Abstract:Recently, terracotta has attracted interest as low-cost and biocompatible material to build separators in microbial fuel cells (MFCs). However, the influence of a non-conductive material like terracotta on electroactive microbiological communities remains substantially unexplored. This study aims at describing the microbial pools developed from two different seed inocula (bovine and swine sewage) in terracotta-based air-breathing MFC. A statistical approach on microbiological data confirmed different community… Show more
“…2 a), we show the presence of MBA03-dominated (Firmicutes) cluster b I specific to farm reactors, cluster b IV (MSW) where three bacterial orders including Clostridiales , Cloacamonales and Bacteroidales were co-abundant, and WWTP AD-specific cluster b V dominated by Cloacamonales , Clostridiales , Bacteroidales , Sphingobacteriales and Syntrophobacterales . The co-occurrence of MBA03 which was evidenced to be an electroactive genus [ 29 ] and Methanosarcina (see below), might suggest the direct interspecies electron transfer (DIET) to potentially be an effective form of syntrophy in farm methanogenic reactors [ 30 ]. Fig.…”
BackgroundAnaerobic digestion (AD) is a microbe-driven process of biomass decomposition to CH4 and CO2. In addition to renewable and cost-effective energy production, AD has emerged in the European Union as an environmentally friendly model of bio-waste valorisation and nutrient recycling. Nevertheless, due to the high diversity of uncharacterised microbes, a typical AD microbiome is still considered as “dark matter”.ResultsUsing the high-throughput sequencing of small rRNA gene, and a monthly monitoring of the physicochemical parameters for 20 different mesophilic full-scale bioreactors over 1 year, we generated a detailed view of AD microbial ecology towards a better understanding of factors that influence and shape these communities. By studying the broadly distributed OTUs present in over 80% of analysed samples, we identified putatively important core bacteria and archaea to the AD process that accounted for over 70% of the whole microbial community relative abundances. AD reactors localised at the wastewater treatment plants were shown to operate with distinct core microbiomes than the agricultural and bio-waste treating biogas units. We also showed that both the core microbiomes were composed of low (with average community abundance ≤ 1%) and highly abundant microbial populations; the vast majority of which remains yet uncharacterised, e.g. abundant candidate Cloacimonetes. Using non-metric multidimensional scaling, we observed microorganisms grouping into clusters that well reflected the origin of the samples, e.g. wastewater versus agricultural and bio-waste treating biogas units. The calculated diversity patterns differed markedly between the different community clusters, mainly due to the presence of highly diverse and dynamic transient species. Core microbial communities appeared relatively stable over the monitoring period.ConclusionsIn this study, we characterised microbial communities in different AD systems that were monitored over a 1-year period. Evidences were shown to support the concept of a core community driving the AD process, whereas the vast majority of dominant microorganisms remain yet to be characterised.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1195-8) contains supplementary material, which is available to authorized users.
“…2 a), we show the presence of MBA03-dominated (Firmicutes) cluster b I specific to farm reactors, cluster b IV (MSW) where three bacterial orders including Clostridiales , Cloacamonales and Bacteroidales were co-abundant, and WWTP AD-specific cluster b V dominated by Cloacamonales , Clostridiales , Bacteroidales , Sphingobacteriales and Syntrophobacterales . The co-occurrence of MBA03 which was evidenced to be an electroactive genus [ 29 ] and Methanosarcina (see below), might suggest the direct interspecies electron transfer (DIET) to potentially be an effective form of syntrophy in farm methanogenic reactors [ 30 ]. Fig.…”
BackgroundAnaerobic digestion (AD) is a microbe-driven process of biomass decomposition to CH4 and CO2. In addition to renewable and cost-effective energy production, AD has emerged in the European Union as an environmentally friendly model of bio-waste valorisation and nutrient recycling. Nevertheless, due to the high diversity of uncharacterised microbes, a typical AD microbiome is still considered as “dark matter”.ResultsUsing the high-throughput sequencing of small rRNA gene, and a monthly monitoring of the physicochemical parameters for 20 different mesophilic full-scale bioreactors over 1 year, we generated a detailed view of AD microbial ecology towards a better understanding of factors that influence and shape these communities. By studying the broadly distributed OTUs present in over 80% of analysed samples, we identified putatively important core bacteria and archaea to the AD process that accounted for over 70% of the whole microbial community relative abundances. AD reactors localised at the wastewater treatment plants were shown to operate with distinct core microbiomes than the agricultural and bio-waste treating biogas units. We also showed that both the core microbiomes were composed of low (with average community abundance ≤ 1%) and highly abundant microbial populations; the vast majority of which remains yet uncharacterised, e.g. abundant candidate Cloacimonetes. Using non-metric multidimensional scaling, we observed microorganisms grouping into clusters that well reflected the origin of the samples, e.g. wastewater versus agricultural and bio-waste treating biogas units. The calculated diversity patterns differed markedly between the different community clusters, mainly due to the presence of highly diverse and dynamic transient species. Core microbial communities appeared relatively stable over the monitoring period.ConclusionsIn this study, we characterised microbial communities in different AD systems that were monitored over a 1-year period. Evidences were shown to support the concept of a core community driving the AD process, whereas the vast majority of dominant microorganisms remain yet to be characterised.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1195-8) contains supplementary material, which is available to authorized users.
“…Similar approaches in BES field were developed by other research groups, introducing air-water separators (such as terracotta ref [45]) which had the function of hindering water to flow out rapidly and without introducing too high resistance. The 'terracotta' (typical porosity 60-500 nm [3,46]) gets imbibed and acts as porous medium that allows electrolytes mobility. In a previous experiment from our group [33], we employed a ligno-cellulosic biomass (Giant Cane), as separator between electrodes.…”
Section: Rigid and Porous Cylindrical Structurementioning
An innovative low-tech solution to fabricate electro-active biochar (e-biochar) electrodes for bioelectrochemical systems (BES) is proposed. Ligno-cellulosic stalks of Giant Cane (Arundo Donax L.) were subjected to pyrolysis treatment at 900 °C for 1 h. The material kept its original hollow cylindrical shape, rigid morphology and porous texture, as confirmed by 3DX-ray micro-computed tomography. These characteristics are suitable for its use at the air-water interface in BES, as air-breathing bio-cathodes. BET (Brunauer-Emmett-Teller) specific surface area was equal to 114 ± 4 m 2 g-1 , with more than 95% of pores in the microporosity range (pore diameter < 1 nm). Surface electrocatalytic activity was sufficient to sustain oxygen reduction reaction at pH 7, in terms of both onset potential (-0.02 V vs Ag/AgCl) and reduction limiting current density (1 A m-2). Electrical resistivity measurements confirmed sufficient conductivity (8.9×10 −3 ± 1×10 −4 m) of the material and Raman spectroscopy allowed to estimate a graphitization degree in relation to the ID/IG, equal to 2.26. In parallel, the e-biochar were tested as airexposed bio-cathodes in BES, coupled to carbon cloth bio-anodes. After inoculation with wastewater from swine-farming, current densities were generated in the range of 100-150 mA m-2 , along more than 2 2 months of operation, under sodium acetate feeding. Confocal laser scanning imaging revealed consistent biofilm formation on the water-side surface of the cathodes, while a nearly-complete absence of it at the air-side. These e-biochar electrodes might open innovative perspectives to scale-up BES for different applications. Here, consistent salts depositions on the material after 70 days of exposure to the wastewater, suggest that e-biochar biocathodes might serve to recycle nutrients to agricultural soils, through mineralsenriched biochar. 1. INTRODUCTION Real scale application of bio-electrochemical systems (BES) has been facing the need to find an optimal balance between processes efficiencies and costs. Many researches are addressing to develop low-cost and environmentally-compatible materials to fabricate electrodes for large scale applications, such as wastewater treatment, soil bioremediation, etc. [1-3]. To date, the most competitive materials are based on carbon and include graphite-based rods, fiber brushes and granules, carbon-fiber cloths, carbon paper sheets, carbon felt and reticulated vitreous carbon [1,2,4]. They are selected due to their strong biocompatibility and inert properties at room temperature. The use of such materials as air-breathing cathodes has been coupled to the fabrication of microporous layers, made of activated carbon, pressed on carbon cloths (or other current collector) in the presence of polymeric binders (Nafion, PTFE, etc.) [5,6]. High surface area favors the cathodic oxygen reduction reaction (ORR) that needs the simultaneous presence of solid, liquid and gaseous phases. Microporous layers also act as gas diffusion layer at air-water interface, because the p...
“…Several enzymes have been exploited as catalysts for ORR in neutral media with the superb performance, but both high cost and low durability make those materials unsuitable for MFCs applications [ 47 ]. Microbial catalysts (aerobic [ 48 ] and anaerobic [ [49] , [50] , [51] ]) are also studied, and it was found that they enhance the ORR of graphite-based cathodes. Still, the mechanism is quite complex and not completely understood.…”
Iron aminoantipyrine (Fe-AAPyr), graphene nanosheets (GNSs) derived catalysts and their physical mixture Fe-AAPyr-GNS were synthesized and investigated as cathode catalysts for oxygen reduction reaction (ORR) with the activated carbon (AC) as a baseline. Fe-AAPyr catalyst was prepared by Sacrificial Support Method (SSM) with silica as a template and aminoantipyrine (AAPyr) as the organic precursor. 3D-GNS was prepared using modified Hummers method technique. The Oxygen Reduction Reaction (ORR) activity of these catalysts at different loadings was investigated by using rotating ring disk (RRDE) electrode setup in the neutral electrolyte. The performance of the catalysts integrated into air-breathing cathode was also investigated. The co-presence of GNS (2 mg cm−2) and Fe-AAPyr (2 mg cm−2) catalyst within the air-breathing cathode resulted in the higher power generation recorded in MFC of 235 ± 1 μW cm−2. Fe-AAPyr catalyst itself showed high performance (217 ± 1 μW cm−2), higher compared to GNS (150 ± 5 μW cm−2) while AC generated power of roughly 104 μW cm−2.
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