Impact of the start-up process on the microbial communities in biocathodes for electrosynthesis

[EN]This study elucidates the impact of the start-up strategies on the microbial communities that evolve on the biofilm of a biocathode. Using reductive start-up potentials and a highly diverse inoculum, this start-up failed to produce any biofilm. When a less species richness inoculum from an anaerobic environment was used with the same reductive initial potential, a specialised biofilm was formed and a highly productive biocathode was developed in terms of acetic acid and also current production. However, using oxidative start-up potential led to rapid electroactive biofilm development, although the final composition of the biofilm was highly dependent on the inoculum used. So, using the diverse RM inoculum, a final specialised biofilm grew on the electrode, also giving high acetate and current generation. However, when using the less species richness AD inoculum, it was found that a nonspecialised biofilm was developed and lower acetic acid production was found. Importantly, a higher specialisation of the biofilm leads to an improvement in acetate generation, probably due to lowered influence of undesirable secondary methabolic pathways. Moreover, it has been shown that the coupling of H2 producing bacteria and acetic acid bacteria play an important role in acetate productionSIThis research was possible thanks to the financial support of the ‘Ministerio de Economía y Competitividad’ project ref: CTQ2015-68925-R, cofinanced by FEDER funds. Raúl Mateos thanks the Spanish ‘Ministerio de Educación, Cultura y Deporte’ for the FPU Grant (FPU14/01573). Ana Sotres thanks the regional ‘Junta de Castilla y León’ for the postdoctoral contract associated with project ref: LE060U16

Integrating microbial electrochemical technologies with anaerobic digestion to accelerate propionate degradation

[EN] The aim of this study is to evaluate the integration of microbial electrochemical technologies (MET) with anaerobic digestion (AD) to overcome AD limitations caused by propionate accumulation. The study focuses on understanding to what extent the inoculum impacts on the behaviour of the integrated systems (AD-MET) from the perspective of propionate degradation, methane production and microbial population dynamics. Three different inocula were used: two from environmental sources (anaerobic sludge and river sediment) and another one from a pre-enriched electroactive consortium adapted to propionate degradation. Contrary to expectations, the reactor inoculated with the pre-enriched consortium was not able to maintain its initial good performance in the long run, and the bioelectrochemical activity collapsed after three months of operation. On the other hand, the reactor inoculated with anaerobic sludge, although it required a relatively longer time to produce any observable current, was able to maintain an electrogenic activity operation (0.8 A m−2), whilst showcasing the positive contribution of AD-MET integration into tackling propionate accumulation and enhancing methane yield (338 mL gCOD−1). However, it must also be highlighted that from a purely energetic point of view the AD-MET was not favourable.SIMinisterio de Economía y CompetitividadJunta de Castilla y LeónEnte Regional de la Energía de Castilla y Leo

Bioelectrochemical Systems for Energy Valorization of Waste Streams

Bioelectrochemical systems (BES) encompass a group of technologies derived from conventional electrochemical systems in which the electrodic reactions are directly or indirectly linked to the metabolic activity of certain types of microorganisms. Although BES have not yet made the leap to the commercial scale, these technologies hold a great potential, as they allow to valorize different liquid and gas waste streams. This chapter is devoted to exploring some of the possibilities that BES offer in the management and valorization of wastes. More specifically, it focuses on analyzing practical aspects of using BES for energy valorization of wastewaters and CO2-rich streams. Here, it is shown how BES can compete, in terms of energy usage, with conventional wastewater treatment technologies by exploiting the energy content of some of the chemicals present in the wastewater. Moreover, it explores how BES could enable using wastewater treatment plants as load regulation system for electrical grids. It also includes some insights on the capability of BES to recover valuable products such as fertilizers form wastes, a feature that allows this technology to promote energy efficiency in the fertilizers industry, and a sector that demands substantial amounts of energy in our world today. Finally, some of the most relevant scale-up experiences in the field are also covered

Comparison of Activation Methods for 3D-Printed Electrodes for Microbial Electrochemical Technologies

Supplementary Materials: The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/app12010275/s1, Figure S1. Current density profiles of two successive cycles at the end of a 60 days period that allowed for the development of a stable biofilm; Table S1: Fitted parameters to EC 1 (DMF and acetone electrodes); Table S2: Fitted parameters to EC 2 (control and electrochemical-treated electrodes); Figure S2. Equivalent circuits for abiotic electrode essays’ modellization.1) DMF and acetone 2) Control and electrochemical treatment.[EN] Three-dimensional printing could provide flexibility in the design of a new generation of electrodes to be used in microbial electrochemical technologies (MET). In this work, we demonstrate the feasibility of using polylactic acid (PLA)/graphene—a common 3D-printing material—to build custom bioelectrodes. We also show that a suitable activation procedure is crucial to achieve an acceptable electrochemical performance (plain PLA/graphene bioanodes produce negligible amounts of current). Activation with acetone and dimethylformamide resulted in current densities similar to those typically observed in bioanodes built with more conventional materials (about 5 Am−2). In addition, the electrodes thus activated favored the proliferation of electroactive bacteria.SIMinisterio de Economía y CompetitividadEnte Regional de la Energía de Castilla y LeonThis research was funded by “Ministerio de Economía y Competitividad (Gobierno de España) grant number: PID2020-115948RB-I00 (MINECO/FEDER, EU) and “Ente Regional de la Energía de Castilla y Leon”, grant number: EREN_2019_L3_ULE

Assessing anodic microbial populations and membrane ageing in a pilot microbial electrolysis cell

Bioelectrochemical system[EN] 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 Electrolysis 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 H2 production rates of 15.3 gN d−1 m−2 and 0.2 LH2·L−1reactor·d−1 respectively.SIMinisterio de Economía y CompetitividadJunta de Castilla y LeónMinisterio de Educación, Cultura y Deport

Simulating the detection of dioxin-like pollutants with 2D surface-enhanced Raman spectroscopy using h-BNC substrates

The ability of 2D hybrid structures formed by boron, nitrogen and carbon atoms (h-BNCs) to act as potential substrates for the surface-enhanced Raman spectroscopy (SERS) detection of dioxin-like pollutants is theoretically analyzed. The strong confinement and high tunability of the electromagnetic response of the carbon nanostructures embedded within the h-BNC sheets point out that these hybrid structures could be promising for applications in optical spectroscopies, such as SERS. In this work, two model dioxin-like pollutants, TCDD and TCDF, and a model h-BNC surface composed of a carbon nanodisk of ninety-six atoms surrounded by a string of borazine rings, BNC96, are used to simulate the adsorption complexes and the static and pre-resonance Raman spectra of the adsorbed molecules. A high affinity of BNC96 for these pollutants is reflected by the large interaction energies obtained for the most stable stacking complexes, with dispersion being the most important contribution to their stability. The strong vibrational coupling of some active modes of TCDF and, specially, of TCDD causes the static Raman spectra to show a ”pure” chemical enhancement of one order of magnitude. On the other hand, due to the strong electromagnetic response of BNC96, confined within the carbon nanodisk, the pre-resonance Raman spectra obtained for TCDD and TCDF display large enhancement factors of 108 and 107, respectively. Promisingly, laser excitation wavelengths commonly used in SERS experiments also induce significant Raman enhancements of around 104 for the TCDD and TCDF signals. Both the strong confinement of the electromagnetic response within the carbon domains and the high modulation of the resonance wavelengths in the visible and/or UV region in h-BNCs should lead to a higher sensitivity than that of graphene and white graphene parent structures, thus overcoming one of the main disadvantages of using 2D substrates for SERS applications.Xunta de Galicia | Ref. GRC2019/2

Degradation of 2-mercaptobenzothizaole in microbial electrolysis cells: Intermediates, toxicity, and microbial communities

[EN] The compound 2-mercaptobenzothizaole (MBT) has been frequently detected in wastewater and surface water and is a potential threat to both aquatic organisms and human health (its mutagenic potential has been demonstrated). This study investigated the degradation routes of MBT in the anode of a microbial electrolysis cell (MEC) and the involved microbial communities. The results indicated that graphene-modified anodes promoted the presence of more enriched, developed, and specific communities compared to bare anodes. Moreover, consecutive additions of the OH substituent to the benzene ring of MBT were only detected in the reactor equipped with the graphene-treated electrode. Both phenomena, together with the application of an external voltage, may be related to the larger reduction of biotoxicity observed in the MEC equipped with graphene-modified anodes (46.2 eqtox∙m−3 to 27.9 eqtox∙m−3).SIThis research was possible thanks to the financial support by ‘Consejería de Educación de la Junta de Castilla y León’ (ref: LE320P18), a project co-financed by FEDER funds. R. M. Alonso thanks the University of León for the predoctoral contract. M. Canle acknowledges financial support from the Ministerio de Economía y Competitividad (Spain) through project CTQ2015-71238-R (MINECO/FEDER), and regional government Xunta de Galicia (project GPC ED431B 2017/59), respectively

Characterization of Anaerobic Biofilms Growing on Carbon Felt Bioanodes Exposed to Air

Supplementary Materials: The following are available online at https://www.mdpi.com/2073-4344/10/11/1341/s1, Figure S1: Dissolved oxygen profile. Rejected because the data acquisition system was accidentally interrupted at the end of the experiment; Figure S2: Another dissolved oxygen profile. Rejected because the data acquisition system was accidentally interrupted at the end of the experiment.[EN] The role of oxygen in anodic biofilms is still a matter of debate. In this study, we tried to elucidate the structure and performance of an electrogenic biofilm that develops on air-exposed, carbon felt electrodes, commonly used in bioelectrochemical systems. By simultaneously recording the current density produced by the bioanode and dissolved oxygen concentration, both inside and in the vicinity of the biofilm, it was possible to demonstrate the influence of a protective aerobic layer present in the biofilm (mainly formed by Pseudomonas genus bacteria) that prevents electrogenic bacteria (such as Geobacter sp.) from hazardous exposure to oxygen during its normal operation. Once this protective barrier was deactivated for a long period of time, the catalytic capacity of the biofilm was severely affected. In addition, our results highlighted the importance of the material’s porous structure for oxygen penetration in the electrode.SIJunta de Castilla y LeonThis research was possible thanks to the financial support by ‘Consejería de Educación de la Junta de Castilla y León’ (ref: LE320P18), a project co-financed by FEDER funds. R. M. Alonso thanks the University of León for his predoctoral contract

Complete arsenic removal from water using biocatalytic systems based on anaerobic films grown on carbon fibers

[EN] Arsenic is a hazardous metalloid with potentially negative impacts on both the environment and human health. Current methods of arsenic remediation are expensive and can cause secondary contamination. In this paper we explore the potential of using bioelectrochemical systems (a group of environmentally friendly bio-based technologies with great potential for bioremediation and waste valorisation) for arsenic removal. Previous studies have reported that the spontaneous oxidation of As(III) to As(V) was completely realized in bioelectrochemical systems, however, any of the them succeeded in removing the total arsenic concentration. This study demonstrates that not only it is possible to oxidize As(III) to As(V), but also the total elimination of arsenic can be achieved as the result of intracellular accumulation.SIThis research was possible thanks to the financial support by "Consejeria de Educacion de la Junta de Castilla y Leon" (ref: LE320P18), a project co-financed by FEDER funds. R. M. Alonso thanks the University of Leon for his predoctoral contract. F. Ivars-Barcelo acknowledges the& Spanish "Agencia Estatal de Investigacion" for the Ramon y Cajal excellence grant (Ref.: RYC2020-029470-I/AEI/10.13039/501100011033)

Physical and dynamical characterization of hyperbolic comet C/2017 U7(PANSTARRS)

We present here a dynamical and observational study of the comet C/2017 U7 (PANSTARRS). This comet was discovered in 2017 and found to have a hyperbolic orbit. Our dynamical analysis shows that the object has probably originated in the Oort cloud, however an interstellar origin cannot be discarded. The observations were obtained in 2018 and 2019 using the Goodman High Throughput Spectrograph (GHTS) at the SOAR telescope. We obtained visible spectra covering the wavelength range of and also images in the SDSS filters system. Both the low-resolution reflectance spectrum and the reflectance spectra derived from the SDSS filters show an atypical band at . We conducted a comparative study of the colors and reflectance spectra of different small body populations (e.g., comets, Centaurs, and trans-Neptunian objects or TNOs) from the literature and concluded that the spectra and the colors of this comet are atypical, showing only some overlap with those of some known members of the TNOs and Centaurs, within the large uncertainties of the measurements of those populations. It is found that the feature and overall spectral shape can be reproduced by laboratory spectra of kerite, a template for aliphatic-rich hydrocarbons that has been previously identified in NIR cometary spectra absorptions. It is tentatively proposed that the unusual spectral shape is the result of a particle size distribution of dust grains in the coma or on the surface that has arisen due to a low grain ejection velocity from the surface and large nucleus size