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.