Microbiological hydrogen (H2 ) thresholds in anaerobic continuous-flow systems: Effects of system characteristics.

Hydrogen (H2 ) concentrations that were associated with microbiological respiratory processes (RPs) such as sulfate reduction and methanogenesis were quantified in continuous-flow systems (CFSs) (e.g., bioreactors, sediments). Gibbs free energy yield (ΔÇ´ ~ 0) of the relevant RP has been proposed to control the observed H2 concentrations, but most of the reported values do not align with the proposed energetic trends. Alternatively, we postulate that system characteristics of each experimental design influence all system components including H2 concentrations. To analyze this proposal, a Monod-based mathematical model was developed and used to design a gas-liquid bioreactor for hydrogenotrophic methanogenesis with Methanobacterium bryantii M.o.H. Gas-to-liquid H2 mass transfer, microbiological H2 consumption, biomass growth, methane formation, and Gibbs free energy yields were evaluated systematically. Combining model predictions and experimental results revealed that an initially large biomass concentration created transients during which biomass consumed [H2 ]L rapidly to the thermodynamic H2 -threshold (≤1 nM) that triggerred the microorganisms to stop H2 oxidation. With no H2 oxidation, continuous gas-to-liquid H2 transfer increased [H2 ]L to a level that signaled the methanogens to resume H2 oxidation. Thus, an oscillatory H2 -concentration profile developed between the thermodynamic H2 -threshold (≤1 nM) and a low [H2 ]L (~10 nM) that relied on the rate of gas-to-liquid H2 -transfer. The transient [H2 ]L values were too low to support biomass synthesis that could balance biomass losses through endogenous oxidation and advection; thus, biomass declined continuously and disappeared. A stable [H2 ]L (1807 nM) emerged as a result of abiotic H2 -balance between gas-to-liquid H2 transfer and H2 removal via advection of liquid-phase.

Microbial H2 Consumption by a Formation Fluid from a Natural Gas Field at High-Pressure Conditions Relevant for Underground H2 Storage.

Underground hydrogen storage (UHS) has been proposed as one option for storage of excess energy from renewable sources. Depleted gas reservoirs appear suitable, but at the same time, they may be environments with potentially high microbial abundances and activities. Hydrogen (H2) is one of the most energetic substrates in such environments, and many microorganisms are able to oxidize H2, potentially leading to loss of H2 or other unwanted reactions like production of, e.g., H2S, clogging, or corrosion. This study addressed the potential of H2 consumption by naturally abundant microorganisms in formation fluid from a gas field at near in situ pressure and temperature conditions. Microbial H2 consumption was evident at ambient and 100 bar and tolerated pressure variations reflecting cycles of H2 storage. Temperature strongly influenced the activity with higher activity at 30 °C but lower activity at 60 °C. The activity was sulfate-dependent, and sulfide was produced. The microbial community composition changed during H2 consumption with an increase in sulfate-reducing prokaryotes (SRP). Thus, the presence of an SRP-containing, H2-consuming microbial community with activity at UHS-relevant pressure and temperature conditions was shown and should be taken into account when planning UHS at this and other sites.

Investigation of enhanced H2 production from municipal solid waste gasification via artificial neural network with data on tar compounds.

An artificial neural network (ANN) is a biologically inspired computational technique that imitates the behavior and learning process of the human brain. In this study, ANN technique was applied to assess the gasification of municipal solid waste (MSW) with the aim of enhancing the H2 production. The experiments were conducted using a horizontal tube reactor under different parameters: temperatures, MSW loadings, residence times, and equivalence ratios. The input and output variables (released gases) were tested and trained using back-propagation algorithm, and the data distribution by K-fold contrivance. The values of the training (80% data) and validation (20% data) dataset were found satisfactory. The values of regression coefficient (R2) for the training phase were lied between 0.9392 and 0.9991, and 0.9363 and 0.993824 for the testing phase. Whereas; the values of root mean square error (RSME) for the training phase were lied between 0.4111 and 0.8422, and between 0.1476 and 0.7320 for the testing phase. Higher H2 production of 42.1 vol% was produced at the higher reaction temperature of 900 °C with LHV of 11.2 MJ/Nm3. According to the tar analysis, the dominant compounds were aromatics (17 compounds) followed by polycyclic aromatic, phenyl, aliphatic, aromatic heterocyclic, polycyclic, and aromatic ketone compounds.

Enhancing Hydrogen Production from the Photoreforming of Lignin.

Photoreforming of lignocellulose biomass is widely recognised as a challenging but key technology for producing value-added chemicals and renewable hydrogen (H2 ). In this study, H2 production from photoreforming of organosolv lignin in a neutral aqueous solution was studied over a 0.1 wt % Pt/TiO2 (P25) catalyst with ultraviolet A (UVA) light. The H2 production from the system employing the lignin (~4.8 µmol gcat -1 h-1 ) was comparable to that using hydroxylated/methoxylated aromatic model compounds (i. e., guaiacol and phenol, 4.8-6.6 µmol gcat -1 h-1 ), being significantly lower than that from photoreforming of cellulose (~62.8 µmol gcat -1 h-1 ). Photoreforming of phenol and reaction intermediates catechol, hydroquinone and benzoquinone were studied to probe the mechanism of phenol oxidation under anaerobic photoreforming conditions with strong adsorption and electron transfer reactions lowering H2 production from the intermediates relative to that from phenol. The issues associated with catalyst poisoning and low photoreforming activity of lignins demonstrated in this paper have been mitigated by implementing a process by which the catalyst was cycled through anaerobic and aerobic conditions. This strategy enabled the periodic regeneration of the photocatalyst resulting in a threefold enhancement in H2 production from the photoreforming of lignin.

Hydrogen (H2)/Toluene (TOL) Separation via One and Two Stages of the Bis(triethoxysily)ethane (BTESE) Membranes.

The separation ability of bis(triethoxysilyl)ethane (BTESE) membranes for hydrogen (H2) purification from hydrogen (H2)/toluene (TOL) gas mixtures after a methylcyclohexane (MCH) dehydrogenation process was investigated via one-stage and two-stage membrane processes. This study revealed that BTESE membranes of varied pore sizes (0.4, 0.5, and 0.7 nm) in a one-stage configuration can manage to achieve a H2 purity ~99.9%. However, the TOL concentrations fell within a wide range, ranging from 280 to 5441 ppm. A primary goal of this research was to lower the TOL concentration in the permeate stream below 200 ppm. Hence, by applying the two-stage membrane, it was demonstrated that the TOL concentration in the permeate stream could be lowered below 200 ppm.

Mitochondria: one of the vital hubs for molecular hydrogen's biological functions.

As a novel antioxidant, a growing body of studies has documented the diverse biological effects of molecular hydrogen (H2) in a wide range of organisms, spanning animals, plants, and microorganisms. Although several possible mechanisms have been proposed, they cannot fully explain the extensive biological effects of H2. Mitochondria, known for ATP production, also play crucial roles in diverse cellular functions, including Ca2+ signaling, regulation of reactive oxygen species (ROS) generation, apoptosis, proliferation, and lipid transport, while their dysfunction is implicated in a broad spectrum of diseases, including cardiovascular disorders, neurodegenerative conditions, metabolic disorders, and cancer. This review aims to 1) summarize the experimental evidence on the impact of H2 on mitochondrial function; 2) provide an overview of the mitochondrial pathways underlying the biological effects of H2, and 3) discuss H2 metabolism in eukaryotic organisms and its relationship with mitochondria. Moreover, based on previous findings, this review proposes that H2 may regulate mitochondrial quality control through diverse pathways in response to varying degrees of mitochondrial damage. By combining the existing research evidence with an evolutionary perspective, this review emphasizes the potential hydrogenase activity in mitochondria of higher plants and animals. Finally, this review also addresses potential issues in the current mechanistic study and offers insights into future research directions, aiming to provide a reference for future studies on the mechanisms underlying the action of H2.

Therapeutic Potential of Molecular Hydrogen in Metabolic Diseases from Bench to Bedside.

Oxidative stress and chronic inflammation have been implicated in the pathophysiology of metabolic diseases, including diabetes mellitus (DM), metabolic syndrome (MS), fatty liver (FL), atherosclerosis (AS), and obesity. Molecular hydrogen (H2) has long been considered a physiologically inert gas. In the last two decades, accumulating evidence from pre-clinical and clinical studies has indicated that H2 may act as an antioxidant to exert therapeutic and preventive effects on various disorders, including metabolic diseases. However, the mechanisms underlying the action of H2 remain unclear. The purpose of this review was to (1) provide an overview of the current research on the potential effects of H2 on metabolic diseases; (2) discuss the possible mechanisms underlying these effects, including the canonical anti-oxidative, anti-inflammatory, and anti-apoptotic effects, as well as suppression of ER stress, activation of autophagy, improvement of mitochondrial function, regulation of gut microbiota, and other possible mechanisms. The potential target molecules of H2 will also be discussed. With more high-quality clinical trials and in-depth mechanism research, it is believed that H2 will eventually be applied to clinical practice in the future, to benefit more patients with metabolic disease.

The Effect of Molecular Hydrogen on Functional States of Erythrocytes in Rats with Simulated Chronic Heart Failure.

Molecular hydrogen has an anti-inflammatory and cardioprotective effect, which is associated with its antioxidant properties. Erythrocytes are subjected to oxidative stress in pathologies of the cardiovascular system, which is the cause of a violation of the gas transport function of blood and microcirculation. Therefore, our aim was to investigate the effects of H2 inhalation on the functional states of red blood cells (RBCs) in chronic heart failure (CHF) in rats. The markers of lipid peroxidation, antioxidant capacity, electrophoretic mobility of erythrocytes (EPM), aggregation, levels of adenosine triphosphate (ATP) and 2,3-diphosphoglyceric acid (2,3-DPG), hematological parameters were estimated in RBCs. An increase in EPM and a decrease in the level of aggregation were observed in groups with multiple and single H2 application. The orientation of lipoperoxidation processes in erythrocytes was combined with the dynamics of changes in oxidative processes in blood plasma, it was observed with both single and multiple exposures, although the severity of the changes was greater with multiple H2 inhalations. Probably, the antioxidant effects of molecular hydrogen mediate its metabolic action. Based on these data, we conclude the use of H2 improves microcirculation and oxygen transport function of blood and can be effective in the treatment of CHF.

Hydrogen gas alleviates lipopolysaccharide-induced acute lung injury and inflammatory response in mice.

BACKGROUND: Chronic inflammation and oxidant/antioxidant imbalance are two main pathological features associated with lipopolysaccharide (LPS)-induced acute lung injury (ALI). The following study investigated the protective role of hydrogen (H2), a gaseous molecule without known toxicity, in LPS-induced lung injury in mice and explored its potential molecular mechanisms. METHODS: Mice were randomly divided into three groups: H2 control group, LPS group, and LPS + H2 group. The mice were euthanized at the indicated time points, and the specimens were collected. The 72 h survival rates, cytokines contents, pathological changes, expression of Toll-like receptor 4 (TLR4), and oxidative stress indicators were analyzed. Moreover, under different culture conditions, RAW 264.7 mouse macrophages were used to investigate the potential molecular mechanisms of H2 in vitro. Cells were divided into the following groups: PBS group, LPS group, and LPS + H2 group. The cell viability, intracellular ROS, cytokines, and expression of TLR4 and nuclear factor kappa-B (NF-κB) were observed. RESULTS: Hydrogen inhalation increased the survival rate to 80%, reduced LPS-induced lung damage, and decreased inflammatory cytokine release in LPS mice. Besides, H2 showed remarked anti-oxidative activity to reduce the MDA and NO contents in the lung. In vitro data further indicated that H2 down-regulates the levels of ROS, NO, TNF-α, IL-6, and IL-1ß in LPS-stimulated macrophages and inhibits the expression of TLR4 and the activation of nuclear factor kappa-B (NF-κB). CONCLUSION: Hydrogen gas alleviates lipopolysaccharide-induced acute lung injury and inflammatory response most probably through the TLR4-NF-κB pathway.

Hydrogen, a Novel Therapeutic Molecule, Regulates Oxidative Stress, Inflammation, and Apoptosis.

Molecular hydrogen (H2) is a colorless and odorless gas. Studies have shown that H2 inhalation has the therapeutic effects in many animal studies and clinical trials, and its application is recommended in the novel coronavirus pneumonia treatment guidelines in China recently. H2 has a relatively small molecular mass, which helps it quickly spread and penetrate cell membranes to exert a wide range of biological effects. It may play a role in the treatment and prevention of a variety of acute and chronic inflammatory diseases, such as acute pancreatitis, sepsis, respiratory disease, ischemia reperfusion injury diseases, autoimmunity diseases, etc.. H2 is primarily administered via inhalation, drinking H2-rich water, or injection of H2 saline. It may participate in the anti-inflammatory and antioxidant activity (mitochondrial energy metabolism), immune system regulation, and cell death (apoptosis, autophagy, and pyroptosis) through annihilating excess reactive oxygen species production and modulating nuclear transcription factor. However, the underlying mechanism of H2 has not yet been fully revealed. Owing to its safety and potential efficacy, H2 has a promising potential for clinical use against many diseases. This review will demonstrate the role of H2 in antioxidative, anti-inflammatory, and antiapoptotic effects and its underlying mechanism, particularly in coronavirus disease-2019 (COVID-19), providing strategies for the medical application of H2 for various diseases.

Recent advances in studies of molecular hydrogen in the treatment of pancreatitis.

Pancreatitis is an inflammatory disease of the pancreas characterized by acinar cell injury and is associated with the abnormal release of trypsin, which results in high mortality due to systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndrome (MODS). The inflammatory response, impaired autophagic flux, endoplasmic reticulum stress (ERS) and their interactions are involved in the development of pancreatitis. Molecular hydrogen (H2) is a novel antioxidant that possesses the features of selective scavenging of oxygen free radicals and nontoxic metabolites and has been shown to be efficacious for treating infection, injury, tumors, ischemia-reperfusion organ injury, metabolic disease and several other diseases. Recent studies have found that H2 is also useful in the treatment of pancreatitis, which may be related to the mechanism of antioxidative stress, anti-inflammation, anti-apoptosis, regulation of immunity and regulation of molecular pathways. This review focuses on the pathogenesis of pancreatitis and the research progress and potential mechanisms of H2 against pancreatitis to provide theoretical bases for future research and clinical application of H2 therapy for pancreatitis.

Neuroprotective Effects of Molecular Hydrogen: A Critical Review.

Molecular hydrogen (H2) is a physiologically inert gas. However, during the last 10 years, increasing evidence has revealed its biological functions under pathological conditions. More specifically, H2 has protective effects against a variety of diseases, particularly nervous system disorders, which include ischemia/reperfusion injury, traumatic injury, subarachnoid hemorrhage, neuropathic pain, neurodegenerative diseases, cognitive dysfunction induced by surgery and anesthesia, anxiety, and depression. In addition, H2 plays protective roles mainly through anti-oxidation, anti-inflammation, anti-apoptosis, the regulation of autophagy, and preservation of mitochondrial function and the blood-brain barrier. Further, H2 is easy to use and has neuroprotective effects with no major side-effects, indicating that H2 administration is a potential therapeutic strategy in clinical settings. Here we summarize the H2 donors and their pharmacokinetics. Meanwhile, we review the effectiveness and safety of H2 in the treatment of various nervous system diseases based on preclinical and clinical studies, leading to the conclusion that H2 can be a simple and effective clinical therapy for CNS diseases such as ischemia-reperfusion brain injury, Parkinson's disease, and diseases characterized by cognitive dysfunction. The potential mechanisms involved in the neuroprotective effect of H2 are also analyzed.

Application of in-situ H2-assisted biogas upgrading in high-rate anaerobic wastewater treatment.

The H2-assisted biogas upgrading approach has recently attracted much interest as a low-cost and environmentally friendly alternative to commonly used ex-situ/ physiochemical biogas upgrading techniques. However, most studies conducted to date have been limited to anaerobic solid-waste treatment characterized by flocculant sludge and low organic loading rates (OLR). In an attempt to expand its application to high-rate anaerobic wastewater treatment, an innovative two-stage up-flow anaerobic sludge blanket reactor system was employed using anaerobic granular sludge. We found that the CH4 content of product gas was consistently >90% and that H2 and CO2 concentrations stayed below 5%, even when OLR was increased from 1 to 5 g L-1 d-1 and H2 feeding rates were increased from 0.13 to 0.63 g L-1 d-1. We were also able to show that CO (5-10%) in H2-rich syngas didn't inhibit methanogenesis or had significant impact on microbial community structure, suggesting that H2-assisted biogas upgrading with H2-rich syngas is feasible.

Inhaled Gases as Therapies for Post-Cardiac Arrest Syndrome: A Narrative Review of Recent Developments.

Despite recent advances in the management of post-cardiac arrest syndrome (PCAS), the survival rate, without neurologic sequelae after resuscitation, remains very low. Whole-body ischemia, followed by reperfusion after cardiac arrest (CA), contributes to PCAS, for which established pharmaceutical interventions are still lacking. It has been shown that a number of different processes can ultimately lead to neuronal injury and cell death in the pathology of PCAS, including vasoconstriction, protein modification, impaired mitochondrial respiration, cell death signaling, inflammation, and excessive oxidative stress. Recently, the pathophysiological effects of inhaled gases including nitric oxide (NO), molecular hydrogen (H2), and xenon (Xe) have attracted much attention. Herein, we summarize recent literature on the application of NO, H2, and Xe for treating PCAS. Recent basic and clinical research has shown that these gases have cytoprotective effects against PCAS. Nevertheless, there are likely differences in the mechanisms by which these gases modulate reperfusion injury after CA. Further preclinical and clinical studies examining the combinations of standard post-CA care and inhaled gas treatment to prevent ischemia-reperfusion injury are warranted to improve outcomes in patients who are being failed by our current therapies.

Carbon-Based Photocathode Materials for Solar Hydrogen Production.

Hydrogen is considered a promising environmentally friendly energy carrier for replacing traditional fossil fuels. In this context, photoelectrochemical cells effectively convert solar energy directly to H2 fuel by water photoelectrolysis, thereby monolitically combining the functions of both light harvesting and electrolysis. In such devices, photocathodes and photoanodes carry out the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively. Here, the focus is on photocathodes for HER, traditionally based on metal oxides, III-V group and II-VI group semiconductors, silicon, and copper-based chalcogenides as photoactive material. Recently, carbon-based materials have emerged as reliable alternatives to the aforementioned materials. A perspective on carbon-based photocathodes is provided here, critically analyzing recent research progress and outlining the major guidelines for the development of efficient and stable photocathode architectures. In particular, the functional role of charge-selective and protective layers, which enhance both the efficiency and the durability of the photocathodes, is discussed. An in-depth evaluation of the state-of-the-art fabrication of photocathodes through scalable, high-troughput, cost-effective methods is presented. The major aspects on the development of light-trapping nanostructured architectures are also addressed. Finally, the key challenges on future research directions in terms of potential performance and manufacturability of photocathodes are analyzed.

Complete dechlorination and mineralization of pentachlorophenol (PCP) in a hydrogen-based membrane biofilm reactor (MBfR).

Complete biodegradation and mineralization of pentachlorophenol (PCP), a priority pollutant in water, is challenging for water treatment. In this study, a hydrogen (H2)-based membrane biofilm reactor (MBfR) was applied to treat PCP, along with nitrate and sulfate, which often coexist in contaminated groundwater. Throughout 120-days of continuous operation, almost 100% of up to 10 mg/L PCP was removed with minimal intermediate accumulation and in parallel with complete denitrification of 20 mg-N/L nitrate. PCP initially was reductively dechlorinated to phenol, which was then mineralized to CO2 through pathways that began with aerobic activation via monooxygenation by Xanthobacter and anaerobic activation via carboxylation by Azospira and Thauera. Sulfur cycling induced by SO42- reduction affected the microbial community: The dominant bacteria became sulfate-reducers Desulfomicrobium, sulfur-oxidizers Sulfuritalea and Flavobacterium. This study provides insights and a promising technology for bioremediation of water contaminated with PCP, nitrate, and sulfate.

Hydrogen-rich water increases postharvest quality by enhancing antioxidant capacity in Hypsizygus marmoreus.

In the present study, we aimed to assess the effect of hydrogen-rich water (HRW) on the physicochemical characteristics and antioxidant capacity of Hypsizygus marmoreus during 12 days of postharvest storage at 4 °C. Different concentrations of HRW (25, 50 and 100%) were tested, and our data showed that 25% HRW treatment had the most significant effect on preservation of nutrients in H. marmoreus compared with the control group. In addition, 25% HRW treatment significantly reduced the relative electrolyte leakage rate and malonaldehyde (MDA) content (P < 0.05) and increased anti-superoxide-radical (O2-) activity compared with the control group. The activities of antioxidants, superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) were activated by 25% HRW treatment, and the expression levels of these genes were also induced. These results suggested that HRW treatment could delay rot incidence in mushrooms during storage by regulating antioxidant defense ability. This study supplies a new and simple method to maintain the quality and extend the shelf life of mushrooms.