• Energy Research

Abstract Mechanisms underlying plant succession remain highly debated. A global quantification of the relative importance of species addition versus replacement is lacking due to the local scope of most studies. We quantified their role in the variation of plant communities colonizing the forelands of 46 retreating glaciers distributed worldwide, using both environmental DNA and traditional surveys. Both mechanisms concur in determining community changes over time but their relative importance varied over time along successions. Taxa addition predominated immediately after glacier retreat, as expected in harsh environments, while replacement became more important for late-successional communities. Those changes were aligned with total beta-diversity changes, which were larger between early successional communities than between late-successional communities (>50 years since glacier retreat). Despite the complexity of community assembly over plant succession, our global pattern suggests a generalized shift from the dominance of facilitation and/or stochastic processes in early successional communities to a predominance of competition later on.

Microbial fuel cells have been proposed as possible alternative method to monitor organic content and other parameters of wastewaters. However, still rare, and short in-field experimentations were completed. In this work, long-term tests with two types of microbial fuel cells (planar and tubular geometry), equipped with carbon electrodes differently enriched and doped (enriched with carbon Nanotube, Ce-doped and/or undoped), were carried out in a wastewater plant (Bresso, Italy) aiming at the monitoring of the anoxic process in the tank. This experimentation aimed to improve experiences previously collected in different wastewater plants in Italy. Physico-chemical (temperature, light, redox potential) parameters were monitored during the MFCs’ operations. A hand-made automatic water sampler was used to perform some punctual chemical (COD, N, oxygen) measurements. The results indicated variable anoxic conditions in the monitored wastewater. The presence of a rich flora of protozoa on the anodes confirmed this condition. The MFCs signal was consequently very low during seasons of the year. Cathode and anode reversed, having different microbial activity on the anode and on the cathode. Next Generation Sequencing (NGS) of S16 RNA analysis gave insight on bacteria pools and the type of biofilm developing on different anodes and cathodes of MFCs.

ABSTRACTCryoconite holes are small depressions of the glacier surface filled with melting water and with a wind-blown debris on the bottom. These environments are considered hot spots of biodiversity and biological activities on glaciers and host communities dominated by bacteria. Most of the studies on cryoconite holes assume that their communities are stable. However, evidence of seasonal variation in cryoconite hole ecological communities exists. We investigated the variation of the bacterial communities of cryoconite holes of Forni Glacier (Central Italian Alps) during the melting seasons (July–September) 2013 and 2016, for which samples at three and five time-points, respectively were available. Bacterial communities were characterized by high-throughput Illumina sequencing of the hypervariable V5−V6 regions of 16S rRNA gene, while meteorological data were obtained by an automatic weather station. We found consistent trends in bacterial communities, which shifted from cyanobacteria-dominated communities in July to communities dominated by heterotrophic orders in late August and September. Temperature seems also to affect seasonal dynamics of communities. We also compared bacterial communities at the beginning of the melting season across 4 years (2012, 2013, 2015 and 2016) and found significant year-to-year variability. Cryoconite hole communities on temperate glaciers are therefore not temporally stable.

Microbial fuel cells (MFCs) are a rapidly growing technology for energy production from wastewater and biomasses. In a MFC, a microbial biofilm oxidizes organic matter and transfers electrons from reduced compounds to an anode as the electron acceptor by extracellular electron transfer (EET). The aim of this work was to characterize the microbial communities operating in a Single Chamber Microbial Fuel Cell (SCMFC) fed with acetate and inoculated with a biogas digestate in order to gain more insight into anodic and cathodic EET. Taxonomic characterization of the communities was carried out by Illumina sequencing of a fragment of the 16S rRNA gene. Microorganisms belonging to Geovibrio genus and purple non-sulfur (PNS) bacteria were found to be dominant in the anodic biofilm. The alkaliphilic genus Nitrincola and anaerobic microorganisms belonging to Porphyromonadaceae family were the most abundant bacteria in the cathodic biofilm.

Planar MFC prototypes were constructed and experimented to operate as sensors of the anoxic condition in a denitrification tank of a wastewater treatment plant in Italy, during different times in 2018 – 2019. Electrodes were differently enriched with carbon paint containing nanotubes and CeO2 nanoparticles. Performances of different electrodes were compared. Results underline critical anoxic conditions in the tank, that caused a very low signal and phenomena of signal reversion during some period of the year. the activity of aerobic microorganisms and protozoa growing and grazing the bacteria on the electrodes strongly influenced the signal of the MFCs. The presence of nanoceria enhanced, for some extent, the MFC signal, both in presence of reversing trends and in absence of these phenomena. In absence of reversing trends, nanoceria enhanced the MFC voltage. Such signal trends from MFCs can give, in real-time, useful information to optimize the purification process without the necessity of frequent biological and chemical analyses.

Abstract Produced water (PW) is the largest waste stream in the oil production process: it contains light polar and aliphatic hydrocarbons, production process compounds, dissolved gases, anions and cations. Disposal of PW is subjected to strict legislations. Oil producing countries are focused on finding effective and economic methods for its treatment. Some physical and chemical methods have been used for treatment of PW and biological treatments have been proven to efficiently remove dissolved hydrocarbon compounds. Coupling of anaerobic biological treatment with electrochemical technology in microbial fuel cells (MFCs) can in principle lead to the production of clean water and electric energy. The suitability of MFCs for improving the treatment of PW was investigated in the present work. For the first time, the simple design of single chamber MFCs fed with real PW (PW-MFCs) was studied, in different configurations: (i) with and without membrane; (ii) with and without Pt cathodic catalyst. The results demonstrate the effectiveness of the membraneless configuration without chemical catalyst at the cathode. Even though the electrical output of PW-MFCs was very low (3 mW m −2 ), it is currently the best reported performance. Furthermore, almost complete hydrocarbon degradation was achieved for each fed-cycle (96.6 ± 1.94%). The Coulombic efficiency was limited by the difficulty to obtain strict anaerobic condition at the anode, since the biocathode of PW-MFCs remained more permeable to oxygen than in acetate-fed MFCs. The DNA sequencing of operating anodic biofilm detected electroactive Desulfobulbaceae mixed to aerobic biodegraders ( Burkholderiales ) likely through cycling sulfur compounds, which enriched from the PW initial pool in the hypersaline environment. Above all, the results pointed to the practical possibility of using a MFC to enhance and monitor the PW biodegradation process. In fact, the MFC electrical output indicated the occurrence of anaerobic degradation, while the electrochemical parameters of cathode (Tafel slope) resulted correlated to aerobic degradation, suggesting the possibility to design an on-line sensor of the biotechnological industrial treatments of PW.

Electromethanogenesis is an innovative technology addressing the need of storing renewable energy from unprogrammable sources. It allows for the electrochemical production of methane from CO2-rich wastes on microbial cathodes, in a logic of power-to-gas (BEP2G). The challenge of cost-effective and sustainable biocathodes enhancing the microorganism performance and yield of electromethanogenesis is approached in this work. For the first time, porous carbonaceous cathodes were functionalized with Cu nanoparticles and hydroxyapatite (HAP) and successfully experimented for supporting microbial CO2 reduction reaction (CO2RR) to methane. Tests were performed in a double chamber system under CO2 flow at 45 ◦C. Next Generation Sequencing of 16S RNA indicated that the microbial pool on the cathodes was mostly enriched in Metanobacteriaceae (hydrogenotrophic Archaea) and different fermenting bacteria, depending on the cathode type. High methane production on cathodes made of Cu 20%, HAP 10%, and carbon balance (20Cu/10HAP) was achieved, with a maximum of 866 ± 199 mmol m− 2 d− 1 (projected cathode area, Coulombic efficiency of 64%), corresponding to values comparable to the maximum in literature, but in shorter timespans (8 vs. 30 days). The documented effect of pH stabilization in the cathodic chamber by HAP was one of the main parameters that concurred to the selectivity of CO2RR towards methane.