Assessing the performance of farm soil-based and hybrid biofilters for methane abatement

Mitigating methane (CH₄) emissions using methanotrophs (methane-oxidizing bacteria, MOB), is a simple, energy efficient and cheap technology. The abundance and distribution of MOB in the environmental samples is critical for efficient removal of emitted CH₄ from any source. This study evaluated the performance of farm soils without and with cheap, easily accessible bulking materials as sustainable hybrid biofilter media. Soil-only biofilters removed up to 865 ± 19 g CH₄ m^-3 d^-1 with well-drained organic carbon-rich soils compared with 264 ± 14 g CH₄ m^-3 d^-1 for poorly drained soil. The removal efficiency decreased with increasing flow rate (0.16→0.24 L min^-1) and subsequent priming could not return soil biofilters to their previous removal rate.Hybrid biofilters using organic, carbon-rich soils and compost removed up to 2698 g CH₄ m^-3 d^-1 (flow rate 0.35 L min^-1). Increasing CH₄ flow rates also reduced their efficiency, but the hybrid biofilters with compost quickly regained most of their efficiency and removed up to 2262 g CH₄ m^-3 d^-1 (flow rate 0.3 L min^-1) after remixing of biofilter media. These results show that hybrid biofilters removed higher CH₄ than soil-only biofilters and were also more resilient. The MOB gene abundance results complement the CH₄ removal capacity of both soil-only and hybrid biofilter materials used. The more aerobic, carbon-rich soils had more abundant MOB than the poorly drained soil. The most porous hybrid biofilter with compost and more available nutrients to sustain bacterial growth and activity had the highest MOB abundance and removed the most CH₄.