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Biobutanol, produced by solventogenic bacteria like Clostridium beijerinckii through acetone, butanol, and ethanol (ABE) fermentation, is a promising green alternative to fossil fuels. However, this ABE fermentation suffers drawbacks, such as a relatively low productivity that limits its industrial deployment. Electro-fermentation (EF) can modify the intracellular ratio of oxidized nicotinamide adenine dinucleotide to reduced nicotinamide (NAD+/NADH), a critical factor for butanol synthesis by C. beijerinckii, thus allowing higher product titers (or productivity) to be reached. RESULTS: The present study focuses on glucose-based ABE-EF at laboratory-scale. Three replicate EF reactors (300 mL) were constructed and used to grow C. beijerinckii. Different cathode materials were electrochemically characterized and tested. The effect of voltage application on process productivity was assessed by performing chronoamperometry tests at constant cathode potential (Ecat), ranging from −0,7 to −1,0 V vs Ag/AgCl. These trials were compared with a benchmark ABE fermentation that was performed without voltage application. Poising Ecat at −0,8 V vs Ag/AgCl resulted in the optimal EF scenario. In these conditions, the specific growth rate of bacteria was 73% higher than the benchmark ABE fermentation, with a productivity of 125,6 mg-butanol/L/h, a process yield of 0,15 g-butanol/g-glucose, and a selectivity for butanol of 87% (34%, 25%, and 11% higher than the benchmark fermentation, respectively). The addition of 0,5 mM neutral red as redox mediator in the broth led to a further improvement of butanol productivity (152,9 mg L h−1), requiring a very low energy consumption of 0,02 kWh/kg-butanol to run the EF process. CONCLUSION: Applying EF enhances the ABE fermentation in terms of butanol production, selectivity, and energy consumption.

Aquest article tracta dels sistemes bioelectroquímics (BES, bioelectrochemical systems), dels quals es descriu el funcionament, les aplicacions que tenen i els elements clau que els componen (els elèctrodes i les membranes que integren aquest tipus de reactors). A més, a partir de la recerca realitzada per LEITAT, es descriuen diverses aplicacions, processos i rendiments dels BES, com són les cel·les de combustible microbianes, els electrowetlands, les cel·les de dessalinització microbianes, els BES per a la producció de biocombustibles i els BES per a l’eliminació de contaminants o per a la recuperació de nutrients.&nbsp, This article describes the bioelectrochemical systems, including the operating principle, technology applications, key components, electrodes and membranes of the BES reactor. Additionally, on the basis of research carried out by LEITAT, a description is given of some of the applications, processes, and performances of BES systems, including the microbial fuel cell, electrowetlands, microbial desalination cells, BES systems for the production of biofuels, and BES systems for the elimination of contaminants and for the recovery of nutrients.&nbsp

Bioelectrochemical systems performing electromethanogenesis (EMG-BES) represent an emerging technology for Power-to-gas as well as wastewater treatment. Moreover, EMG-BES can be used as a high-capacity energy storage system to absorb surplus energy in the electrical grid. This paper presents a modelling approach, which is based on building an equivalent electric circuit of the EMG-BES, which can be used to emulate static and dynamic non-linear behaviour of EMG-BES for different input voltages, which is advantageous if compared to other existing models. This model is a suitable choice for future studies in the development of the electric converters for EMG-BES plants connected to the electrical grid. The proposed model consists of practical and commercial elements, including capacitors, resistors, voltage sources, and a diode. The modelling of non-linear behaviour is achieved by adding a diode to the model. Four simple tests were performed to determine the equivalent circuit parameters in a medium-scale EMG-BES prototype. This prototype was built by stacking 45 cells together and connecting them in parallel, and it was long-term operated and tested under different electric inputs to determine the model parameters. A comparative study was finally conducted as reported in this paper in order to validate the proposed model against experimental results and values collected with other models., The research leading to these results has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 712949 (TECNIOspring PLUS) and from the Agency for Business Competitiveness of the Government of Catalonia. Also, this work has been supported by the Spanish Ministry of Economy and Competitiveness under the projects RTI2018-100921-BC21. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect those of the host institutions or funders. The authors wish to acknowledge the Leitat collaborators who took part in Power2Biomethane project, which was financially supported by the Spanish Ministry of Economy and Competitiveness (RTC-2016- 5024-3, 2016)., Peer Reviewed, Postprint (author's final draft)

The development and implementation of energy storage solutions is essential for the sustainability of renewable energy penetration in the electrical system. In this regard, power-to-gas technologies are useful for seasonal, high-capacity energy storage. Bioelectrochemical systems for electromethanogenesis (EMG-BES) represent an additional power-to-gas technology to the existing chemical and biological methanation. EMG-BES process can be retrofitted in traditional anaerobic digesters, with advantages in terms of biologic process stability and high-quality biogas production. Nowadays, there are no reported studies of scaled-up EMG-BES plants for energy storage. The present work describes the setup and operation of a medium-scale EMG-BES prototype for power-to-gas, storing energy in the form of biomethane. The prototype was built by stacking 45 EMG-BES cells, accounting for a total volume of 32¿L. It was continuously fed with 10¿L¿day-1 municipal wastewater, and it was long-term operated at different voltage and temperature ranges. A steady-state current density demand of 0.5¿A¿m-2 was achieved at 32¿°C while producing 4.4¿L¿CH4¿m-2¿d-1 and removing 70% of the initial organic matter present in wastewater. Microbial competition between electro-active bacteria and acetoclastic methanogens was observed. Energy storage efficiency was estimated around 42–47%, analyzing surplus CH4 production obtained when applying voltage to the stack. A first order electric model was calculated, based on the results of a series of electrical characterization tests. The model may be used in the future to design the converter for EMG-BES plant connection to the electrical grid. The obtained results show that energy storage based on EMG-BES technology is possible, as well as its future potential, mixing renewable power overproduction, biomethane generation and wastewater treatment under the circular economy umbrella., Peer Reviewed, Postprint (author's final draft)

Peer Reviewed, Postprint (published version)

High hydrophobicity of polycyclic aromatic hydrocarbons (PAHs) is the most limiting factor for the remediation of polluted soils and aquifers. The present study analyzes the effect of three nonionic surfactants (Tween 80, BS-400, and Gold Crew) and the granulometry of soil (1%, 5%, 10%, and 20% of clay and silt) on desorption of a PAH mixture (fluorene, phenanthrene, anthracene, and pyrene). As a general trend, decrease of fine material content and increase of surfactant concentration raises desorption. However, some particularities have to be considered depending on granulometry together with the surfactant applied. Furthermore, increase of fine material content tends to reduce the importance of the PAH properties, e.g., K ow and solubility, in desorption. To complete the remediation process, biodegradation by Trametes versicolor was tested with the surfactant Tween 80. Results indicate that a high concentration of surfactant does not affect the efficiency of fungus bioremediation. Nevertheless, high fine material content in soil/aquifer can reduce the degradation rate. Moreover, desorption and biodegradation used synergically guarantee better overall results in the remediation of soils polluted by PAH mixtures than other methods that separate desorption and remediation., Peer Reviewed, Postprint (published version)

High hydrophobicity of polycyclic aromatic hydrocarbons (PAHs) is the most limiting factor for the remediation of polluted soils and aquifers. The present study analyzes the effect of three nonionic surfactants (Tween 80, BS-400, and Gold Crew) and the granulometry of soil (1 %, 5 %, 10 %, and 20 % of clay and silt) on desorption of a PAH mixture (fluorene, phenanthrene, anthracene, and pyrene). As a general trend, decrease of fine material content and increase of surfactant concentration raises desorption. However, some particularities have to be considered depending on granulometry together with the surfactant applied. Furthermore, increase of fine material content tends to reduce the importance of the PAH properties, e.g., K ow and solubility, in desorption. To complete the remediation process, biodegradation by Trametes versicolor was tested with the surfactant Tween 80. Results indicate that a high concentration of surfactant does not affect the efficiency of fungus bioremediation. Nevertheless, high fine material content in soil/aquifer can reduce the degradation rate. Moreover, desorption and biodegradation used synergically guarantee better overall results in the remediation of soils polluted by PAH mixtures than other methods that separate desorption and remediation, Peer Reviewed, Postprint (published version)