Several studies have shown the ex-situ biomethanation using biotrickling filter (BTF) as a feasible technology for PtM and for the biogas upgrading . The BTF is a 3 phase reactor where the HM are grown over a packing material as biofilm, the gaseous substrates (H 2 and CO 2 ) pass over the biofilm, and the liquid nutrient media is trickled over the packed bed to supply the nutrients. The solubility of H 2 is approx. 40 times lower than CO 2 and the overall process is mass transfer limited . The arrangement of HM over a packing material offers a relatively large surface area for the mass transfer of gaseous substrates that results in higher mass transfer rates. The main advantage of BTF is the relatively higher volumetric rate of CH 4 production as compared to the other biomethanation technologies. For example, CH 4 production rate of 15.4 Nm 3 /m 3 d was achieved using a lab scale BTF as compared to 3.7 Nm 3 /m 3 d using CSTR and 0.25 Nm 3 /m 3 d using upflow reactor .