Impact of Nutrient Media and Temperature Shift on Methane Productivity and Carbon Monoxide Conversion in Syngas Biomethanation

Syngas biomethanation is an emerging technology which accelerates the utilization of gasification products. However, to upscale the process and reach technological maturity, the supply of nutrients is an important aspect to consider. This study aimed to evaluate the influence of three different nutrient media (defined basal medium, digestate and reject water) on CH4 productivity and CO conversion kinetics. Additionally, the feasibility of using a mesophilic inoculum for the transition to thermophilic conditions was assessed. The results show that the utilization of undefined nutrient media (digestate and reject water) is competitive with synthetic defined media concerning the kinetics of CH4 productivity and CO conversion. Still, nutrient-specific differences in the microbial composition were observed alongside a temperature-driven shift. Carbon monoxide was mainly converted to acetate, which was metabolized to H2 and CO2 by syntrophic acetate oxidizing bacteria (SAOB) and subsequently used for hydrogenotrophic methanogenesis. Non-defined nutrient media showed the same CH4 productivity and CO conversion as defined nutrient medium. Fast adaptation of mesophilic inoculum to thermophilic conditions achieved. Methanobacterium dominated the methanogenic community independent of temperature. Acetate was mainly converted by syntrophic acetate oxidizing bacteria. The CO-converting community differed with medium and temperature.