Biogas Upgrading via Hydrogenotrophic Methanogenesis in Two-Stage Continuous Stirred Tank Reactors at Mesophilic and Thermophilic Conditions

摘要

This study proposes an innovative setup composed by two stage reactors to achieve biogas upgrading coupling the CO_2 in the biogas with external H_2 and subsequent conversion into CH_4 by hydrogenotrophic methanogenesis. In this configuration, the biogas produced in the first reactor was transferred to the second one, where H_2 was injected. This configuration was tested at both mesophilic and thermophilic conditions. After H_2 addition, the produced biogas was upgraded to average CH_4 content of 89% in the mesophilic reactor and 85% in the thermophilic. At thermophilic conditions, a higher efficiency of CH_4 production and CO_2 conversion was recorded. The consequent increase of pH did not inhibit the process indicating adaptation of microorganisms to higher pH levels. The effects of H_2 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 H_2 addition with Methanoculleus as dominant genus. The increase of hydrogenotrophic methanogens and syntrophic Desulfovibrio and the decrease of aceticlastic methanogens indicate a H_2-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.