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Este artículo ilustra el proceso de escalado de la tecnología MDC (microbial desalination cell o celda de desalación microbiana) para el tratamiento de aguas, desde su concepción hace escasamente 10 años, capaz de tratar escasos mililitros, hasta la reciente construcción de la primera unidad piloto capaz de desalar hasta 3,6 m3/día.

Lack of suitable electron donors or acceptors is in many cases the key reason for pollutants to persist in the environment. Externally supplementation of electron donors or acceptors is often difficult to control and/or involves chemical additions with limited lifespan, residue formation or other adverse side effects. Microbial electrochemistry has evolved very fast in the past years - this field relates to the study of electrochemical interactions between microorganisms and solid-state electron donors or acceptors. Current can be supplied in such so-called bioelectrochemical systems (BESs) at low voltage to provide or extract electrons in a very precise manner. A plethora of metabolisms can be linked to electrical current now, from metals reductions to denitrification and dechlorination. In this perspective, we provide an overview of the emerging applications of BES and derived technologies towards the bioremediation field and outline how this approach can be game changing This work was funded through the European Union’s Horizon 2020project ELECTRA under grant agreement No. 826244 and National Natural Science Foundation of China (NSFC) (No. 31861133001,31861133002, 31861133003). S.P is a Serra Húnter Fellow (UdG-AG-575) and acknowledges the funding from the ICREA Acad emia award.LEQUiA has been recognized as consolidated research group by theCatalan Government with code 2017-SGR-1552. KR is supported by theGhent University special research fund under grant No. BOF19/GOA/026

METland is a new variety of Constructed Wetland (CW) for treating wastewater where gravel is replaced by a biocompatible electroconductive material to stimulate the metabolism of electroactive bacteria. The system requires a remarkably low land footprint (0.4 m2/pe) compared to conventional CW, due to the high pollutant removal rate exhibited by such microorganisms. In order to predict the optimal locations for METland, a methodology based on Multi-Criteria Evaluation (MCE) techniques applied to Geographical Information Systems (GIS) has been proposed. Seven criteria were evaluated and weighted in the context of Analytical Hierarchy Process (AHP). Finally, a Global Sensitivity Analysis (GSA) was performed using the Sobol method for resource optimization. The model was tested in two locations, oceanic and Mediterranean, to prove its feasibility in different geographical, demographic and climate conditions. The GSA revealed as conclusion the most influential factors in the model: (i) land use, (ii) distance to population centers, and (iii) distance to river beds. Interestingly, the model could predict best suitable locations by reducing the number of analyzed factors to just such three key factors (responsible for 78% of the output variance). The proposed methodology will help decision-making stakeholders in implementing nature-based solutions, including constructed wetlands, for treating wastewater in rural areas.

Erratum regarding missing Declaration of Competing Interest statements in previously published articles.

Las aguas residuales urbanas recogen la mayor parte de los desechos orgánicos generados por la acción humana. Para reducir el impacto de la contaminación sobre el ambiente (ríos, acuíferos, suelos, etc.) se requiere un tratamiento efectivo antes de su vertido.

Microbial Desalination Cell (MDC) represents an innovative technology which accomplishes simultaneous desalination and wastewater treatment without external energy input. MDC technology could be employed to provide freshwater with low-energy input, for example, in remote areas where organic wastes (i.e., urban or industrial) are available. In addition, MDC technology has been proposed as pre-treatment in conventional reverse osmosis plants, with the aim of saving energy and avoiding greenhouse gases related to conventional desalination processes. The use of oxygen reduction (i.e. O2 + 2H2O + 4e− → 4 OH−, E0′ = 0.815 V, pH = 7) was usually implemented as cathodic reaction in most of the MDCs reported in literature, whereas other strategies based on liquid catholytes have been also proposed, for example, ferro-ferricyanide redox couple (i.e. Fe(CN)3−6 + 1e− → Fe(CN)4−6 , E0 = 0.37 V). As the MDC designs in the literature and operation modes (i.e., batch, continuous, semi-continuous, etc.) are quite different, the available MDC studies are not directly comparable. For this reason, the main objective of this work was to have a proper comparison of two similar MDCs operating with two different catholyte strategies, and compare performance and desalination efficiencies. In this sense, this study compares the desalination performance of two laboratory-scale MDCs located in two different locations for brackish water and sea water using two different strategies. The first strategy consisted of an air cathode for efficient oxygen reduction, while the second strategy was based on a liquid catholyte with Fe3+/Fe2+ solution (i.e., ferro-ferricyanide complex). Both strategies achieved desalination efficiency above 90% for brackish water. Nominal desalination rates (NDR) were in the range of 0.17–0.14 L·m−2·h−1 for brackish and seawater with air diffusion cathode MDC, respectively, and 1.5–0.7 L·m−2·h−1 when using ferro-ferricyanide redox MDC. Organic matter present in wastewater was effectively removed at 0.9 and 1.1 kg COD·m−3·day−1 using the air diffusion cathode MDC for brackish and sea water, respectively, and 7.1 and 19.7 kg COD·m−3·day−1 with a ferro-ferricyanide redox MDC. Both approaches used a laboratory MDC prototype without any energy supply (excluding pumping energy). Pros and cons of both strategies are discussed for subsequent upscaling of MDC technology.

La industria alimentaria española es el primer sector industrial del país experimentando una expansión progresiva por quinto año consecutivo, según los datos de la Federación Española de Industrias de Alimentación y Bebidas (FIAB). En concreto, el sector cervecero tiene un papel clave en el panorama agroalimentario, con una facturación cercana al sector del vino y del aceite de oliva. Para llevar a cabo su actividad, este tipo de industria requiere grandes volúmenes de agua, que al final de proceso se transforman en agua residual que debe ser convenientemente tratada para cumplir con las normativas legales europeas y españolas.

El proyecto Life-ANSWER (soluciones avanzadas de nutrientes con recuperación electroquímica) tiene como objetivo proporcionar una tecnología innovadora que integre la electrocoagulación y la electroquímica microbiana para el tratamiento de aguas residuales de la industria agroalimentaria. El sistema ANSWER permite reutilizar el agua tratada, produciendo biogás enriquecido (CH4 + H2) y fertilizante a partir del agua residual.

Domestic and industrial wastewaters contain organic substrates and nutrients that can be recovered instead of being dissipated by emerging efficient technologies. The aim of this study was to promote bio-hydrogen production and carbon fixation using a mixed culture of purple phototrophic bacteria (PPB) that use infrared radiation in presence or absence of an electrode as electron donor. In order to evaluate the hydrogen production under electrode-free conditions, batch experiments were conducted using different nitrogen (NH4Cl, Na-glutamate, N2 gas) and carbon sources (malic-, butyric-, acetic- acids) under various COD:N ratios. Results suggested that the efficiency of PPB to produce biogenic H2 was highly dependent on the substrates used. The maximum hydrogen production (H2_max, 423 mLH2/L) and production rate (H2_rate, 2.71 mLH2/Lh) were achieved using malic acid and Na-glutamate at a COD:N ratio of 100:15. Under these optimum conditions, a significant fixation of nitrogen in form of single-cell proteins (874.4 mg/L) was also detected. Under bio-electrochemical conditions using a H-cell bio-electrochemical device, the PPB were grown planktonic in the bio-cathode chamber with the optimum substrate ratio of malic acid and Na-glutamate. A redox potential of −0.5 V (vs. Ag/AgCl) under bio-electrochemical conditions produced comparable amounts of bio-hydrogen but significantly negligible traces of CO2 as compared to the biological system (11.8 mLCO2/L). This suggests that PPB can interact with the cathode to extract electrons for further CO2 re-fixation (coming from the Krebs cycle) into the Calvin cycle, thereby improving the C usage. It has also been observed during cyclic voltammograms that a redox potential of −0.8 V favors considerably the electrons consumption by the PPB culture, suggesting that the PPB can use these electrons to increase the biohydrogen production. These results are expected to prove the feasibility of stimulating PPB through bio-electrochemical processes in the production of H2 from wastewater resources, which is a field of special novelty and still unexplored.

A microbial electrochemical-based constructed wetland (METland) is a wetland variation that relies on the presence of electroactive bacteria (EAB) to enhance the degradation of compounds of interest. Compared with CW- microbial fuel cell (CW-MFC), a METland is designed in a short-circuit mode (no electrodes connected by external circuit) using an electro-conductive substrate as single-piece electrode. The major challenge in this system is to correlate the EAB metabolism with pollutant removal. In environments with the presence of EAB, electric fields are created by anodic and cathodic reactions, promoting local charge imbalance, therefore generating ionic and electron fluxes. The fluxes generated in a METland can be quantified by measuring the electric potentials (EP) with sensors non-sensible to redox-active compounds, and able to detect low current signals in highly conductive matrixes. Based the hypothesis that electron fluxes detected with the aid of EP sensors can be correlated with high removal rates of pollutants, our research tested the removal of organic matter in a real scale METland system, and the correlation with the electron fluxes generated by the presence of EAB.

Microbial electrochemical technologies (MET) rely on the presence of the metabolic activity of electroactive bacteria for the use of solid-state electrodes for oxidizing different kinds of compound that can lead to the synthesis of chemicals, bioremediation of polluted matrices, the treatment of contaminants of interest, as well as the recovery of energy. Keeping these possibilities in mind, there has been growing interest in the use of electrochemical technologies for wastewater treatment, if possible with simultaneous power generation, since the beginning of the present century. In the last few years, there has been growing interest in exploring the possibility of merging MET with constructed wetlands offering a new option of an intensified wetland system that could maintain a high performance with a lower footprint. Based on that interest, this paper explains the general principles of MET, and the different known extracellular electron transfer mechanisms ruling the interaction between electroactive bacteria and potential solid-state electron acceptors. It also looks at the adoption of those principles for the development of MET set-ups for simultaneous wastewater treatment and power generation, and the challenges that the technology faces. Ultimately, the most recent developments in setups that merge MET with constructed wetlands are presented and discussed.

Method of desalination and wastewater treatment in a microbial desalination cell reactor, the microbial desalination cell reactor comprises three compartments, an anodic compartment, a cathodic compartment and a saline compartment, the method comprising: (a) adding electrically conductive particles or electrically conductive material in the anodic compartment and cathodic compartment, (b) adding bacteria species of the genus Geobacter in the anodic compartment, adding an aqueous solution of a sulphate salt as catholyte, adding saline solution to the saline compartment (c) applying an external power supply to desalinate the saline solution (d) when constant electric current is achieved, replacing the solution in the cathodic compartment by a hypochlorite solution and replacing the external power supply by an external circuit or connecting anode and cathode to produce short circuit conditions and (d) oxidizing organic matter present in wastewater by bacteria from the genus Geobacter in the anodic compartment and desalinating the solution in the saline compartment and (e) after 20 to 30 operation cycles, replacing the saline solution by a second solution of hypochlorite salt to provide cleaning in place.

Geobacter sulfurreducens (Gs) attachment and biofilm formation on self-assembled monolayers (SAMs) of carboxyl-terminated alkanethiol linkers with varied chain length on gold (Au) was investigated by electrochemical and microscopic methods to elucidate the effect of the surface modification on the current production efficiency of Gs cells and biofilms. At the initial stage of the cell attachment, the electrochemical activity of Gs cells at a submonolayer coverage on the SAM-Au surface was independent of the linker length. Subsequently, multiple potential cyclings indicated that longer linkers provided more biocompatible conditions for Gs cells than shorter ones. For Gs biofilms, on the other hand, the turnover current decreased exponentially with the linker length. During the biofilm formation, bacteria need to adjust from the initial planktonic state to an electrode-respiring state, which was triggered by a strong electrochemical stress found for shorter linkers, resulting in the formation of mature biofilms. Our results suggest that the initial cell attachment and the biofilm formation are two inherently different processes. Therefore, the effects of linker molecules, electron transfer efficiency and biocompatibility, must be explored simultaneously to understand both processes to increase the current production of electrogenic microorganisms in microbial fuel cells.

The scaling-up process of microbial electrochemical technologies (METs) may require an initial investment for constructing completely new infrastructure. In contrast, adapting METs to equipment already present in wastewater treatment plants (WWTP) can be an attractive alternative to accelerate their implementation. In this study we evaluated the viability of adapting a classical oxic–anoxic chamber system to a membrane-free microbial electrochemical system in order to remove both nitrogen and organic matter. We simulated this configuration on a 22 L reactor with two chambers in the absence of any separation membrane. The working electrode acted as the electron source for denitrifying microorganisms and was placed in the first chamber. The system was able to support the nitrifying activity without external aeration and at oxygen levels below 2 mg L−1. The influent, a synthetic medium with ammonium as the sole nitrogen source, was fed at COD/N ratios from 2 to 4. Up to 19 g NO3− N m−3 TCC per day were reduced at a COD/N ratio of 4, with a denitrification efficiency of 93% and a nitrogen removal efficiency of 81%. The system's capacity for nitrifying and denitrifying was strongly dependent on both the COD/N ratio and the working electrode potential. A massive sequencing study revealed the greater abundance of denitrifying genera such as Opitutos, Methyloversa and Zoogloea at the cathode. Nitrifying genera such as Nitrosomonas and Nitrospira were found in the reactor, the latter being enriched at the anode. In this study we demonstrate that the classical configuration of activated sludge systems can be turned into a MET to treat wastewater. We suggest the implementation of this air-free hybrid configuration in WWTP as an alternative method to remove nutrients from effluents with low levels of organic matter.

In this study, we designed a microbial electrochemical fluidized bed reactor (ME-FBR), with an electroconductive anodic bed made of activated carbon particles for treating a brewery wastewater. Under a batch operating mode, acetate and propionate consumption rates were 13-fold and 2.4-fold higher, respectively, when the fluidized anode was polarized (0.2 V) with respect to open circuit conditions. Operating in a continuous mode, this system could effectively treat the brewery effluent at organic loading rates (OLR) over 1.7 kg m-3NRV d-1 and with removal efficiencies of 95 ± 1.4% (hydraulic retention time of 1 day and an influent of 1.7 g-COD L-1). The coulombic efficiency values highly depended upon the OLR applied, and varied from a 56 ± 15% to 10 ± 1%. Fluorescence in situ hybridization (FISH) analysis revealed a relative high abundance of Geobacter species (ca. 20%), and clearly showed a natural microbial stratification. Interestingly, the Geobacter cluster was highly enriched in the innermost layers of the biofilm (thickness of 10 μm), which were in contact with the electroconductive particles of bed, whereas the rest of bacteria were located in the outermost layers. To our knowledge, this is the first time that such a clear microbial stratification has been observed on an anode-respiring biofilm. Our results revealed the relevant role of Geobacter in switching between the electrode and other microbial communities performing metabolic reactions in the outermost environment of the biofilm.

International audience; Microbial electrochemical technologies (METs) rely on the control of interactions between microorganisms and electronic devices, enabling to transform chemical energy into electricity. We report a new approach to construct ready-to-use artificial bioelec-trodes by immobilizing Geobacter sulfurreducens cells in composite materials associating silica gel and carbon felt fibres. Viability test confirmed that the majority of bacteria (ca. 70 AE 5%) survived the encapsulation process in silica and that cell density did not increase in 96 h. The double entrapment within the silica–carbon composite prevented bacterial release from the electrode but allowed a suitable mass transport (ca. 5 min after electron donor pulse), making the electrochemical characterization of the system possible. The artificial bioelectrodes were evaluated in three-electrode reactors and the maximum current displayed was ca. 220 and 150 lA cm À3 using acetate and lactate as electron donors respectively. Cyclic voltammetry of acetate-fed bioelectrodes revealed a sigmoidal catalytic oxidation wave, typical of more advanced-stage bio-films. The presence of G. sulfurreducens within composites was ascertained by SEM analysis, suggesting that only part of the bacterial population was in direct contact with the carbon fibres. Preliminary analyses of the transcriptomic response of immobilized G. sulfurreducens enlightened that encapsula-tion mainly induces an osmotic stress to the cells. Therefore, ready-to-use artificial bioelectrodes represent a versatile time-and cost-saving strategy for microbial electrochemical systems.

The absence of suitable terminal electron acceptors (TEA) in soil might limit the oxidative metabolism of environmental microbial populations. Bioelectroventing is a bioelectrochemical strategy that aims to enhance the biodegradation of a pollutant in the environment by overcoming the electron acceptor limitation and maximizing metabolic oxidation. Microbial electroremediating cells (MERCs) are devices that can perform such a bioelectroventing. We also report an overall profile of the (14) C-ATR metabolites and (14) C mass balance in response to the different treatments. The objective of this work was to use MERC principles, under different configurations, to stimulate soil bacteria to achieve the complete biodegradation of the herbicide (14) C-atrazine (ATR) to (14) CO2 in soils. Our study concludes that using electrodes at a positive potential [+600mV (versus Ag/AgCl)] ATR mineralization was enhanced by 20-fold when compared to natural attenuation in electrode-free controls. Furthermore, ecotoxicological analysis of the soil after the bioelectroventing treatment revealed an effective clean-up in

4th EU-ISMET 2018, Newcastle upon Tyne (United Kingdom) from 12th to 14th September 2018 This activity is supported by the Spanish Ministry of Education through the FPU scholarship (FPU14/05457) This activity is supported by the Spanish Ministry of Education through the FPU scholarship (FPU14/05457)

Para transmitir conceptos científicos complejos en un entorno escolar, la utilización de experimentos llamativos representa una herramienta muy útil. En este artículo se presenta la columna bioelectrogénica, un sistema experimental que une la columna de Winogradsky clásica con las más recientes investigaciones en el campo de la microbiología aplicada. A través de su implementación es posible visualizar procesos físicos, químicos y biológicos que forman parte de la enseñanza científica en institutos de secundaria. Además, la columna bioelectrogénica ha sido ideada para demostrar la existencia de bacterias capaces de producir energía eléctrica, un fenómeno que induce curiosidad y estupor, elementos claves para estimular la participación de los estudiantes. Este sistema ha sido presentado en varias actividades de divulgación para estudiantes de secundaria y siempre ha despertado un elevado grado de interés., The use of inspiring experimental demonstrations is a fundamental tool for teaching complex scientific concepts in secondary schools. In this article we present the bioelectrogenic column, an experimental system that joins the classic Winogradsky column to the most recent findings in the field of applied microbiology. With this system we can visualise physical, chemical and biological processes that are at the heart of a sound scientific education. Furthermore, the bioelectrogenic column had been designed to demonstrate the existence of bacteria capable of producing electric energy, an astonishing phenomenon that leaves students highly inquisitives, a key for stimulating their participation. This system has been presented in various scientific outreaching activities for secondary school, always awakening a strong interest in the audience.

The ability of Geobacter species to transfer electrons outside the cell enables them to play an important role in a number of biogeochemical and bioenergy processes. Gene deletion studies have implicated periplasmic and outer-surface c-type cytochromes in this extracellular electron transfer. However, even when as many as five c-type cytochrome genes have been deleted, some capacity for extracellular electron transfer remains. In order to evaluate the role of c-type cytochromes in extracellular electron transfer, Geobacter sulfurreducens was grown in a low-iron medium that included the iron chelator (2,2'-bipyridine) to further sequester iron. Haem-staining revealed that the cytochrome content of cells grown in this manner was 15-fold lower than in cells exposed to a standard iron-containing medium. The low cytochrome abundance was confirmed by in situ nanoparticle-enhanced Raman spectroscopy (NERS). The cytochrome-depleted cells reduced fumarate to succinate as well as the cytochrome-replete cells do, but were unable to reduce Fe(III) citrate or to exchange electrons with a graphite electrode. These results demonstrate that c-type cytochromes are essential for extracellular electron transfer by G. sulfurreducens. The strategy for growing cytochrome-depleted G. sulfurreducens will also greatly aid future physiological studies of Geobacter species and other microorganisms capable of extracellular electron transfer.

We have explored a new concept in bacteria-electrode interaction based on the use of fluid-like electrodes and planktonic living cells. We show for the first time that living in a biofilm is not a strict requirement for Geobacter sulfurreducens to exchange electrons with an electrode. The growth of planktonic electroactive G. sulfurreducens could be supported by a fluid-like anode as soluble electron acceptors and with electron transfer rates similar to those reported for electroactive biofilms. This growth was maintained by uncoupling the charge (catabolism) and discharge (extracellular respiration) processes of the cells. Our results reveal a novel method to culture electroactive bacteria in which every single cell in the medium could be instantaneously wired to a fluid-like electrode. Direct extracellular electron transfer is occurring but with a new paradigm behind the bacteria-electrode interaction.

Microbial Desalination Cells constitute an innovative technology where microbial fuel cell and electrodialysis merge in the same device for obtaining fresh water from saline water with no energy-associated cost for the user. In this work, an anodic biofilm of the electroactive bacteria Geobacter sulfurreducens was able to efficiently convert the acetate present in synthetic waste water into electric current (j = 0.32 mA cm−2) able to desalinate water. .Moreover, we implemented an efficient start-up protocol where desalination up to 90% occurred in a desalination cycle (water production:0.308 L m−2 h−1, initial salinity: 9 mS cm−1, final salinity

Sistema bioelectroquímico para depurar aguas residuales, que comprende una cámara anaerobia anódica, en la que se produce la oxidación de materia orgánica por microorganismos, y una cámara aerobia catódica, donde el cátodo de dicha cámara aerobia catódica consiste en esferas conductoras flotantes.

(Figure Presented) Down to the wire: electro-active bacteria that exchange electrons with solid electrodes are studied by electrochemical and infrared techniques. The approach allows the identification of cell-surface molecules involved in the direct electron transfer to the electrode, a development that is crucial for future utilization of these electricity-producing microorganisms. Fil: Busalmen, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Esteve Núñez, Abraham. Universidad de Alicante; España Fil: Berná Galiano, Antonio. Universidad de Alicante; España Fil: Miguel Feliu, Juan. Universidad de Alicante; España

A novel fluorescence technique for monitoring the redox status of c-type cytochromes in Geobacter sulfurreducens was developed in order to evaluate the capacity of these extracytoplasmic cytochromes to store electrons during periods in which an external electron acceptor is not available. When intact cells in which the cytochromes were in a reduced state were excited at a wavelength of 350 nm, they fluoresced with maxima at 402 and 437 nm. Oxidation of the cytochromes resulted in a loss of fluorescence. This method was much more sensitive than the traditional approach of detecting c-type cytochromes via visible light absorbance. Furthermore, fluorescence of reduced cytochromes in individual cells could be detected via fluorescence microscopy, and the cytochromes in a G. sulfurreducens biofilm, remotely excited with an optical fibre, could be detected at distances as far as 5 cm. Fluorescence analysis of cytochrome oxidation and reduction of the external electron acceptor, anthraquinone-2,6-disulfonate, suggested that the extracytoplasmic cytochromes of G. sulfurreducens could store approximately 10(7) electrons per cell. Independent analysis of the haem content of the cells determined from analysis of incorporation of (55)Fe into cytochromes provided a similar estimate of cytochrome electron-storage capacity. This electron-storage capacity could, in the absence of an external electron acceptor, permit continued electron transfer across the inner membrane sufficient to supply the maintenance energy requirements for G. sulfurreducens for up to 8 min or enough proton motive force to power flagella motors for G. sulfurreducens motility. The fluorescence approach described here provides a sensitive method for evaluating the redox status of Geobacter species in culture and/or its environments. Furthermore, these results suggest that the periplasmic and outer-membrane cytochromes of Geobacter species act as capacitors, allowing continued electron transport, and thus viability and motility, for Geobacter species as they move between heterogeneously dispersed Fe(III) oxides during growth in the subsurface.

The absence of suitable terminal electron acceptors (TEA) in soil might limit the oxidative metabolism of environmental microbial populations. Microbial electroremediating cells (MERCs) consist in a variety of bioelectrochemical devices that aim to overcome electron acceptor limitation and maximize metabolic oxidation with the purpose of enhancing the biodegradation of a pollutant in the environment. The objective of this work was to use MERCs principles for stimulating soil bacteria to achieve the complete biodegradation of the herbicide (14) C-isoproturon (IPU) to (14) CO2 in soils. Our study concludes that using electrodes at a positive potential [+600mV (versus Ag/AgCl)] enhanced the mineralization by 20-fold respect the electrode-free control. We also report an overall profile of the (14) C-IPU metabolites and a (14) C mass balance in response to the different treatments. The remarkable impact of electrodes on the microbial activity of natural communities suggests a promising future for this emerging environmental technology that we propose to name bioelectroventing.