Temperature effects on syngas biomethanation performed in a trickle bed reactor

[Display omitted] •Syngas biomethanation was performed by enriched mixed microbial consortia.•Better trickle bed reactor performance at 60 °C compared to 37 °C.•Mesophilic conditions resulted in higher electron yields to volatile fatty acids.•Higher relative abundance of methanogens in the biofilm compared to the liquid.•Different microbial genera dominated the thermophilic and mesophilic reactor. Syngas, mainly consisting of CO, H2 and CO2, can be generated from the gasification of biomass and organic waste and constitutes an important energy and carbon source. However, its biological conversion is still challenging due to the low solubility and the toxic nature of its components. In this study, enriched mixed microbial consortia were inoculated in trickle bed reactors operated in continuous mode with the supply of artificial syngas (45% H2, 25% CO2, 20% CO and 10% N2) under mesophilic (37 °C) and thermophilic (60 °C) conditions. The results revealed a clear superiority of the thermophilic conditions exhibiting higher methane productivities, higher conversion efficiencies and lower yields of byproducts at all steady states tested compared to mesophilic temperature. The highest methane productivity achieved was 8.49 mmol∙lbed−1∙h−1. The microorganisms related to syngas biomethanation were investigated through metagenomic analysis of samples obtained from the inoculum, the liquid phase and the biofilm of the reactors. The continuous operation altered completely the dominant species in mesophilic conditions compared to the inoculum. Accumulation of volatile fatty acids (VFAs) under mesophilic conditions was attributed to the high relative abundance of the genus Sporomusa. A large quantity of acetogenic cell debris scavengers and potential acetogenic metabolism of the genus Thermincola could justify accumulation of VFAs under thermophilic conditions. Absence of aceticlastic methanogens in both reactors was also noticeable. The archaeal communities were enhanced in the biofilm compared to the liquid phase presenting a 6.2 fold and a 1.8 fold higher relative abundance at 37 °C and 60 °C, respectively.