Intensification of a microbial electrolysis cell for biohydrogen production

Abstract

Hydrogen can be the fuel of the future, and there are multiple approaches for its production and storage. Most hydrogen production comes from non-renewable sources, primarily natural gas reforming, which is efficient but unsustainable. Microbial electrolysis cells (MEC) are alternative developing technologies that exploit conductor-like properties of electrogenic bacteria to both oxidize organic contaminants and get protons reduced in a cathode, thus producing hydrogen. Here, the aim is to design a model-based optimization framework to intensify the MEC efficiency. The constructed process model is proposed by considering transport phenomena, microbial kinetics, and a secondary current distribution model to estimate steady-state reactor performance and electrical efficiency. The results show a value of 25 % for electrical efficiency as hydrogen recovered. Global sensitivity analysis was performed and determined a strong dependency on inlet liquid velocity, and a built-in, gradient-free optimization algorithm was implemented to the model to maximize electrical efficiency under a defined range of inlet liquid velocity, inlet substrate concentration, and applied voltage. The proposed model predicts a maximum increase of efficiency of about 267 % by increasing inlet velocity and substrate concentration. Intensification of the cell's performance can be greatly achieved when halving hydraulic retention time and by having a more concentrated feed.