Electromethanogenesis for the conversion of hydrothermal carbonization exhaust gases into methane

[EN] Hydrothermal carbonization (HTC) is a biomass conversion process that generates a CO2-rich gaseous phase that is commonly released directly into the atmosphere. Microbial electromethanogeneis (EM) can potentially use this off-gas to convert the residual CO2 into CH4, thus avoiding GHG emissions while adding extra value to the overall bioprocess. In the present work, the HTC gas phase was fed to two mixed-culture biocathodes (replicates) polarized at −1.0V vs. Ag/AgCl. Compared to pure CO2, HTC gas had a marked negative effect on the process, decreasing current density by 61%, while maximum CH₄ yield contracted up to 50%. HTC also had an unequal impact on the cathodic microbial communities, with the methanogenic hydrogenotrophic archaea Methanobacteriaceae experiencing the largest decline. Despite that, the present study demonstrates that HTC can be used in EM as a raw material to produce a biogas with a methane content of up to 70%.S

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

Charge storage capacity of electromethanogenic biocathodes

[EN] Methanogenic biocathodes (MB) can convert CO2 and electricity into methane. This feature, that allows them to potentially be used for long-term electrical energy storage, has aroused great interest during the past 10 years. MB can also operate as biological supercapacitors, a characteristic that can be exploited for short-term energy storage and that has received much less attention. In this study, we investigate the electrical charge storage capabilities of carbon-felt-based MB modified with graphene oxide. The charge-discharge experiments revealed that the potential of the electrode plays an important role during the discharging period: low potentials (−1.2 V vs Ag/AgCl) created an inrush of faradaic current that masked any capacitive current. At more positive potentials (−0.8 V vs Ag/AgCl), the biological electrodes were outperformed by the abiotic electrodes, and only when the potential was set at −1.0 V vs Ag/AgCl the graphene-modified biological electrode showed its superior charge storage capacity. Overall, results indicated that the graphene modification is crucial to obtain bioelectrodes with improved capacitance: untreated bioelectrodes showed a charge storage capacity inferior to that measured in the abiotic electrodes.SIMCIN/AEI/10.13039/501100011033European Union NextGenerationEU/PRT

Alternative start-up strategies for the Bioelectrosynthesis of acetate

Carbon capture and utilization at biocathodes provides a solution to minimize CO2 emissions meanwhile commodity chemicals are being generating from an inexpensive substrate. The aim of this work is to develop biocathodes for MES systems capable of making use of CO2 in order to generate valuable chemicals. The biocathodes were inoculated using two different inocula and following two different strategies. These different start-up conditions showed distinct electrical behavior in three of the four cases. These microbial electro-synthesis systems (MES) were capable of achieving an acetic acid production between 70-196mg/L depending on the strategy. The use of a river mud inoculum resulted in a sharp enrichment, and when the potential was invert to force it to work as a biocathode, the biofilm got mostly specific in acetic acid producing bacteria, Acterobacteraceae, and some hydrogen generating bacteria. The hydrogenotrophic methanogen Methanobacteriaceae, was the only family identified on the cathode. However, the use of an anaerobic digestion inoculum resulted in a highly diverse biofilm and in a lower acetic acid production with hydrogen detected. The Archaeal population was inhibited under this condition. To conclude it is observed that specialisation of biofilm in certain Eubacterial families improves bioelectrosynthesis, and acetic acid production in particular. In addition, it is highlighted that being the Archaeal community quite similar within both biofilms, the dominant families on the cathode biofilms were drastically different, likely due to the difference in the Eubacterial microorganisms. Thanks “Junta de Castilla y Leon” for postdoctoral contract associated to project ref: LE060U16. The authors acknowledge the funding of the Spanish “Ministerio de Economía y Competitividad” via project CTQ2015-68925-R

Reduced graphene oxide improves the performance of a methanogenic biocathode

.Microbial electrosynthesis (MES), a sub-branch of bioelectrochemical processes, takes advantage of a certain type of electroactive microorganism to produce added value products (such as methane) from carbon dioxide (CO2). The aim of this study is to quantify the benefits of using a carbon felt electrode modified with reduced graphene-oxide (rgoCF) as a methanogenic biocathode. The current density generated by the rgoCF was almost 30% higher than in the control carbon felt electrode (CF). In addition, charge transfer and ohmic resistances were, on average, 50% lower in the rgoCF electrode. These improvements were accompanied by a larger presence of bacteria (31% larger) and archaea (18% larger) in the rgoCF electrode. The microbial communities were dominated by hydrogenotrophic methanogenic archaea (Methanobacterium) and, to a lesser extent, by a low-diversity group of bacteria in both biocathodes. Finally, it was estimated that for a CO2 feeding rate in the range 15–30 g CO2 per m2 of electrode per day, it is possible to produce a high-quality biogas (>95% methane concentrationS

Understanding nitrogen recovery from wastewater with a high nitrogen concentration using microbial electrolysis cells

9 p.This study was aimed at understanding the effect of applied voltage, catholyte and reactor scale on nitrogen recovery from two different organic wastes (digestate and pig slurry) by means of microbial electrolysis cell (MEC) technology. For this purpose, MEC sizes of 100, 500 and 1000 mL were tested at applied voltages of 0.6, 1 and 1.4 V using either a phosphate-buffered solution or NaCl solution as the catholyte. By increasing the reactor size from 500 mL to 1000 mL, a decrease in the ammonia recovery efficiency from 47 to 42 % was observed. The results also showed that the phosphate-buffered solution is preferable as the catholyte and that the voltage applied does not have a noticeable effect on current production and ammonia recovery. Low biodegradability of the wastes was identified as the main bottleneck. This research was supported by the European Union Horizon 2020 Research and Innovation Programme (GA nº 668128-Newfert-H2020-BBI-PPP-2014-1). Financing: This project has received funding from the Bio Based Industries Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No 66812

Electrodos de carbono modificados por electro-reducción de óxido de grafeno para su aplicación en sistemas bio-electroquímicos

Modificación de electrodos de carbono con óxido de grafeno para la mejora del rendimiento en sistemas bioelectroquímicos. This research was supported by the regional government ‘Junta de Castilla y León, Consejería de Educación’, project reference: LE060U16, co-financed by FEDER fund

The impact of externally added hydrogen gas on microbial electrosynthesis from CO2

Hydrogen is a key versatile biomolecule in microbial electrosynthesis (MES). It can be directly produced by electrolysis to be used as an intermediate, directly biosynthesize by electroactive microorganisms from protons and electrons, or externally added to drive other bioelectrochemical or biological reactions. The aim of this study is to bring further understanding on how externally added hydrogen impacts product formation on MES. Two double-chamber microbial electrolysis cells were built in 500mL modified Schott-Duran bottles (Figure 1A). The cathode consisted of a 175 cm2 carbon felt (+1V vs. Ag/AgCl) and a platinum wire was used as counter electrode. The cathode was inoculated according to the procedure detailed in Bajracharya et al. 2017, and following the acclimation period the biocathode was fed with a gas mixture containing 20% H2 / 20% N2 / 60% CO2. After 2 weeks of operation hydrogen was removed from the feed ( 20% N2 / 80% CO2). When the cell was fed with the hydrogen-containing mixture, acetate and ethanol concentrations (Figure 1B) grew steadily with time (composition ratio around 1:1 (w/w)). This behavior suggested that hydrogen was acting as a reducing agent driving direct production of ethanol, or even its production from acetate. However, when hydrogen was removed from the feed, ethanol concentration declined, while acetate concentration sharply increased showing CO2-acetate selectivities near 100%. These results indicate how ethanol production is highly dependent on externally-added hydrogen, while the synthesis of acetate only requires the cathode as a source of electrons. A.Sotres thanks “Junta de Castilla y Leon” for postdoctoral contract associated to project ref: LE060U16, cofinanced by FEDER fund

Development of a critical structure state alarm system based on the instrumentation of the Botafoc breakwater nº 8 caisson

Balearic Port Authority has developed an instrumentation system for the #8 caisson of the Botafoc breakwater that integrates 12 pressure sensors located at three surfaces, two in contact with the sea water and another with the bottom. This design was completed with an inertial system that measures the angular velocities and the accelerations over the three Cartesian axes. Consequently, the system measures actions (pressures) and reactions (movements and accelerations) experimented by the caisson, due to sea waves and/or other service loads. R+D department of the Port Authority and Polytechnic University of Madrid are working on two directions, the development of new theories on vertical breakwater design that go beyond Goda and Sainflou, and on the creation of a real-time critical structure alarm system, based on the instrumentation installed. This alarm system has two main parts: the instrumentation itself that collects data and processes it on real-time (the data processing compares the pressure law suffered by the caisson in every step process with the design critical state of the caisson, in this case the Goda pressure law for a 6.5 m wave), giving a security coefficient that points out the risk level on real-time; and the alarm system consisting of a monitoring panel located in the Port Control Center that shows the risk level and advises in case of an incidental evacuation of this critical portuary installation

Pilot-scale bioelectrochemical system for simultaneous nitrogen and carbon removal in urban wastewater treatment plants

[EN] This study aims to characterize the performance of a 150 L bioelectrochemical system-based plant, during the simultaneous carbon and nitrogen removal from several waste streams of wastewater treatment plants. The bioelectrochemical system (BES) contained five electrode pairs (operated hydraulically and electrically in parallel) and was fed with either wastewater, centrate (nutrient-rich liquid stream produced during the dewatering of digested biomass), or a mixture of both over 63 days, with a hydraulic retention time of one day. Total organic carbon and total nitrogen removal rates averaged 80% and 70%, respectively, with a specific energy consumption of 0.18 kWh·m−3 (BES + ancillary equipment). This work also underlines the challenges of using BES for nitrogen removal, highlighting the limitations of the current design, and suggesting some strategies for improvement.SIMinisterio de Educación, Cultura y Deport