Assessing anodic microbial populations and membrane ageing in a pilot microbial electrolysis cell M. Isabel San-Martı´n a , Ana Sotres a , Rau´ l M. Alonso a , Jordi Dı´az-Marcos b , Antonio Mor  an a , Adri  an Escapa a,c,* a Chemical and Environmental Bioprocess Engineering Group, Natural Resources Institute (IRENA), Universidad de Leon, Avda. de Portugal 41, Leon, 24009, Spain b Nanometric Techniques Unit, Scientific and Technical Centers of the University of Barcelona, Lluı´s Solei Sabarı´s 1-3, E-08028, Barcelona, Spain c Department of Electrical Engineering and Automatic Systems, Universidad de Leon, Campus de Vegazana s/n, 24071, Leon, Spain article info Article history: Received 4 December 2018 Received in revised form 11 January 2019 Accepted 28 January 2019 Available online xxx Keywords: Bioelectrochemical system Scaling-up Cation exchange membrane Waste valorization Anodic biofilm abstract First large-scale experiences of bioelectrochemical systems (BES) are underway. However, there is still little knowledge on how the different elements that integrate a BES behave in near real-life conditions. This paper aims at assessing the impact of long-term operation on the cation exchange membrane and on the anodic biofilm of two 16 L Microbial Elec- trolysis Cells (MEC) designed for hydrogen production and ammonia recovery from pig slurry. Membrane deterioration was examined by physical, chemical and microscopy techniques at different locations, revealing a strong attachment of microorganisms and a significant decay in membrane properties such as ion exchange capacity and thermal stability. Anode microbial communities did not show a dramatic shift in the eubacteria composition at different sampling areas, although the relative abundance of some bacterial groups showed a clear vertical stratification. After 100 days of continuous operation, MEC performance did not declined significantly maintaining ammonium transport rates and H 2 production rates of 15.3 gN d 1 m 2 and 0.2 LH 2 $L 1 reactor $d 1 respectively. © 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Introduction Bioelectrochemical systems (BES) represent a relatively novel technology with a wide range of potential applications, the most interesting of which (from a technoeconomical point of view) can be those that allow the production of hydrogen or other fuels by the valorization of waste streams [1]. During the past 15 years, BES have experienced an intense phase of research in many of the areas related to their development (materials, engineering and microbiology) that has paved the way for the first experiences at a pilot scale [2]. To further advance in the development of this technology, it is of utmost importance to have a clear understanding of how the different * Corresponding author.Chemical and Environmental Bioprocess Engineering Group, Natural Resources Institute (IRENA), Universidad de Le on, Avda. de Portugal 41, Leon, 24009, Spain. E-mail address: adrian.escapa@unileon.es (A. Escapa). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (xxxx) xxx https://doi.org/10.1016/j.ijhydene.2019.01.287 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: San-Martı´n MI et al., Assessing anodic microbial populations and membrane ageing in a pilot microbial electrolysis cell, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.01.287