About This Project

We propose two approaches for developing a k-strategist microbiome reactor for removing dilute (<20 ppm) CH4 to sub-atmospheric levels – 1) a closed-circuit chemostat reactor and 2) a membrane biofilm reactor utilizing gas-permeable hollow fiber membranes. In designing and optimizing these reactors, a unique holistic microbiomic approach will be applied, leveraging high-affinity methanotrophs embedded within a network of natural microbiomes’ k-strategists and natural physicochemical matrix.

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Motivating Factor

CH₄ emissions have contributed ~30% of global warming to date [1], and natural sources may increase via feedback to warming [2]. Technologies for oxidizing atmospheric CH₄, area CH₄ emissions, and unavoidable point sources could substantially mitigate climate change. While CH₄ above ~4.4% can be flared, ~75% of CH₄ pollution is atmospheric (2 ppm) or too dilute to be oxidized at scale using existing technologies [3]. Methanotrophic bacteria express methane monooxygenases (MMO) to catalyze oxidation of CH₄ to methanol [4]. Recent observations indicate that ‘high-affinity’ methanotrophy can be catalyzed by a surprisingly diverse range of methanotrophs [5,6]. Oxidation of dilute CH₄ at scale may be possible using such methanotrophs, or even cell-free MMO in flow-through reactors. However, for practical dilute CH₄-removal system to achieve a net life-cycle CO₂eq reduction and economic viability, a reactor system that minimizes control efforts and energy/chemical input is essential [7].

Specific Bottleneck

Pure culture can be extremely costly to maintain in a reactor receiving inputs of elements (CH₄ and air) from its environment [8]. Additionally, energy or material inputs, if necessary to sustain reactor performance, will significantly impact the net CO₂eq balance – the CO₂eq associated with the inputs must remain lower than the CO₂eq removal. A holistic microbiomic approach, leveraging high-affinity methanotrophs embedded within a network of natural microbiomes’ k-strategists and a natural physicochemical matrix, may be the only avenue to achieving a self-sufficient reactor system. k-strategists are characterized by their slow growth and metabolism, and microbiomes consisting of k-strategists require minimal maintenance energy and are often found capable of recycling nutrients internally [9]. A reactor system utilizing such k-strategist microbiome has not yet been developed for any known environmental purpose, necessitating a de novo design and experimental validation.

Actionable Goals

Work should be carried out for 1) design, construction, and testing of CH₄ bioreactors that are optimized for low (<100 ppm) CH₄ concentration using a natural k-strategist microbiome; 2) mechanistic analyses of microbial CH₄ oxidation using multi-omics and mathematical modeling approach; and 3) design of scaled-up bioreactor for estimation of net CO₂eq-removal capability and cost-and-effect analysis.

Two unconventional reactor designs can be devised for accommodation of k-strategist CH₄-oxidizing microbiome, maintaining the physiocochemical and biological matrix within while facilitating CH₄ and O₂ mass transfer: 1) a closed-circuit chemostat with an gas equilibration chamber separate from the main reactor and 2) a membrane biofilm reactor featuring the new gas-permeable hollow fiber membrane, which allows diffusion of CH₄/O₂ through the membrane into the suspension. These reactors should be operable with the only input of dilute CH₄-containing air.