Tobermolite effects on methane removal activity and microbial community of a lab-scale soil biocover

Three identical lab-scale biocovers were packed with an engineered soil (BC 1), tobermolite only (BC 2), and a mixture of the soil and tobermolite (BC 3), and were operated at an inlet load of 338-400 g-CH₄ m^-2 d^-1 and a space velocity of 0.12 h^-1. The methane removal capacity was 293 ± 47 g-CH₄ m^-2 d^-1 in steady state in the BC 3, which was significantly higher than those in the BC 1 and BC 2 (106 ± 24 and 114 ± 48 g-CH₄ m^-2 d^-1, respectively). Quantitative PCR indicated that bacterial and methanotrophic densities (6.62-6.78 × 10⁷ 16S rDNA gene copy number g-dry sample^-1 and 1.37-2.23 × 10⁷ pmoA gene copy number g-dry sample^-1 in the BC 1 and BC 3, respectively) were significantly higher than those in the BC 2. Ribosomal tag pyrosequencing showed that methanotrophs comprised approximately 60 % of the bacterial community in the BC 2 and BC 3, while they only comprised 43 % in the BC 1. The engineered soil favored the growth of total bacteria including methanotrophs, while the presence of tobermolite enhanced the relative abundance of methanotrophs, resulting in an improved habitat for methanotrophs as well as greater methane mitigation performance in the mixture. Moreover, a batch experiment indicated that the soil and tobermolite mixture could display a stable methane oxidation level over wide temperature (20-40 °C, at least 38 μmol g-dry sample ^-1 h^-1) and pH (5-8, at least 61 μmol g-dry sample ^-1 h^-1) ranges. In conclusion, the soil and tobermolite mixture is promising for methane mitigation.