Methane oxidation in water-spreading and compost biofilters

This study evaluated two biofilter designs to mitigate methane emissions from landfill vents. Water-spreading biofilters were designed to use the capillarity of coarse sand overlain by a finer sand to increase the active depth for methane oxidation. Compost biofilters consisted of 238-L barrels containing a 1: 1 mixture (by volume) of compost to expanded polystyrene pellets. Two replicates of each type of biofilter were tested at an outdoor facility. Gas inflow consisted of an approximately 1: 1 mixture (by volume) of CH4 and CO2. Methane output rates (J out; g m-2 day-1) were measured using the static chamber technique and the Pedersen et al. (2001) diffusion model. Methane oxidation rate (J ox; g m-2 day-1) and fraction of methane oxidized (f ox) were determined by mass balance. For methane inflow rates (J in) between 250 and 500 g m-2 day-1, the compost biofilter J ox, 242 g m-2 day-1, was not significantly different (P = 0.0647) than the water-spreading biofilter J ox, 203 g m-2 day-1; and the compost f ox, 69%, was not significantly different (P = 0.7354) than water-spreading f ox, 63%. The water-spreading biofilter was shown to generally perform as well as the compost biofilter, and it may be easier to implement at a landfill and require less maintenance.