This study proposes an innovative setup composed by two stage reactors to achieve biogas upgrading coupling the CO2 in the biogas with external H2 and subsequent conversion into CH4 by hydrogenotrophic methanogenesis. In this configuration, the biogas produced in the first reactor was transferred to the second one, where H2 was injected. This configuration was tested at both mesophilic and thermophilic conditions. After H2 addition, the produced biogas was upgraded to average CH4 content of 89% in the mesophilic reactor and 85% in the thermophilic. At thermophilic conditions, a higher efficiency of CH4 production and CO2 conversion was recorded. The consequent increase of pH did not inhibit the process indicating adaptation of microorganisms to higher pH levels. The effects of H2 on the microbial community were studied using high-throughput Illumina random sequences and full-length 16S rRNA genes extracted from the total sequences. The relative abundance of archaeal community markedly increased upon H2 addition with Methanoculleus as dominant genus. The increase of hydrogenotrophic methanogens and syntrophic Desulfovibrio and the decrease of aceticlastic methanogens indicate a H2-mediated shift toward the hydrogenotrophic pathway enhancing biogas upgrading. Moreover, Thermoanaerobacteraceae were likely involved in syntrophic acetate oxidation with hydrogenotrophic methanogens in absence of aceticlastic methanogenesis.

Biological biogas upgrading coupling CO with external H to form biomethane opens new avenues for sustainable biofuel production. For developing this technology, efficient H to liquid transfer is fundamental. This study proposes an innovative setup for in-situ biogas upgrading converting the CO in the biogas into CH, via hydrogenotrophic methanogenesis. The setup consisted of a granular reactor connected to a separate chamber, where H was injected. Different packing materials (rashig rings and alumina ceramic sponge) were tested to increase gas-liquid mass transfer. This aspect was optimized by liquid and gas recirculation and chamber configuration. It was shown that by distributing H through a metallic diffuser followed by ceramic sponge in a separate chamber, having a volume of 25% of the reactor, and by applying a mild gas recirculation, CO content in the biogas dropped from 42 to 10% and the final biogas was upgraded from 58 to 82% CH content.

This research aimed to better characterize the biogas microbiome by means of high throughput metagenomic sequencing and to elucidate the core microbial consortium existing in biogas reactors independently from the operational conditions. Assembly of shotgun reads followed by an established binning strategy resulted in the highest, up to now, extraction of microbial genomes involved in biogas producing systems. From the 236 extracted genome bins, it was remarkably found that the vast majority of them could only be characterized at high taxonomic levels. This result confirms that the biogas microbiome is comprised by a consortium of unknown species. A comparative analysis between the genome bins of the current study and those extracted from a previous metagenomic assembly demonstrated a similar phylogenetic distribution of the main taxa. Finally, this analysis led to the identification of a subset of common microbes that could be considered as the core essential group in biogas production.

No abstract

The principal axes of variation in plant function include the economics spectrum and size variation, both of which are implicated in primary ecological strategies. However, it is unclear to what extent vegetative traits and primary strategies correlate with reproductive traits, particularly for seed production. Fifteen traits, including whole-plant, leaf and seed traits (mass, number, total mass of seeds, volume and variance), were measured for 371 species from a range of habitats in Italy. Classification of Grime’s competitor, stress-tolerator, ruderal (CSR) strategies was applied from leaf area, leaf dry matter content and specific leaf area data. Relationships between vegetative traits, CSR values and seed traits were determined using principal components analysis (PCA) and Pearson’s correlation coefficients. PCA1 was an axis of economics, significantly correlated (positively) with leaf carbon concentration and S-selection, and (negatively) with leaf nitrogen concentration, flowering period and R-selection, but not seed traits. PCA2 was a plant size axis, significantly positively correlated with canopy height, leaf mass, C-selection and to a lesser extent seed size traits and total mass of seeds. PCA3 was a specific seed size-seed output axis, correlated positively with seed mass and volume, and negatively with seed number and variance. The loading of seed production traits on a general plant size axis alongside C-selection demonstrates that seed production traits are integral to CSR strategies. However, the stronger contribution of seed traits to a specific axis of variability is suggestive of reproductive variability beyond the CSR strategy, as predicted by the twin-filter model