Three Horizontal Flow Biofilm Reactors (HFBRs) were used to treat contaminated airstreams containing low concentrations of methane (CH4) at 10°C. The HFBRs were seeded with a highly enriched, mixed biomass culture capable of CH4 oxidation. During the trial, which lasted 177 days, average CH4 removal rates of up 47.9% were observed in the HFBRs. A series of perturbations was applied to the HFBRs during the trial, including a low temperature period when the temperature was reduced to between 1°C and 5°C, and a shutdown period lasting 14 days when the CH4 supply was turned off. Reduced CH4 removal rates were observed in response to perturbations, but the HFBRs recovered after normal conditions were restored. Temporal biofilm samples were taken for fingerptinting of 16S rRNA genes, which indicated slightly reduced diversity over the trial. Fluorescent in-situ. Hybridizations detected both Type I and Type II methanotrophs, although in dispersed, small clusters along the biofilm. Maximum potential methane oxidation potential assays were used to characterise biofilm from vertically-resolved zones of sheets in the HFBRs and indicated excellent potential of the HFBRs to biologically treat low concentrations of CH4 at 10°C.