Hydrogen is  a clean energy source and an important candidate to replace fossil fuels in the near future (energy transition). However, traditional hydrogen production is achieved through processes that are expensive and non-sustainable require high amounts of energy, such as carbon gasification or steam methane reforming. Waste waters are considered a cheap and abundant energy source, as they contain high amounts of organic compounds. Therefore, the hydrogen production from waste water can be a useful solution in order to reduce the energy costs associated with traditional processes. 

REGENERA project (CDTI- Misiones 2019) investigates the delocalized storage of energy from renewable energies in the form of green fuels, hydrogen and methane. This communication presents the BES-BioH₂ laboratory concept, a “Power-to-Gas” technology that aims to generate hydrogen (H₂) by using a microbial electrochemical cell. The objective is to achieve an integrated system at laboratory scale which allows the simultaneous waste water treatment, hydrogen production and biogas upgrading (achieving a purity >95% of CH₄). 

Bioelectrochemical systems (BES) combine electrochemistry with the metabolism of electroactive microorganisms for energy production. In Microbial Electrolysis Cells (MECs), electroactive bacteria grow building a biofilm on the surface of a conductive anode, which acts as electron acceptor. The electroactive microorganisms oxidize organic matter to CO₂ under anaerobic conditions and the electrons obtained in the process are transferred from the anode to the cathode through an electrical circuit [1]. The cathodic reaction is the H₂ formation through H₂O reduction under alkaline conditions. The reduction of water to hydrogen is a non-spontaneous process, so the application of an external potential is required.

This study presents the experimental results using different real waste waters (urban and industrial) and discusses on the potential of various organic substrates for hydrogen production. Thus, the energy cost for hydrogen production (kWh/kg H₂), the chemical organic demand removal rate (g/m³ day) and the hydrogen production rate (m³ hydrogen/m³ reactor) are presented in order to compare the present system with conventional system for urban waste water treatment. Finally, the study suggests main limitations and opportunities for the implementation at real scale, as the final objective of REGENERA project is the development of a prototype of 500 L capacity by the end of year 2024, with capacity to produce 1-10 Nm³H₂/day.