Microbial community development during syngas methanation in a trickle bed reactor with various nutrient sources

Abstract

AbstractMicrobial community development within an anaerobic trickle bed reactor (TBR) during methanation of syngas (56% H2, 30% CO, 14% CO2) was investigated using three different nutrient media: defined nutrient medium (241 days), diluted digestate from a thermophilic co-digestion plant operating with food waste (200 days) and reject water from dewatered digested sewage sludge at a wastewater treatment plant (220 days). Different TBR operating periods showed slightly different performance that was not clearly linked to the nutrient medium, as all proved suitable for the methanation process. During operation, maximum syngas load was 5.33 L per L packed bed volume (pbv) & day and methane (CH4) production was 1.26 L CH4/Lpbv/d. Microbial community analysis with Illumina Miseq targeting 16S rDNA revealed high relative abundance (20–40%) of several potential syngas and acetate consumers within the generaSporomusa,Spirochaetaceae,RikenellaceaeandAcetobacteriumduring the process. These were the dominant taxa except in a period with high flow rate of digestate from the food waste plant. The dominant methanogen in all periods was a member of the genusMethanobacterium, whileMethanosarcinawas also observed in the carrier community. As in reactor effluent, the dominant bacterial genus in the carrier wasSporomusa. These results show that syngas methanation in TBR can proceed well with different nutrient sources, including undefined medium of different origins. Moreover, the dominant syngas community remained the same over time even when non-sterilised digestates were used as nutrient medium.Key points•Independent of nutrient source, syngas methanation above 1 L/Lpbv/D was achieved.•Methanobacterium and Sporomusa were dominant genera throughout the process.•Acetate conversion proceededviaboth methanogenesis and syntrophic acetate oxidation.Graphical abstract