Comparative study on packing materials for improved biological methanation in trickle Bed reactors

[Display omitted] •Packing materials could lay the foundation for commercial scaled-up TBRs.•Activated carbon higher surface area was the key to the successful biomethanation.•pH values and VFA concentrations are key indicators for biomethanation performance.•The metagenomics analysis explained the production of hexanoic and valeric acids.•Digestate from a biogas plant proved to be sufficient nutrient media supply. Packing materials improve biological methanation efficiency in Trickle Bed Reactors. The present study, which lies in the field of energy production and biotechnology, entailed the evaluation of commercial pelletized activated carbon and Raschig rings as packing materials. The evaluation focused on monitoring process indicators and examining the composition of the microbial community. Activated carbon resulted in enhanced methane purity, achieving a two-fold higher methane percentage than Raschig rings, maintaining a stable pH level within a range of 7–8 and reducing gas retention time from 6 h to 90 min. Additionally, the digestate derived from biogas plant was found to be a sufficient nutrient source for the process. Fermentative species with genes for β-oxidation, such as Amaricoccus sp. and Caloramator australicus could explain the production of hexanoic and valerate acids during reactor operation. Based on the physical properties of packing materials, the efficiency of biological methanation could be maximized.