Influence of nutrients on oxidation of low level methane by mixed methanotrophic consortia

Low-level methane emissions from coal mine ventilation air (CMV-CH₄; i.e., 1 % CH₄) can significantly contribute to global climate change, and therefore, treatment is important to reduce impacts. To investigate CMV-CH₄ abatement potential, five different mixed methanotrohic consortia (MMCs) were established from soil/sediment sources, i.e., landfill top cover soil, bio-solid compost, vegetated humus soil, estuarine and marine sediments. Enrichment conditions for MMCs were as follows: nitrate mineral salt (NMS) medium, pH ~ 6.8; 25 °C; 20–25 % CH₄; agitation 200 rpm; and culture period 20 days, in mini-bench-top bioreactors. The enriched cultures were supplemented with extra carbon (methanol 0.5–1.5 %, formate 5–15 mM, and acetate 5–15 mM), nitrogen (nitrate 0.5–1.5 g L⁻¹, ammonium 0.1–0.5 g L⁻¹, or urea: 0.1–0.5 g L⁻¹), and trace elements (copper 1–5 μM, iron 1–5 μM, and zinc 1–5 μM) in different batch experiments to improve low-level CH₄ abatement. Average CH₄ oxidation capacities (MOCs) of MMCs varied between 1.712 ± 0.032 and 1.963 ± 0.057 mg g⁻¹DW_biomass h⁻¹. Addition of formate improved the MOCs of MMCs, but the dose-response varied for different MMCs. Acetate, nitrate and copper had no significant effect on MOCs, while addition of methanol, ammonium, urea, iron and zinc impacted negatively. Overall, MMCs enriched from marine sediments and landfill top cover soil showed high MOCs which were largely resilient to nutrient supplementation, suggesting a strong potential for biofilter development for industrial low-level CH₄ abatement, such as those present in CMV.