Methane mitigation potential of industrial compost overs: Laboratory screening for use in landfill methane oxidation biosystems (MOBs)

Methane oxidation biosystems (MOBs) present a sustainable means to reduce methane (CH₄) emissions from landfills. MOBs typically utilize finished composts as a bio-active substrate to facilitate CH₄ oxidation. However, during industrial composting waste products are generated (termed compost overs) and may have suitable properties for MOBs; valorizing this waste stream. Using a structured screening approach, this study evaluated compost overs for use in MOBs to reduce emissions from landfills. Physicochemical characterization, batch testing, and long-term column injection experiments were conducted to compare compost overs with traditionally used finished compost. Physicochemical testing revealed the tested finished yard compost possessing more favorable intrinsic methanotrophic potential (e.g., CH₄ oxidation potential (MOP), respiration, and kinetic parameters) for effective CH₄ oxidation. In contrast, the tested compost overs showed structural properties such as coarser texture and higher air-filled porosity more favorable for gas transport and sustained oxidation under high loading rates. During flowing column experiments at moderate CH₄ loading (118 g m^-2 day^-1), both materials achieved complete removal; at elevated loading (236 g m^-2 day^-1), compost overs retained 80% efficiency while the finished compost dropped to 44%. These differences in efficiency were attributed to gas transport dynamics linked to material properties of the substrates. A new conceptual model is proposed for assessing the effectiveness of materials in MOBs including N₂ profiling to effectively diagnose oxidation dynamics. Results highlight that effective MOB design must integrate microbial kinetics with substrate structural and gas transport properties. Overall, compost overs could offer a robust, cost-effective material for use in MOBs.