Scaling up microbial electrolysis cells (MECs) for hydrogen production : Design, construction and operation of a 1 m3 pilot plant in an urban wastewater treatment plant

Microbial electrolysis cells (MECs) are considered a breakthrough technology in the water-energy nexus frame due to the good results obtained at lab-scale conditions: organic matter degradation with low sludge production and energy recovery as hydrogen. However, the scaling-up of these systems has found significant hurdles and the lab-scale performance has not been achieved at a higher scale. This study comprehensively details the design, construction, and operation of a 1 m MEC pilot plant integrated into an urban wastewater treatment plant (WWTP) and fed with primary effluent. The experimental trials conducted showcased the MEC performance under varying operational conditions, achieving a maximum organic matter removal efficiency of 51 % and continuous hydrogen production at a maximum rate of 8.59 L m d (0.094 m m d) with synthetic wastewater and 7.29 L m d (0.042 m m d at full capacity, 15 cassettes) with real urban primary effluent. These results are comparable to those obtained in pilot MEC at smaller scales (~100 L), demonstrating a good scalability of the proposed prototype. A techno-economic assessment was performed to evaluate the commercial potential of the pilot MEC, considering factors such as revenue from hydrogen production, electricity consumption costs and capital expenses. The outcomes of this study represent a significant advancement in the scale-up of MECs, offering valuable insights into the challenges and opportunities associated with real-world implementation. Further improvements should focus on minimizing material costs, hydrogen leakages and voltage losses to enhance scalability, as well as exploring the applicability of MECs in niches other than urban WWTP.