Design and establishment of a biofilter for treatment of manure methane emissions

During the storage of livestock manure in tanks, anaerobic degradation of organic material results in the production and emission of CH₄. This study tested a biofilter designed for CH₄ oxidation as a potential technology for mitigating CH₄ emissions from covered manure storage tanks. A full-scale biofilter (400 m²) was built next to a pig manure tank (4.400 m³). Total yearly CH₄ emissions from the manure tank prior to the establishment of the biofilter varied between 2.1 and 21.1 kg h^-1. With a pump flow of ∼ 100 m³ h^-1, it was possible to collect 75 % of the produced gas from the headspace of the tent covered manure tank. The average biofilter CH₄ load for the first year was 4.6 kg CH₄ h^-1, and the total yearly load was 42 tons of CH₄. The biofilter was monitored for 1.5 years by measuring the collected gas, gas concentrations in the gas distribution layer and the temperature and moisture in the CH₄ oxidation layer. Gas concentrations in the gas distribution layer were similar to inlet gas concentrations, indicating efficient gas transportation and distribution in the biofilter, whilst biofilter surface CH₄ screenings revealed only a few localised emission hotspots. The annual average temperature in the biofilter was 49 °C and was related to the CH₄ load. When the CH₄ load to the biofilter was stable and above 2 kg CH₄ h^-1, the temperature in the oxidation layer was found to be around 57 °C or higher, indicating that CH₄ oxidation was occurring.