Enrichment of microbial consortium with hydrogenotrophic methanogens for the biological biogas upgrade to biomethane in a bubble reactor

The aim of the present study was to enrich a microbial consortium with hydrogenotrophic methanogens at mesophilic conditions by depleting the microorganisms that are not evolved in the biomethane production. For this purpose, a fed-batch bubble reactor was inoculated with biomass originating from a full-scale anaerobic bioreactor. The system was operated on a synthetic gas mixture of H2, CO2 and CH4, while a synthetic mineral medium was used as a nutrient source. To enhance the selection process, successive dilution cycles took place allowing the growth of the microorganisms involved in the process. The effect of the initial hydrogen concentration in each fed-batch cycle and the pH adjustment strategies were studied with the aim to enhance the metabolic pathway of hydrogenotrophic methanogenesis. To assess the impact of the operating conditions on the microbial community dynamics a cultivation-independent approach was applied. Different time points were chosen for 16S rDNA NGS (next generation sequencing) profiling in order to describe the relative abundance of phyla/genera of Bacteria and Archaea. Thanks to these molecular methods such as NGS, it is currently widely understood that microbial species might be very diverse depending on the conditions and the predominance of different phyla/genera can have significant impact on the stability and efficiency of the processes.