Modelling microbial growth and biomass accumulation during methane oxidation in unsaturated soil

Abstract

Microbial aerobic methane oxidation (MAMO) affects methane emissions through landfill covers by not only consuming methane, but also causing biomass accumulation associated with bacterial growth. Although the reduction of soil porosity by biomass accumulation has been well recognized, most existing models ignore this effect when estimating MAMO efficiency. The present study proposes a newly improved theoretical model that could consider the effects of both microbial growth and biomass accumulation on MAMO during coupled water–gas–heat reactive transport in unsaturated soil. Comprehensive batch incubation tests were performed to determine the input parameters required. Part of a set of published experimental data was used to validate the new model, while the remainder of the dataset was used to evaluate the model predictability of soil–microbe interaction (i.e., class B prediction). When ambient temperature is relatively high (30 °C), ignoring biomass accumulation would lead to an overestimation of MAMO efficiency by more than three times. As the biomass accumulated in soil pores, the water permeability, gas permeability, and gas diffusion in the unsaturated soil reduced, consequently limiting the supply of oxygen to the bacteria for MAMO to take place.