Numerical investigation of gas distribution layer (GDL) influence on methane removal efficiency in engineered methane oxidation biosystems (MOBs)

Methane (CH₄) emissions from landfills are a major source of greenhouse gases, particularly when traditional gas collection systems are no longer viable. Engineered methane oxidation biosystems (MOBs) offer a sustainable alternative by using microbial activity to convert CH₄ into carbon dioxide (CO₂). A critical yet often overlooked component of MOBs is the gas distribution layer (GDL), which facilitates lateral redistribution of CH₄ from point sources into the overlying methane oxidation layer (MOL). This study develops and validates a two-dimensional multicomponent reactive gas transport model in COMSOL Multiphysics to investigate how GDL thickness, width, intrinsic permeability, and its contrast with the MOL affect CH₄ distribution and removal efficiency. The model integrates Stefan-Maxwell diffusion, two-phase advective flow, and Monod kinetics for CH₄ oxidation. Validation against benchmark data confirmed its accuracy under both reactive and non-reactive conditions. One-dimensional simulations demonstrated that lower CH₄ flux enhances oxidation due to longer residence time and greater oxygen (O₂) availability. These insights were used to interpret simulations of a biowindow receiving point-source CH₄-CO₂ injection. Results show that even a 0.1 m GDL promotes lateral gas spreading and reduces peak CH₄ flux at the MOL base. Installation of a GDL increased CH₄ removal from 60 % to 91 % in a 4 m-wide MOB. Wider systems and high permeability contrast between GDL and MOL (R ≥ 10²) further enhanced flux uniformity. The study identifies a GDL permeability threshold (10^-10 m²) beyond which added benefit diminishes and confirms the GDL is a foundational design element for maximizing MOB efficiency.