Exploring the role of micronutrients in microbial communities during the biogas upgrading process

The increased concern regarding the greenhouse effect generated by the utilization of fossil fuels is pushing the development of sustainable energy alternatives. Biogas production has gained attention, due to the economic and functional benefits given by the conversion of organic waste into renewable energy. The key process that enables CO2 methanation through a complex microbiome is the Anaerobic Digestion (AD). Moreover, biological biogas upgrading (BBU) is a relevant technology applied with the aim to purify the final CH4 content to almost 95%. All the involved microbial species catalyze chemical reactions by various enzymes, and some of these contain cofactors where trace metals have a crucial role. The aim of this study was to investigate the effect of Nickel and Cobalt supplementation on the process efficiency and on the microbial composition and activity during the BBU. Analytical measurements revealed that Nickel increased the microbial community growth and its starvation resistance, while Cobalt enhanced CH4 production. Genome-centric metagenomics analysis revealed that, with a relative abundance of 90%, M. thermautotrophicus was the dominant hydrogenotrophic methanogen, while 10% of the microbial community belonged to bacteria. Additionally, genome-centric metatranscriptomic analysis shed light on the transcriptional activity of species involved in key routes of CO2 methanation and interspecies interactions.