For microbial community analysis, samples were collected from the initial inocula, biofilms formed on the packing materials, and liquid samples from the sump of the three TBRs. Biofilm samples were taken from three different heights within the reactors: top (6 cm), middle (24 cm), and bottom (42 cm). Sampling was conducted at two key time points when CO conversion rates were stable: in R1 and R2 on days 79 and 112, and in R3 on days 85 and 115.