trials, specifically exploring thermal shock at different temperatures (60, 80, and 100 °C) and durations (15, 30, and 60 min), as well as acid shock at pH 5.5. Initial acidification of the substrate/inoculum mixture facilitates H2 generation, making acid shock an effective pretreatment option. However, it is also observed that combining thermal and acid pretreatments boosts H2 production synergistically. The synergy between thermal and acid pretreatments results in a significant improvement, increasing the overall hydrogen production efficiency by more than 9% compared to assays involving acidification alone. This highlights the considerable potential for optimizing pretreatment strategies. Furthermore, the study sheds light on the critical role of inoculum characteristics in the process, with diverse hydrogen-generating bacteria significantly influencing outcomes. The established equivalent performance of HCl and H2SO4 in inoculum pretreatment demonstrates the versatility of these acids in shaping the microbial community and influencing hydrogen production. The analysis of glucose conversion data highlights a prevalence of butyric acid in all trials, irrespective of the pretreatment method, emphasizing the dominance of the butyrate pathway in hydrogen generation. Additionally, an examination of the microbial community offers valuable insights into the intricate relationships between temperature, pH, and microbial diversity. Bacteroidota established its dominance among the bacterial populations, with a relative abundance exceeding 20-25% in the raw inoculum, and this dominance further increased following the treatment. Thermal and acid pretreatments result in significant shifts in dominant microbial communities, with some non-dominant phyla like Cloacimonadota and Spirochaetota becoming more prominent. These shifts in microbial diversity underscore the sensitivity of microbial communities to environmental conditions and pretreatment methods, further highlighting the importance of understanding their dynamics in dark fermentation processes.

Nanotechnology based technological development in biofuel production: Current status and future prospects

Depleting fossil fuels and net carbon emissions associated with their burning have driven the need to find alternative energy sources. Biofuels are near-perfect candidates for alternative energy sources as they are renewable and account for no net CO2 emissions. However, biofuel production must overcome various challenges to compete with conventional fuels. Conventional methods for bioconversion of biomass to biofuel include chemical, thermochemical, and biological processes. Substrate selection and processing, low yield, and total cost of production are some of the main issues associated with biofuel generation. Recently, the uses of nanotechnology and nanoparticles have been explored to improve the biofuel production processes because of their high adsorption, high reactivity, and catalytic properties. The role of these nanoscale particles and nanocatalysts in biomass conversion and their effect on biofuel production processes and yield are discussed in the present article. The applicability of nanotechnology in production processes of biobutanol, bioethanol, biodiesel, biohydrogen, and biogas under biorefinery approach are presented. Different types of nanoparticles, and their function in the bioprocess, such as electron transfer, pretreatment, hydrolysis, microalgae cultivation, lipid extraction, dark and photo fermentation, immobilization, and suppression of inhibitory compounds, are also highlighted. Finally, the current and potential applications of nanotechnology in biorefineries are also discussed.

Unraveling the mechanism of increased synthesis of hydrogen from an anaerobic fermentation by zinc ferrate nanoparticles: Mesophilic and thermophilic situations comparison

In this work, ZnFe2O4 NPs were created using the pyrolysis process, and its effects on thermophilic (TF) and mesophilic (MF) fermentation were examined. In MF, the maximum hydrogen yield (MHY) occurred in the 50 mg/L ZnFe2O4 NPs group (228.01 mL/g glucose), which was 45.24% higher than that of the control group (157.01 mL/g glucose). While in TF, MHY appeared in 100 mg/L ZnFe2O4 NPs was 149.12 mL/g glucose, which was 38.83% higher than the control group (107.41 mL/g glucose). ZnFe2O4 NPs boosted the synthesis of ferredoxin, hydrogenase, and ethanol dehydrogenase by increasing the generation of butyrate in MF and acetate in TF. Moreover, Clostridium sensu stricto 5 and 10 in MF and TF rose by 9.20% and 9.40%, respectively, due to the increased abundance of predominant hydrogen-producing bacteria by ZnFe2O4 NPs.

Extracellular self-photosensitizer combined with metal oxide-based nano bio-hybrid system encapsulated by alginate improves hydrogen production in the presence of oxygen

The photocatalytic nano-biohybrid systems have great potential for the conversion of solar energy to fermentative hydrogen production. Herein, a whole-cell nano-biohybrid system consisting of biosynthesized cadmium sulfide, Enterobacter aerogenes cells, and metal oxide nanoparticles was constructed. The system was encapsulated with sodium alginate and used for light-driven biohydrogen production under anaerobic and in the presence of oxygen conditions. After 48 h incubation in the presence of oxygen, the E. aerogenes cells with the encapsulated hybrid system yielded 2.7 mmol H2/mmol glucose, a 13.5-fold higher than that of the E. aerogenes cells without encapsulation. The encapsulated hybrid system could produce hydrogen for up to 96 h and could produce hydrogen even under natural sunlight conditions. These results revealed that efficient hydrogen production is possible in the presence of oxygen. Overall, the present study demonstrated the potential of using proper nano-biohybrid system with encapsulation for the production of hydrogen under ambient air condition.

Influence of iron and magnesium on kinetic and mechanism of biohydrogen production from high-strength wastewater

In this study, iron/iron-magnesium (Fe/Fe-Mg) additives were prepared through the impregnation of granular activated carbon (GAC) with iron and iron-magnesium (GFM) to enhance biohydrogen production. The microscope observation and chemical analysis revealed that the GAC matrixes were well infused with Fe/Fe-Mg, while the X-ray diffraction analysis revealed the species of metal formed on the GAC as Fe3+ and MgH2. The synergistic effect of Fe and Mg in GFM allowed it for a shorter delay time and higher hydrogen production rate than other additives, indicating their possible use in stimulating the fast release of hydrogen in anaerobic digestion. The co-metabolites analysis revealed that additives ensured biohydrogen production through the different pathways. The plausible mechanisms were through hydrogenases ensured by Fe3+ and hydrolysis by MgH2. GFM gave the best organic matter and nutrient removal efficiency to outperform other additives, suggesting its ability for biohydrogen synthesis and simultaneous wastewater treatment.

Magnetic nitrogen-doped activated carbon improved biohydrogen production

Low biological hydrogen (bioH2) production due to non-optimal metabolic pathways occurs frequently. In this work, magnetic nitrogen-doped activated carbon (MNAC) was prepared and added into the inoculated sludge with glucose as substrate to enhance hydrogen (H2) yield by mesophilic dark fermentation (DF). The highest H2 yield appeared in 400 mg/L AC (252.8 mL/g glucose) and 600 mg/L MNAC group (304.8 mL/g glucose), which were 26.02% and 51.94% higher than that of 0 mg/L MNAC group (200.6 mL/g glucose). The addition of MNAC allowed for efficient enrichment of Firmicutes and Clostridium-sensu-stricto-1, accelerating the metabolic pathway shifted towards butyrate type. The Fe ions released by MNAC facilitated electron transfer and favored the reduction of ferredoxin (Fd), thereby obtaining more bioH2. Finally, the generation of [Fe-Fe] hydrogenase and cellular components of H2-producing microbes (HPM) during homeostasis was discussed to understand on the use of MNAC in DF system.

Triggering photo fermentative biohydrogen production through NiFe2O4 photo nanocatalysts with various excitation sources

The triggering effects of nickel ferrite (NiFe₂O₄) photo nanocatalysts on photo fermentative hydrogen production (PFHP), and metabolic pathways under various excitation sources (incandescent lamp, Xenon lamp, and 532 laser) have been investigated. Compare to the control group (CG) highest cumulative hydrogen volume (CHV) and the maximum hydrogen production rate (HPR) of 568.8 mL and 9.17 mL/h, respectively were achieved at a loading centration of 150 mg/L excited with an incandescent lamp. The change in metabolites with NiFe₂O₄ incorporation suggests that bacterial activity is significantly affected by photo nanocatalysts. Triggering of NiFe₂O₄ by laser excitation showed the highest HPR of 7.83 mL /h within 24 h, which greatly reduces the lag time. The microbial community investigation showed that the addition of NiFe₂O₄ photo nanocatalysts and the change of light source effectively improved the microbial community structure and increased the abundance of hydrogen-producing bacteria (HPB) which leads to enhanced hydrogen production.

Hydrothermal carbon microspheres and their iron salt modification for enhancing biohydrogen production

Dark fermentation (DF) for hydrogen (H₂) evolution is often limited to industrial application due to its low H₂ yield. In this work, hydrothermal carbon microspheres (HCM) and iron modified HCM (Fe-HCM) were prepared by hydrothermal process using waste corn cob. Subsequently, HCM and Fe-HCM were used in DF for more H₂. The highest H₂ yields amended with HCM and Fe-HCM at 600 mg/L were achieved to be 119 and 154 mL/g glucose (0.87 and 1.2 mol H₂/mol glucose), respectively, being 24% and 59% higher than that of control yield. Soluble metabolites revealed HCM and Fe-HCM promoted butyric acid-based DF. Microbial composition depicted that HCM and Fe-HCM improved the abundance level of Firmicutes from 35% to 41% and 56%, while the abundance level of Clostridium_sensu_stricto_1 rose from 25% to 38% and 51%, respectively. This provides valuable guidance for hydrothermal carbon used in biofuel production.

Epitomizing biohydrogen production from microbes: Critical challenges vs opportunities

Hydrogen is a clean and green biofuel choice for the future because it is carbon-free, non-toxic, and has high energy conversion efficiency. In exploiting hydrogen as the main energy, guidelines for implementing the hydrogen economy and roadmaps for the developments of hydrogen technology have been released by several countries. Besides, this review also unveils various hydrogen storage methods and applications of hydrogen in transportation industry. Biohydrogen productions from microbes, namely, fermentative bacteria, photosynthetic bacteria, cyanobacteria, and green microalgae, via biological metabolisms have received significant interests off late due to its sustainability and environmentally friendly potentials. Accordingly, the review is as well outlining the biohydrogen production processes by various microbes. Furthermore, several factors such as light intensity, pH, temperature and addition of supplementary nutrients to enhance the microbial biohydrogen production are highlighted at their respective optimum conditions. Despite the advantages, the amounts of biohydrogen being produced by microbes are still insufficient to be a competitive energy source in the market. In addition, several major obstacles have also directly hampered the commercialization effors of biohydrogen. Thus, this review uncovers the constraints of biohydrogen production from microbes such as microalgae and offers solutions associated with recent strategies to overcome the setbacks via genetic engineering, pretreatments of biomass, and introduction of nanoparticles as well as oxygen scavengers. The opportunities of exploiting microalgae as a suastainable source of biohydrogen production and the plausibility to produce biohydrogen from biowastes are accentuated. Lastly, this review addresses the future perspectives of biological methods to ensure the sustainability and economy viability of biohydrogen production.

Nickel-Cobalt Oxide Nanoparticle-Induced Biohydrogen Production

The positive effects of metal oxide nanoparticles (NPs) on dark fermentation (DF) for biohydrogen synthesis have been increased, and the mechanism still needs to be further revealed. In this study, nickel-cobalt oxide (NiCo₂O₄) NPs were prepared to increase H₂ yield via DF. The highest (259.67 mL/g glucose) and the lowest (188.14 mL/g glucose) yields were achieved at 400 and 800 mg/L NiCo₂O₄ NPs added, respectively, with their corresponding 33.97% increase and 2.93% decrease compared with the control yield (193.82 mL/g glucose). Meanwhile, the microbial community further confirmed that NiCo₂O₄ NPs increased the abundance of the dominant H₂-producing Clostridium sensu stricto 1 by 23.05%. The gene prediction also showed that NiCo₂O₄ NPs increased the abundance of genes encoding the rate-limiting enzyme pyruvate kinase in glycolysis, thus increasing the substrate conversion. Moreover, the gene abundance of key enzymes directly related to H₂ evolution was also increased at different levels.

Thermophilic biohydrogen production strategy using agro industrial wastes: Current update, challenges, and sustainable solutions

Continuously increasing wastes management issues and the high demand of fuels to fulfill the current societal requirements is not satisfactory. In addition, severe environmental pollution caused by generated wastes and the massive consumption of fossil fuels are the main causes of global warming. In this scenario, production of hydrogen from organic wastes is a potential and one of the most feasible alternatives to resolve these issues. However, sensitivity of H₂ production at higher temperature and lack of potential substrates are the main issues which are strongly associated with such kinds of biofuels. Therefore, the present review is targeted towards the evaluation and enhancement of thermophilic biohydrogen production using organic, cellulosic wastes as promising bioresources. This review discusses about the current status, development in the area of thermophilic biohydrogen production wherein organic wastes as key substrate are being employed. The combinations of suitable organic and cellulose rich substrates, thermo-tolerant microbes, high enzymes stability may support to enhance the biohydrogen production, significantly. Further, various factors which may significantly contribute to enhance biohydrogen production have been discussed thoroughly in reference to the thermophilic biohydrogen production technology. Additionally, existing obstacles such as unfavorable thermophilic biohydrogen pathways, inefficiency of thermophilic microbiomes, genetic modifications, enzymes stability have been discussed in context to the possible limitations of thermophilic biohydrogen production strategy. Structural and functional microbiome analysis, fermentation pathway modifications via genetic engineering and the application of nanotechnology to enhance the thermophilic biohydrogen production have been discussed as the future prospective.

Screening of the heterotrophic microalgae strain for the reclamation of acid producing wastewater

For the sustainable development of the environment, to reduce the high cost and low productivity of microalgae biofuel, nine microalgae strains were screened to study the growh and nutrient removal properties under heterotrophic culture by using the waste carbon source of volatile fatty acids (VFAs). Chlorella sorokiniana (C.sorokiniana) was selected as the best strain with the highest biomass concentration of 0.77 g L^-1, specific growth rate of 0.25 d^-1, biomass productivity of 91.43 mg L^-1 d^-1, total nitrogen removal efficiency of 95.96% and total phosphorus removal efficiency of 93.42%. To study the utilization potential of acid-producing wastewater by heterotrophic microalgae, actual acid-producing wastewater was recycled three times for the utilization of C.sorokiniana. After the three utilization cultivation, the removal rates of COD, total nitrogen, ammonia nitrogen, and total phosphorus were 74.44%, 88.05%, 79.08%, and 82.69%, respectively. The total utilization rates of acetic acid, propionic acid, and butyric acid were 58.99%, 70.54%, and 81.52%, respectively. In addition, the highest lipid content of 39.15% and protein content of 42.43% achieved at the third cultivation. After the first cultivation, the composition and diversity of the microbial community structure changed dramatically, with Protebacteria, Bacteroidota, Hydrogenophaga, and Algoriphagus becoming enriched. These results showed a promising way of coupling wastewater treatment with biomass production for long-term sustainability of microalgae lipid production.

Biohydrogen production and purification: Focusing on bioelectrochemical systems

Innovative technologies on green hydrogen production become significant as the hydrogen economy has grown globally. Biohydrogen is one of green hydrogen production methods, and microbial electrochemical cells (MECs) can be key to biohydrogen provision. However, MECs are immature for biohydrogen technology due to several limitations including extracellular electron transfer (EET) engineering. Fundamental understanding of EET also needs more works to accelerate MEC commercialization. Interestingly, studies on biohydrogen gas purification are limited although biohydrogen gas mixture requires complex purification for use. To facilitate an MEC-based biohydrogen technology as the green hydrogen supply this review discussed EET kinetics, engineering of EET and direct interspecies electron transfer associated with hydrogen yield and the application of advanced molecular biology for improving EET kinetics. Finally, this article reviewed biohydrogen purification technologies to better understand purification and use appropriate for biohydrogen, focusing on membrane separation.

Effects of metronidazole on mesophilic and thermophilic fermentation: Biodegradation mechanisms, microbial communities, and reversibility

Metronidazole (MNZ), an antibiotic that is specifically used for the treatment of anaerobic infections, may inhibit anaerobic fermentation. This work was designed to understand the fate and effects of MNZ in mesophilic fermentation (MF) and thermophilic fermentation (TF), respectively. The results showed that the removal of MNZ mainly occurred via biodegradation, rather than adsorption, and that MNZ could be completely degraded by opening the imidazole ring. MFs were more strongly inhibited by MNZ than TFs. MNZ concentration increased from 0 to 25 mg/L, hydrogen yield (HY) decreased from 167.5 to 16.8 mL/g glucose (90.0% decrease), and butyrate yield almost completely disappeared in MFs, whereas in TFs, HY decreased only from 101.1 to 89.3 mL/g glucose (11.7% decrease), and ethanol yield increased by 39.8%. Illumina MiSeq sequencing analysis showed that MNZ reduced the abundance of hydrogen-producing bacteria. Furthermore, the inhibition of MNZ on anaerobic fermentation was reversible.

The enhancement on biohydrogen production by the driving forces from extracellular iron oxide respiration

Biohydrogen productions from xylose and glucose under dark condition were enhanced by the presence of natural Fe₃O₄. The electron equivalent of H₂ fractions accounted for 4.55 % and 5.69 % of the total given xylose and glucose in the experiments without Fe₃O₄, and that were correspondingly increased to 5.14 % and 6.50 % in the experiments with 100 mg/L of Fe₃O₄, respectively. Moreover, Fe₃O₄ increased the total intracellular NAD(H) concentrations by 8.84 % and 8.37 %, and boosted the ratios of NADH/NAD⁺ by 8.33 % and 17.72 % in xylose and glucose fermentation, respectively, comparing to the corresponding control experiments. The formation of electron couples of Fe(III)/Fe(II) during the iron oxide respiration and more generation of active extracellular polymeric substances components were determined as the important reasons for the improved biohydrogen production performance. Thus, a promotion mechanism of the internal "driving forces" from extracellular iron oxide respiration on the biohydrogen production was proposed.

Improved biohydrogen evolution through calcium ferrite nanoparticles assisted dark fermentation

Dark fermentation (DF) is a green hydrogen (H₂) production process, but it is far below the theoretical H₂ yield. In this study, calcium ferrite nanoparticles (CaFe₂O₄ NPs) were produced to augment H₂ yield via DF. The highest H₂ yield of 250.1 ± 6.5 mL/g glucose was achieved at 100 mg/L CaFe₂O₄ NPs. Furtherincreasein CaFe₂O₄ NPs above 100 mg/L, such as 600 mg/L, would slightly lower H₂ yield to 208.6 ± 2.6 mL/g glucose. The CaFe₂O₄ NPs in DF system released calcium and iron ions, promoting granular sludge formation andDF microbial activity. Soluble metabolites revealed that butyric acid was raised by CaFe₂O₄ NPs, which indicated the improved metabolic pathway for more H₂. Microbial structure composition further illustrated that CaFe₂O₄ NPs could increase the abundance of dominant microbial populations, with the supremacy of Firmicutes up to 71.22 % in the bioH₂ evolution group augmented with 100 mg/L CaFe₂O₄ NPs.

Effect of metals on the regulation of acidogenic metabolism enhancing biohydrogen and carboxylic acids production from brewery spent grains: Microbial dynamics and biochemical analysis

The present study reports the mixed culture acidogenic production of biohydrogen and carboxylic acids (CA) from brewery spent grains (BSG) in the presence of high concentrations of cobalt, iron, nickel, and zinc. The metals enhanced biohydrogen output by 2.39 times along with CA biosynthesis by 1.73 times. Cobalt and iron promoted the acetate and butyrate pathways, leading to the accumulation of 5.14 gCOD/L of acetic and 11.36 gCOD/L of butyric acid. The production of solvents (ethanol + butanol) was higher with zinc (4.68 gCOD/L) and cobalt (4.45 gCOD/L). A combination of all four metals further enhanced CA accumulation to 42.98 gCOD/L, thus surpassing the benefits accrued from supplementation with individual metals. Additionally, 0.36 and 0.31 mol green ammonium were obtained from protein-rich brewery spent grain upon supplementation with iron and cobalt, respectively. Metagenomic analysis revealed the high relative abundance of Firmicutes (>90%), of which 85.02% were Clostridium, in mixed metal-containing reactors. Finally, a significant correlation of dehydrogenase activity with CA and biohydrogen evolution was observed upon metal addition.

Effect of Ammoniated Fiber Explosion Combined with H2O2 Pretreatment on the Hydrogen Production Capacity of Herbaceous and Woody Waste

An appropriate pretreatment process is an important part of the preparation of biomass energy from agricultural and forestry waste. Compared to physical and chemical pretreatments alone, the combined ammoniated fiber explosion (AFEX) + hydrogen peroxide (H₂O₂) pretreatment process can significantly improve the lignin degradation rate and saccharification efficiency, thus improving the hydrogen production capacity during medium-temperature dark fermentation. This study showed that the combined pretreatment increased the saccharification efficiency of herbaceous, hardwood, and softwood biomass by 58.7, 39.5, and 20.6% and the corresponding gas production reached 145.49, 80.75, and 57.52 mL/g, respectively. In addition, X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy showed that AFEX + H₂O₂ disrupted the structure of the feedstock and was more favorable for lignin removal. Soluble metabolites indicated that AFEX + H₂O₂ pretreatment enhanced the butyrate metabolic pathway of the substrate and biohydrogen generation and increased the levels of extracellular polymers and microbial community structure.

Unraveling the roles of lanthanum-iron oxide nanoparticles in biohydrogen production

Low hydrogen (H₂) yield via dark fermentation often occurs, being mainly due to H₂ generation pathway shift. In this study, lanthanum-iron oxide nanoparticles (LaFeO₃ NPs) were prepared to investigate their effects on bioH₂ production. The highest H₂ yield of 289.8 mL/g glucose was found at 100 mg/L of LaFeO₃, being 47.6% higher than that from the control (196.3 mL/g glucose). The relative abundance of Firmicutes increased from 54.2% to 67.5%. The large specific surface area of LaFeO₃ provided sufficient sites for the colonization of Firmicutes and increased the bacterial access to nutrients. Additionally, the La³⁺ gradually released from LaFeO₃ NPs raised microbial transmembrane transport capacity, promoting glycolytic efficiency and Fe availability, thereby increasing hydrogenase content, and shifting the bioH₂ evolution to butyrate pathway for more H₂. This provides the novelty for biochemical utilization of La and new insights into the improved H₂ yield amended with LaFeO₃.

Hydroxyapatite Fabrication for Enhancing Biohydrogen Production from Glucose Dark Fermentation

Hydroxyapatite (HA) had the effect of maintaining the pH balance of the reaction system and promoting enzyme activity. In this work, hydroxyapatite was synthesized by coprecipitation and characterized for biohydrogen (bioH₂) production from glucose. The highest bioH₂ yield obtained was 182.33 ± 2.41 mL/g glucose, amended with an optimal dosage of 400 mg/L HA, which was a 55.80% higher bioH₂ yield compared with the control group without any addition. The results indicated that HA facilitated the deterioration of organic substances and increased the concentration of soluble microbial products (SMPs). Microbial community analysis revealed that HA significantly increased the abundance of Firmicutes from 35.27% (0 mg/L, HA) to 76.41% (400 mg/L, HA), which played an essential role in bioH₂ generation. In particular, the abundance of Clostridium sensu stricto 1 increased from 15.33% (0 mg/L HA) to 45.17% (400 mg/L HA) and became the dominant bacteria. The results also indicated that HA likely improves bioH₂ production from organic wastewater in practice.

Biohydrogen production from microalgae for environmental sustainability

Hydrogen as a clean energy that is conducive to energy and environmental sustainability, playing a significant role in the alleviation of global climate change and energy crisis. Biohydrogen generation from microalgae has been reported as a highly attractive approach that can produce a benign clean energy carrier to achieve carbon neutrality and bioenergy sustainability. Thus, this review explored the mechanism of biohydrogen production from microalgae containing direct biophotolysis, indirect biophotolysis, photo fermentation, and dark fermentation. In general, dark fermentation of microalgae for biohydrogen production is relatively better than photo fermentation, biophotolysis, and microbial electrolysis, because it is able to consecutively generate hydrogen and is not reliant on energy supplied by natural sunlight. Besides, this review summarized potential algal strains for hydrogen production focusing on green microalgae and cyanobacteria. Moreover, a thorough review process was conducted to present hydrogen-producing enzymes targeting biosynthesis and localization of enzymes in microalgae. Notably, the most powerful hydrogen-producing enzymes are [Fe-Fe]-hydrogenases, which have an activity nearly 10-100 times better than [Ni-Fe]-hydrogenases and 1000 times better than nitrogenases. In addition, this work highlighted the major factors affecting low energy conversion efficiency and oxygen sensitivity of hydrogen-producing enzymes. Noting that the most practical pathway of biohydrogen generation was sulfur-deprivation compared with phosphorus, nitrogen, and magnesium deficiency. Further discussions in this work summarized the recent advancement in biohydrogen production from microalgae such as genetic engineering, microalgae-bacteria consortium, electro-bio-hydrogenation, and nanomaterials for developing enzyme stability and hydrolytic efficiency. More importantly, this review provided a summary of current limitations and future perspectives on the sustainable production of biohydrogen from microalgae.

Comparison of cobalt ferrate-based nanoparticles for promoting biomethane evolution from lactic acid anaerobic digestion

Some inhibition of biomethane (bioCH₄) production system can be observed, which is due to the propionic acid generation from lactic acid degradation. In this work, the three cobalt ferrate-based nanoparticles (NPs) such as CoFe₂O₄, CoAl_0.2Fe_1.8O₄ and CoCu_0.2Fe_1.8O₄ were synthesized to promote the bioCH₄ evolution from lactic acid. The CH₄ yields from the CoAl_0.2Fe_1.8O₄, CoCu_0.2Fe_1.8O₄ and CoFe₂O₄ groups at 300 mg/L of NPs were 431.52, 392.12 and 396.6 mL/g lactic acid, respectively. Moreover, the highest CH₄ yield was 34.15% higher than that of the control reactor (321.67 mL/g lactic acid) without NPs. The three NPs accelerated lactic acid biodegradation and propionic acid conversion, thus obtaining more CH₄. Surprisingly, microbial structure revealed that CoAl_0.2Fe_1.8O₄ increased the abundance of Bacteroidetes_vadinHA17 to 16.6%, promoting the conversion from propionic acid to acetic acid. Meanwhile, the abundance of Methanobacterium in archaeal community from CoAl_0.2Fe_1.8O₄ group rose from 45.81% to 68.45%, which facilitated bioCH₄ production.

Revealing the mechanisms of alkali-based magnetic nanosheets enhanced hydrogen production from dark fermentation: Comparison between mesophilic and thermophilic conditions

In the present study, a dark fermentation system inoculated with mixed culture bacteria (MCB) was developed using prepared alkali-based magnetic nanosheets (AMNSs) to facilitate biohydrogen (BioH₂) production. The highest BioH₂ yields of 232.8 ± 8.5 and 150.3 ± 4.8 mL/g glucose were observed at 100 (mesophilic condition) and 400 (thermophilic condition) mg/L AMNSs groups, which were 65.4% and 43.3%, respectively, above the 0 mg/L AMNSs group. The fermentation pathway revealed that AMNSs enhanced the butyrate-type metabolic pathway and the corresponding nicotinamide adenine dinucleotides (NADHand NAD⁺) ratio, and hydrogenase activity was enhanced in mesophilic fermentation. The interaction of AMNSs and MCB suggested that AMNSs could assist in electron transfer and that the released metal elements might be responsible for elevated hydrogenase activity. AMNSs also promoted the evolution of the dominant microbial community and altered the content of extracellular polymers, leading to increased production of BioH₂.

Comparison of copper and aluminum doped cobalt ferrate nanoparticles for improving biohydrogen production

Two various materials, copper and aluminum doped cobalt ferrite nanoparticles (NPs) were fabricated for investigating their effects of addition amounts on hydrogen (H₂) synthesis and process stability. CoCu_0.2Fe_1.8O₄NPs enhanced H₂ production more than CoAl_0.2Fe_1.8O₄ NPs under same condition. The highest H₂ yield of 212.25 ml/g glucose was found at optimal dosage of 300 mg/L CoCu_0.2Fe_1.8O₄ NPs, revealing the increases of 43.17% and 6.67% compared with the control without NPs and 300 mg/L CoAl_0.2Fe_1.8O₄ NPs groups, respectively. NPs level of more than 400 mg/L inhibited H₂ generation. Further investigations illustrated that CoCu_0.2Fe_1.8O₄ NPs were mainly distributed on extracellular polymer substance while CoAl_0.2Fe_1.8O₄ NPs were mostly enriched on cell membrane, which facilitated electron transfer behavior. Community structure composition demonstrated that CoCu_0.2Fe_1.8O₄ and CoAl_0.2Fe_1.8O₄ separately caused a 9.67% and 9.03% increase in Clostridium sensu stricto 1 compared with the control reactor without NPs exposure.

Integrated biohydrogen production via lignocellulosic waste: Opportunity, challenges & future prospects

Hydrogen production through biological route is the cleanest, renewable and potential way to sustainable energy generation. Productions of hydrogen via dark and photo fermentations are considered to be more sustainable and economical approach over numerous existing biological modes. Nevertheless, both the biological modes suffer from certain limitations like low yield and production rate, and because of these practical implementations are still far away. Therefore, the present review provides an assessment and feasibility of integrated biohydrogen production strategy by combining dark and photo-fermentation as an advanced biochemical processing while using lignocellulosics biomass to improve and accelerate the biohydrogen production technology in a sustainable manner. This review also evaluates practical viability of the integrated approach for biohydrogen production along with the analysis of the key factors which significantly influence to elevate this technology on commercial ground with the implementation of various environment friendly and innovative approaches.

Enhanced biohydrogen production from corn straw by basalt fiber addition

The aim of this work was to study the impact of basalt fiber (BF) on hydrogen fermentation of corn straw. The maximum of hydrogen yield and corn straw conversion rate respectively achieved 323.94 mL and 5.23% by adding 1.5 g/L BF particle with the size of 300-400 mesh, which increased by 15.74% and 15.6% respectively than control group. The BF could promote the growth of photosynthetic bacteria, subsequently influencing the products distribution and hydrogen generation. Overall, this investigation demonstrated that BF addition is an effective way to enhance biohydrogen production from corn straw.