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Editorial ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Energy Res. | doi: 10.3389/fenrg.2019.00113

Editorial: Microbial Fuel Cells: from Fundamentals to Applications

  • 1Faculty of Engineering, University of Porto, Portugal

Wastewaters streams that contain heavy metals require further treatment as they are typically non-biodegradable pollutants with a toxic effect to the environment and human health. Moreover, there is an economic interest on its recovery since they are non-renewable and expensive raw materials. Therefore, the metal recovery is a very interesting application for BES, since most of the commonly used methods to perform this recovery (chemical, physical or biological) require an energy input and sludge disposal. Ezziat et al. (2019) provided a review regarding the metals removal/recovery from different effluents using a MFC, where its main principles and fundamentals are summarize. The different studies on metal removal/recovery in single chamber (SCMFCs) and double chamber MFCs (DCMFCs), as well as the major challenges that this technology needs to face before its application, such as its thermodynamic limits, heavy metals biotoxicity, pH imbalance, and membrane biofouling, are also presented.Taking aside the promising prospects of the BES, their reduced power outputs, since their performance rely on different phenomena and processes, such as the microorganisms activity, the biofilm formation, the electron transfer mechanism, the interaction between the biofilm and the electrode and the electrochemical reactions, and their high costs remain challenging. Moreover, until now it was not reached any consent regarding the best design as well as the best electrodes and separator materials to scale-up this technology.Towards an improvement of the power output and lowering the costs of the scaled-up systems, Gajda et al. (2018) developed a MFC stack using a cost effective ceramic as a membrane/chassis for the reactor architecture, by compacting the design and exploring the ceramic support as the building block for small-scale modular multi-unit systems.The results showed that the power output of the small reactors outperform the large ones due to an increase of the surface area-volume ratio of the ceramic membrane, a more efficient mass transport and a decrease of the electrodes distance. It was, also, found that the power output was influenced by the type and thickness of the ceramic separator as well as the anode electrode surface area. Higher areas improved the power output of the individual units increasing the overall system power output. The MFC stack composed by 560 small-scale units showed a power output up to 245 mW. As electrochemically active biofilms are critical to the function of BES, Cotterill et al. (2018) studied the formation and composition of anodic biofilms on two pilot-scale MECs operated for over 6 months in continuous mode with a domestic wastewater and inoculated with that same wastewater. The major goals of this work were the identification of the bacterial community, through Illumina 16S rDNA sequencing, determine, by NCM (neutral community model), the dominant processes behind the community assembly and compare the spatial variation of the community composition and the biofilm distribution within and across the anode surface with increased scaleup. The results from these approaches were used to provide suggestions to the design, start-up and operating conditions towards the optimization of the biofilm in pilot-scale MEC. It was found that the community composition was mainly governed by stochastic processes, that the technology can be used on most of the domestic wastewaters, as long as the anodes are seeded with the target wastewater, and that the deterministic factors, such as the applied voltage and flow rate, may also play a role in establishing the anodic community.bioelectrochemical system with an anaerobic membrane bioreactor (AnMBR) to produce electricity, reducing the overall energy consumption of wastewater treatment.Therefore, a microbial anode was integrated into an AnMBR, under two different configurations, and this system was used for the treatment of a synthetic brewery wastewater. As fouling is a drawback in AnMBRs, the authors investigated the effect of two fouling mitigation methods on the permeate fluxes and current densities. The results revealed that permeate fluxes were influenced by the membrane pore size and that the cathode position do not influence the permeate fluxes and current densities, but have a clearly influence on the permeate pH. Using a turbulence promotor increased the permeate fluxes and the current densities in filtering anode and that the hybrid anode resulted in similar current densities, but higher permeate fluxes than the filtering one. The hybrid anode configuration is a very promising design since combines high permeate fluxes on conventional non-conductive filters with current generation on an inexpensive conductive material.In summary, this research topic intends to make the difference among the few similar titles available on the bioelectrochemical systems field, since discusses the key work done in order to improve its performance based on its limitations, regarding both fundamental and technological issues.The use of fossil fuels to produce energy leads to two major problems: fossil fuels are limited in amount and its use lead to different environmental problems. Therefore, new technologies, more environmental friendly ones, are needed to progressively replace fossil sources. Bioelectrochemical systems (BES) are considered as a new promising technology, since they can generate electricity from the wastes produced by human beings, which contain substrates and microorganisms. Moreover, when a wastewater is used, they can perform waste treatment while recovering energy, offsetting the operational costs of wastewater treatment plants. However, their lower power outputs and higher costs remain problematic, presenting the main challenges towards their use.Therefore, for a successful implementation of these systems, their benefits (hydrogen and chemicals of high value production, wastewater treatment and metal and nutrient removal/recovery) should be higher than their costs (implementation and operation/maintenance).This research topic provide an overview on the challenges and developments in BES, namely on microbial fuel cells (MFCs) and microbial electrolysis cells (MECs), towards its optimization and massive application. This research topic has as main goal to be a valuable reference for BES and energy researchers, designers and manufacturers.

Keywords: bioenergy, Bioelectrochemial systems, challanges, Scale - up, applications, Microbial fuel cell, Microbial electrolysis cell, configuration

Received: 19 Sep 2019; Accepted: 30 Sep 2019.

Copyright: © 2019 Oliveira and Pinto. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Dr. V B. Oliveira, Faculty of Engineering, University of Porto, Porto, Portugal, vaniaso@fe.up.pt
Dr. A M. Pinto, Faculty of Engineering, University of Porto, Porto, Portugal, apinto@fe.up.pt