For VFAs, a rapid consumption of VFAs was observed in R1, particularly with acetic acid. The VFA concentration peaked at 2.3 g L⁻¹ (with acetic acid at 1.7 g L⁻¹) on day 15. This was followed by a sharp decrease, reaching 0.5 g L⁻¹ for both total VFAs and acetic acid by day 43. After this point, VFA levels stabilized between 0.1 and 0.6 g L⁻¹ until the end of the experiment. This pattern corresponded closely with high CO conversion rates, suggesting that efficient microbial enrichment allowed rapid VFA consumption, especially acetic acid, may have contributed to enhanced reactor performance in R1.