Factors affecting the elimination capacity of a passive methane biofilter

Passive biofilters are used for controlling CH₄ emissions from different sources with the help of methanotrophic bacteria. The CH₄ elimination capacity of a biofilter can be affected by different factors, such as the structure and composition of the filter material and formation of bacterial exopolymeric saccharides (EPS). Recognising these factors and resolving their effect on the elimination capacity is important for efficient greenhouse gas emission control. Hence, we studied the evolution of the elimination capacity of a passive CH₄ biofilter containing soil as low-cost filter material. We aimed at identifying the factors affecting the elimination capacity and tested the effectiveness of a mechanical regeneration method for improving the operation efficiency. A laboratory-scale biofilter containing landfill soil was operated for 148 days. The CH₄ removal efficiency reached 70 % in the beginning of the operation (0–7 days), but stabilised at 25 % after 50 days. The filter bed was mixed and loosened twice during the operation. As a result, the glucose content of the soil representing the clogging agent secreted by bacteria (EPS) remained stable throughout the experiment (23 mg g_dw^-1) and O₂ penetrated deeper in the filter bed indicating improved gas diffusion. However, the CH₄ removal efficiency did not increase from 25–30 %. The reason for this remained unknown, but the results indicated that soil as filter material was able to maintain its elimination capacity despite the formation of EPS. Mixing was shown to be an effective and necessary method for improving the gas diffusion properties of the filter bed.