Removal of methane from coal mine ventilation air by biofiltration

Abstract

Methane emitted by coal mine ventilation air (MVA) is a significant greenhouse gas. A mitigation strategy is the oxidation of methane to carbon dioxide, which is approximately twenty-one times less effective at global warming than methane on a mass-basis. The low non-combustible methane concentrations at high MVA flow rates call for a catalytic strategy of oxidation. A biofiltration technology was proposed as a promising solution to reduce/eliminate methane emissions from coal MVA. Unlike conventional CH4 removal technology, biofiltration is relatively cheap to build and operate as it works at ambient temperature and pressure. The challenge in developing biofilter system for MVA remains as high gas flow rate (> 50 m3 s-1) coupled with low methane concentrations (⠤ 1% (v/v) in air) require an improved biofilter performance to be applied for MVA applications. Several steps have been taken in this project including identification and isolation of methanotrophs (methane-oxidising microorganisms) from coal mine site which might be able to adapt better to MVA environments, investigation to seek optimum methane oxidation activity and microbial growth using pure culture of Methylosinus sporium (M. sporium) by batch experiments, and a lab-scale biofiltration study using inoculated (with M. sporium) and non-inoculated coal as packing material in a simulated MVA conditions. A laboratory-scale coal-packed biofilter was designed and partially removed methane from humidified air at flow rates between 0.2 and 2.4 L min-1. From the biofilter operation, the most abundant member of methane-oxidising microorganisms had been identified by 16S rRNA gene sequence as belonging to the methanotrophic genus Methylocystis. The greatest level of methane removal of 27.2 ± 0.66 gmethane m-3 empty bed h-1 was attained for the non-inoculated system, which was equivalent to removing 19.7 ± 2.9 % methane from an inlet concentration of 1% (v/v) at an inlet gas flow rate of 1.6 L min-1(2.4 min empty bed residence time). These results show that low-cost coal packing biofilter holds promising potential as a methane removal technology in MVA.