Increased performance of hydrogen production in microbial electrolysis cells under alkaline conditions Laura Rago, Juan A. Baeza ⁎, Albert Guisasola GENOCOV, Departament d'Enginyeria Química, Biològica i Ambiental, Escola d'Enginyeria, Universitat Autònoma de Barcelona, 08193 Bellaterra (Barcelona), Spain abstract article info Article history: Received 4 November 2015 Received in revised form 27 December 2015 Accepted 24 January 2016 Available online 27 January 2016 This work reports the first successful enrichment and operation of alkaline bioelectrochemical systems (microbial fuel cells, MFC, and microbial electrolysis cells, MEC). Alkaline (pH = 9.3) bioelectrochemical hydrogen pro- duction presented better performance (+117%) compared to conventional neutral conditions (2.6 vs 1.2 litres of hydrogen gas per litre of reactor per day, L H2 ·L -1 REACTOR ·d -1 ). Pyrosequencing results of the anodic bio- film showed that while Geobacter was mainly detected under conventional neutral conditions, Geoalkalibacter sp. was highly detected in the alkaline MFC (21%) and MEC (48%). This is the first report of a high enrichment of Geoalkalibacter from an anaerobic mixed culture using alkaline conditions in an MEC. Moreover, Alkalibacter sp. was highly present in the anodic biofilm of the alkaline MFC (37%), which would indicate its potentiality as a new exoelectrogen. © 2016 Elsevier B.V. All rights reserved. Keywords: Alkalibacter Alkaline Geoalkalibacter Microbial electrolysis cell (MEC) Microbial fuel cell (MFC) Pyrosequencing 1. Introduction Bioelectrochemical systems represent a promising strategy to har- vest energy and to obtain added value products from renewable sources with high organic content (e.g. wastewaters). Bioelectrochemistry com- bines electrochemistry with the metabolism of anode respiring bacteria (ARB), also known as exoelectrogenic bacteria. These bacteria are able to transfer the electrons obtained in their metabolism to an external solid anode which is, thus, the final electron acceptor. These electrons flow through an electrical circuit to a cathode where a reductive reaction takes place [1]. In a microbial fuel cell (MFC), oxygen reduction occurs on the cathode and the overall process is spontaneous, leading to electricity generation simultaneous to substrate oxidation. On the other hand, added-value compounds (such as hydrogen) are produced in the cath- ode of a microbial electrolysis cell (MEC) through a reduction reaction. These processes are not, in general, thermodynamically spontaneous and additional energy supply is required [2,3]. Geobacteraceae and Shewanaellaceae families are the most studied genera of ARB [4], with Geobacter being the commonly found genus in acetate-fed high bioelectrochemical systems [5–8]. Most of current studies are based on moderate pH conditions. How- ever, bioelectrochemical systems should extend their applicability range to include wastewater treatment and energy generation under different pH scenarios. Alkaline exoelectrogenesis is, a priori, very stim- ulating since: i) the highest current densities ever achieved by pure cul- tures were found under alkaline conditions with the Geoalkalibacter genus [9]; ii) Geoalkalibacter are, in turn, very attractive since they are also halophilic and give successful results under high-salt conditions [9–12]; iii) alkaliphilic environments may also be favorable to prevent acidity buildup [13,14]; iv) an alkaline environment could create a more selective and favorable environment for ARB when competing with methanogens for the electron donor and v) alkaline bioelectrochemical systems can be a suitable technology for the direct treatment of alkaline wastes (e.g. beamhouse wastewaters from leather tannery or wastewaters with glycerol produced in alkaline biodiesel production). Thus, the aim of this study is the first experimental evaluation of the long-term performance of mixed-culture bioelectrochemical systems under alkaline conditions. Electrochemical and advanced microbiologi- cal tools are used to gain insight into the process performance. 2. Materials and methods 2.1. Reactor description, inoculation and operation An air-cathode MFC, designed and built as previously described [15], was used for enrichment of exoelectrogenic bacteria under alkaline con- ditions (inoculum microbial fuel cell, i-MFC). It consisted of a 400 mL glass vessel with a lateral aperture for the cathode assembling, which was a graphite fiber cloth that had a PTFE diffusion layer and a catalytic Bioelectrochemistry 109 (2016) 57–62 ⁎ Corresponding author. E-mail addresses: Laura.Rago@live.com (L. Rago), JuanAntonio.Baeza@uab.cat (J.A. Baeza), Albert.Guisasola@uab.cat (A. Guisasola). http://dx.doi.org/10.1016/j.bioelechem.2016.01.003 1567-5394/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Bioelectrochemistry journal homepage: www.elsevier.com/locate/bioelechem