Production & Supply Chain

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.

Water electrolyzers play a crucial role in green hydrogen production. However their efficiency and scalability are often compromised by bubble dynamics across various scales from nanoscale to macroscale components. This review explores multi-scale modeling as a tool to visualize multi-phase flow and improve mass transport in water electrolyzers. At the nanoscale molecular dynamics (MD) simulations reveal how electrode surface features and wettability influence nanobubble nucleation and stability. Moving to the mesoscale models such as volume of fluid (VOF) and lattice Boltzmann method (LBM) shed light on bubble transport in porous transport layers (PTLs). These insights inform innovative designs including gradient porosity and hydrophilic-hydrophobic patterning aimed at minimizing gas saturation. At the macroscale VOF simulations elucidate two-phase flow regimes within channels showing how flow field geometry and wettability affect bubble discharging. Moreover artificial intelligence (AI)-driven surrogate models expedite the optimization process allowing for rapid exploration of structural parameters in channel-rib flow fields and porous flow field designs. By integrating these approaches we can bridge theoretical insights with experimental validation ultimately enhancing water electrolyzer performance reducing costs and advancing affordable highefficiency hydrogen production.

The paper investigates the potential of co-electrolysis as a viable pathway for hydrogen production and industrial decarbonization expanding on previous studies on water electrolysis. The analysis adopts a general and critical perspective aiming to assess the realistic scope of this technology with regard to current energy and environmental needs. Although co-electrolysis theoretically offers improved efficiency by simultaneously converting H2O and CO2 into syngas the practical advantages are difficult to consolidate. The study highlights that the energetic margins of the process remain relatively narrow and that several key aspects including system irreversibility and the limited availability of CO2 in many contexts significantly constrain its applicability. Despite the growing interest and promising technological developments co-electrolysis still faces substantial challenges before it can be implemented on a larger scale. The findings suggest that its success will depend on targeted integration strategies advanced thermal management and favorable boundary conditions rather than on the intrinsic efficiency of the process alone. However there are specific sectors where assessing the implementation potential of co-electrolysis could be of interest a perspective this paper aims to explore.

The current study evaluates the feasibility of a forward osmosis membrane bioreactor (FO-MBR) for dark fermentation aiming at simultaneous biohydrogen production and wastewater treatment. Optimal microbial inoculation was achieved via heat-treated activated sludge enriching Clostridium sensu stricto 1 and yielding up to 2.21 mol H2.(mol hexose)− 1 in batch mode. In continuous operation a substrate concentration of 4.4 g L− 1 and a hydraulic retention time (HRT) of 12 h delivered the best results producing 1.51 mol H2.(mol hexosesupplied) − 1 . The FO-MBR configured with a 1.1 m2 hollow fiber side-stream membrane module and operated under dynamic HRT (2.5–12 h) dependent on membrane flux was integrated with intermittent CSTR (Continuous stirred tank reactor) operation to counter metabolite accumulation. This system outperformed a conventional CSTR achieving a hydrogen yield of 1.78 mol H2.(mol hexosesupplied) − 1 . Remarkable treatment efficiencies were observed with BOD5 COD and TOC removal rates of 95.32 % 99.02 % and 99.10 % respectively and an 83.8 % reduction in total waste volume. Additionally the FO-MBR demonstrated strong antifouling performance with 96.14 % water flux recovery achieved after a brief 5 min hydraulic rinse following 47.5 h of continuous highstrength broth exposure. These results highlight the FO-MBR system’s ability as a sustainable and highperformance alternative for integrated hydrogen production and effluent treatment. Further studies are recommended to address long-term fouling control and metabolite management for industrial scalability.

Photoelectrochemical (PEC) water splitting is a promising technology for green hydrogen production by harnessing solar energy. Traditionally this sustainable approach is studied under light intensity of 100 mW/cm2 mimicking the natural solar irradiation at the Earth’s surface. Sunlight can be easily concentrated using simple optical systems like Fresnel lens to enhance charge carrier generation and hydrogen production in PEC water splitting. Despite the great potentials this strategy has not been extensively studied and faces challenges related to the stability of photoelectrodes. To prompt the investigations and applications this work outlines the best practices and protocols for conducting PEC solar water splitting under concentrated sunlight illumination incorporating our recent advancements and providing some experimental guidelines. The key factors such as light source calibration photoelectrode preparation PEC cell configuration and long-term stability test are discussed to ensure reproducible and high performance. Additionally the challenges of the expected photothermal effect and the heat energy utilization strategy are discussed.

This study focuses on enhancing the efficiency of alkaline water electrolysis technology a key process in green hydrogen production by leveraging the synergy of magnetic fields and in situ electrode activation. Optimizing AWE efficiency is essential to meet increasing demands for sustainable energy solutions. In this research nickel mesh electrodes were modified through the application of magnetic fields and the addition of hypo-hyper d-metal (cobalt complexes and molybdenum salt) to the electrolyte. These enhancements improve mass transfer facilitate bubble detachment and create a high-surface-area catalytic layer on the electrodes all of which lead to improved hydrogen evolution rates. The integration of magnetic fields and in situ activation achieved over 35% energy savings offering a cost-effective and scalable pathway for industrial green hydrogen production.

This review investigates hydrogen production via photocatalysis using ammonia a carbon-free source potentially present in wastewater. Photocatalysis offers low energy requirements and high conversion efficiency compared to electrocatalysis thermocatalysis and plasma catalysis. However challenges such as complex material synthesis low stability spectral inefficiency high costs and integration barriers hinder industrial scalability. The review addresses thermodynamic requirements reaction mechanisms and the role of pH in optimizing photocatalysis. By leveraging ammonia’s potential and advancing photocatalyst development this study provides a framework for scalable sustainable hydrogen production and simultaneous ammonia decomposition paving the way for innovative energy solutions and wastewater management.

This study offers a novel techno-economic evaluation of a small hydrogen generation system included into a residential villa in Sharjah. The system is designed to utilize solar energy for hydrogen production using an electrolyzer. The study assesses two scenarios: one lacking a fuel cell and the other incorporating a fuel cell stack for backup power. The initial scenario employs a solar-powered electrolyzer for hydrogen production attaining a competitive levelized cost of energy (LCOE) of $0.1846 per kWh and a hydrogen cost of $4.65 per kg. These data underscore the economic viability of utilizing electrolyzers for hydrogen generation. The system produces around 1230 kg of hydrogen per annum rendering it appropriate for many uses. Nevertheless the original investment expenditure of $73980 necessitates more optimization. The second scenario includes a 10 kW fuel cell for energy autonomy. This scenario has a marginally reduced LCOE of 0.1811 $/kWh and a cumulative net present cost of $72600. The fuel cell runs largely at night proving the efficiency of the downsizing option in decreasing capital expense. The system generates electricity from solar panels (66.1 MWh/year) and the fuel cell (16.9 MWh/year) exhibiting a multi-source power generating technique. The results indicate that scaled-down hydrogen generation systems both with and without fuel cells may offer sustainable and possibly lucrative renewable energy options for household use especially in areas with ample solar resources such as Sharjah.

Green hydrogen (GH2) a sustainable and clean energy carrier is increasingly regarded as a solution to energy challenges and environmental issues. Industrial wastewater possesses a significant potential for hydrogen generation using biological chemical and electrochemical methods. This review analysis evaluates progress in GH2 production from industrial wastewater highlighting its environmental and cost benefits. Process optimization technological improvements and enhancements in catalysts for chemical and electrochemical hydrogen generation are also provided. It also considers the integration of GH2 production methods with wastewater treatment procedures to achieve synergistic benefits including enhanced pollutant removal and energy recovery. Challenges associated with GH2 production include substrate variability economic viability reactor scalability and environmental sustainability are also discussed. Also this review provides a future outlook to promote sustainable energy solutions and tackle global environmental issues related to GH2 from industrial wastewater.

This study investigates the integration of multiple energy carriers within a unified multi-carrier energy system using an energy cascade approach. The system harnesses geothermal energy to power interconnected subsystems including an organic Rankine cycle (ORC) liquefied natural gas (LNG) and a solid oxide fuel cell (SOFC) stack. The dual ORC system and LNG stream are directly fed from the geothermal source while the SOFC stack uses methane produced during LNG regasification. Besides electricity the system generates hydrogen and desalinated water by incorporating a proton exchange membrane (PEM) electrolyzer and a reverse osmosis (RO) desalination plant. The electricity produced by the upper ORC powers the PEME for hydrogen production while freshwater production is supported by the combined output from the lower ORC LNG turbine and SOFC. A detailed thermo-economic analysis assesses the system’s efficiency and economic feasibility. Optimization efforts focus on three areas: electrical efficiency hydrogen and freshwater production using artificial neural networks (ANN) and genetic algorithms (GA). The optimization results reveal that Ammonia-propylene excels in electrical efficiency R1234ze(Z)-ethylene in net power output R1233zd(E)-propylene in cost-effectiveness R1234ze(Z)-propylene in hydrogen production and Ammonia-ethane in water production. The study offers valuable insights into enhancing the efficiency cost-effectiveness and sustainability of integrated energy systems.