Investigation of Biologically Stable Biofilter Medium for Methane Mitigation by Methanotrophic Bacteria

Abstract

This study investigates the use of biologically stable materials including lava rock and biochar as alternative biofilter materials to common biodegradable materials such as compost. The results from batch studies indicate that lava rock and biochar can support the growth of methanotrophs for the oxidation of CH4 to CO2 with peak oxidation rates of more than 44 g (CH4)/h·m3 matrix. A statistical analysis of water content, media composition, and nitrogen determines that the level of nitrogen supplementation is the most important factor for CH4 oxidation. Nitrogen additions of up to 191 g (N)/m3 matrix maximize oxidation activity but concentrations above this value inhibit activity. The dominant methanotrophs belong to the genera Methylobacter and Methylomicrobium and maintain a steady relative abundance even as CH4 oxidation rates decrease. This indicates that the methanotrophs likely enter into a starvation phase (or a stationary phase of growth in which the population may cease to divide but remains metabolically active) in response to unfavorable nitrogen conditions, and their CH4 oxidation activities eventually recover as toxic NH3/NO3 intermediates are further oxidized during nitrogen metabolism.