Hydrogen production from water electrolysis is one of the most promising approaches for the production of green H₂, a fundamental asset for the decarbonization of the energy cycle and industrial processes. Seawater is the most abundant water source on Earth, and it should be the feedstock for these new technologies. However, commercial electrolyzers still need ultrapure water. The debate over the advantages and disadvantages of direct sea water electrolysis when compared with the implementation of a distillation/purification process before the electrolysis stage is building in the relevant research. However, this debate will remain open for some time, essentially because there are no seawater electrolyser technologies with which to compare the modular approach. In this study, we attempted to build and validate an autonomous sea water electrolyzer able to produce high-purity green hydrogen (>90%) from seawater. We were able to solve most of the problems that natural seawater electrolyses imposes (high corrosion, impurities, etc.), with decisions based on simplicity and sustainability, and those issues that are yet to be overcome were rationally discussed in view of future electrolyzer designs. Even though the performance we achieved may still be far from industrial standards, our results demonstrate that direct seawater electrolysis with a solar-to-hydrogen efficiency of ≈7% can be achieved with common, low-cost materials and affordable fabrication methods.

This study presents an integrated approach combining microbial electrolysis cells (MECs) with three external ammonium extraction systems, Gas Diffuser (GD), Stripping Column (SP) and Thermally Assisted Stripping (SP + T), to enhance nitrogen removal and recovery from high-strength wastewater. Among the configurations, MECs operated at 0.75 V and integrated with SP + T achieved the highest performances, with current density of 8.8 A m^-2, ammonium removal and recovery rates reaching 69.8 and 37.9 gN m^-2 d^-1, Faradaic efficiency of 74.9 % and specific energy consumption for ammonium recovery of 3.3 kWh kg^-1N. The SP + T system boosted ammonia volatilization at the catholyte and accelerated ammonium transport across the cation exchange membrane, leading to improved removal and recovery performance. Concurrently, H₂ generation reached 1557.6 L H₂ m^-3 d^-1 with specific energy consumption of 31.4 kWh kg^-1 H₂. These results highlight that coupling MEC and SP + T is a promising configuration for efficient nitrogen recovery and renewable hydrogen generation, while demonstrating MECs as a sustainable technology for wastewater treatment and resource recovery. STRUCTURED The study presents a novel approach for enhancing nitrogen recovery from wastewater using MECs integrated with different ammonium stripping systems. By evaluating three configurations, gas diffuser (GD), ambient-temperature stripping (SP) and thermally assisted MEC stripping system (SP + T), this work systematically investigates how operational strategies affect the performance of nitrogen removal and recovery. Key performance indicators such as current density, Faradaic efficiency, specific energy consumption and hydrogen production are quantified and compared as well. Furthermore, organic removal rates, percentage and energy efficiency of organic matter treatment in the anode are also assessed. The findings described highlight the importance of optimizing operational parameters such as temperature and contact surface to maximize ammonium recovery in MECs. The SP + T approach is relevant for bioelectrochemical and wastewater treatment systems aiming to optimize nitrogen management and valorization. Furthermore, the study includes a comprehensive energy analysis and contextualizes the results with respect to conventional ammonia production technologies such as the Haber-Bosch process, among others. Thus, these results are of relevance to the fields of wastewater treatment, nutrient recovery, energy/hydrogen production, environmental biotechnology and circular economy, offering a scalable and energy-efficient solution for nutrient valorization.

Industrial activity has resulted in heavy metals anthropogenic contamination of groundwater, especially in industrial or mining areas. Bioelectrochemical systems (BES) can be used for metals removal and recovery from aqueous solutions. In the framework of GREENER project, double-chamber BES have been adopted to treat groundwater from industrial sites containing copper, nickel and zinc (Cu, Ni and Zn), among other contaminants. Two operation modes, (i) short-circuited microbial fuel cell (MFC), and (ii) power supply driven microbial electrolysis cell (MEC, poisoning the cathode at -0.4 V vs. Ag/AgCl), were studied for metals removal at lab-scale. Two control reactors were run to evaluate metals adsorption on cathodes and membranes, and the effect of anolyte composition. Synthetic water containing different concentrations of Cu, Ni and Zn were treated, and metals removal pathways were studied. MEC and MFC performed similarly and the highest removal efficiencies were 97.1±3.6%, 50.7±6% and 74,5% for Cu, Ni and Zn respectively, from initial concentrations in the range of 1.1-1.5 mM.

Conventional polluted groundwater remediation struggles with persistent metal(loid)s, creating a need for integrated bioelectrochemical systems (BESs) and phytoremediation. The proposed configuration consisted of two sequential BESs, a microbial fuel cell (MFC) followed by a microbial electrolysis cell (MEC), whose treated effluent and exhausted anolyte were subsequently polished in individual subsurface vertical-flow macrophyte mesocosms (VFMMs), planted either with Phragmites australis, Scirpus holoschoenus, or Typha angustifolia. The overall treatment period was 38 days, comprising 8 days of BES treatment followed by 30 days of VFMM treatment. With MFC-MEC pretreatment, an overall 91% metal(loid) removal efficiency (RE) was noted, with REs of >99% for Fe and Cu, and between 71% and 92% for Al, Ni, Zn, Cd, and As, significantly increasing groundwater pH from 2.66 to 4.65, at p < 0.05. Macrophyte mesocosms, notably with P. australis and S. holoschoenus, further reduced residual Cu, Cd, Zn, and As levels below Flemish groundwater sanitation standards, nutrient concentrations and ecotoxicity (as demonstrated by Aliivibrio fischeri bioluminescence assays). Residual Ni was reduced by >99.9% but remained above regulatory thresholds. BES–phytoremediation sequential integration proved to be an effective biotreatment that combines the rapid contaminant removal capacity of BES with the polishing and ecological stabilization functions of constructed wetlands.