Comparison of methanotrophic activity at top and bottom layers in up-flow biofilters

The methane oxidation characteristics at the top and bottom layers in up-flow biofilters were investigated. Two biofilters were packed with perlite and tobermolite (biofilter A: respectively top and bottom; biofilter B: respectively bottom and top) and then compared. The methane oxidation rate was analyzed with the packed bed of the biofilter layers. The bacterial population in the biofilter was characterized using quantitative real-time PCR. For the methane oxidation rate of the biofilter A column, the perlite top part (845.16 ± 64.78 μmol·VS^-1·h^-1) gave a relatively higher value than the tobermolite bottom part (381.85 ± 42.00 μmol· VS^-1·h^-1). For the methane oxidation rate of the biofilter B column, the tobermolite top part (601.25 ± 37.78 μmol·VS^-1·h^-1) provided a relatively higher value than the perlite bottom part (411.07±53.02 μmol·VS^-1·h^-1). The pmoA gene copy numbers, responsible for methanotrophs, in the top layer of biofilter A (1.27E+13 pmoA gene copy number/mg-VSS) was higher than in the bottom layer (3.33E+13 pmoA gene copy number/mg-VSS). However, the population of methanotrophs in biofilter B was not significantly different between the top and bottom layers. These results suggest that although the methane oxidation rates of perlite and tobermolite in the top parts of biofilter A and B were high, methanotroph populations were higher in the bottom parts of both biofilters, with a rapid decline in methane concentrations within the biofilters.