This problem statement was submitted as part of a research funding application which was awarded by Spark.

Atmospheric methane oxidizing bacteria (atmMOB) comprise the biological sink for atmospheric methane, are widespread in soils, and have capacity to grow on hydrogen and CO in addition to methane from air, likely with N2 as a nitrogen source (Schmider 2024 , Tveit 2019). AtmMOB bioreactors are promising for atmospheric methane removal (He 2023), and can provide products from the resulting biomass, allowing for cost recovery for their manufacture and operation (Le 2023). While many bioreactor types can be used for atmospheric methane removal, solid-state bioreactors (SSBs), with their characteristically rapid gas-to-liquid mass transfer, offer major advantages with their simple design, high volumetric productivity, lower water demand, reduced energy costs, and ease of maintenance and operation (Krishania 2018 ; Fig. 1). Combining the ability of atmMOB to grow on 2 ppm methane with the high efficiency/low complexity of SSBs, this technology is attractive for atmospheric methane removal.

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Successful scale-up and deployment of SSBs to achieve a measurable impact on atmospheric methane requires the resolution of limitations in both the biology of the microbes and the manufacture/operation of SSBs. The main goals of this project are to: 1) define and optimize nutrient combinations for atmMOB that can thrive on dilute methane streams, 2) create a genome-scale metabolic (GSM) model of an atmMOB strain to better identify metabolic bottlenecks to improve methane uptake and growth, 3) operate lab-scale SSBs inoculated with control (Methylotuvimicrobium buryatense 5GB1) and atmMOB strains to characterize and enhance uptake and growth on dilute methane streams, and 4) test alternative hydrogel polymers as effective low-cost materials for SSBs. Through this approach, atmMOB strains will be characterized and optimized for growth on low methane streams and the feasibility of low-cost atmMOB SSBs for scale-up and deployment for atmospheric methane removal will be demonstrated.

This project will define and alleviate metabolic limitations of atmMOB through optimizing strains and creating feeding strategies on SSB platforms. SSBs are desirable for atmospheric methane removal due to their excellent gas-to-liquid mass transfer, low cost of static operation, low energy requirements, and recyclable polymer scaffolds, in contrast to liquid-phase systems that require constant supervision, maintenance, and high energy/operational costs (Krishania 2018). The social cost of atmospheric methane is estimated at $2,000 per tonne and rising. Successful scale-up of atmMOB SSBs with a low-cost hydrogel polymer instead of polyethylene glycol dimethacrylate (PEG), could potentially remove methane at <$1000 per tonne based on data from M. buryatense 5GB1 with a calculated removal rate of ~650 tonnes methane over 300 days operation at 100,000-L scale (He 2023 , Nikiema 2009). AtmMOB SSBs have potential as a climate beneficial, economically effective, scalable and safe technology.