Oxidation of methane in biotrickling filters inoculated with methanotrophic bacteria.

The oxidation of methane (CH4) using biofilters has been proposed as an alternative to mitigate anthropogenic greenhouse gas emissions with a low concentration of CH4 that cannot be used as a source of energy. However, conventional biofilters utilize organic packing materials that have a short lifespan, clogging problems, and are commonly inoculated with non-specific microorganisms leading to unpredictable CH4 elimination capacities (EC) and removal efficiencies (RE). The main objective of this work was to characterize the oxidation of CH4 in two biotrickling filters (BTFs) packed with polyethylene rings and inoculated with two methanotrophic bacteria, Methylomicrobium album and Methylocystis sp., in order to determine EC and CO2 production (pCO2) when using a specific inoculum. The repeatability of the results in both BTFs was determined when they operated at the same inlet load of CH4. A dynamic mathematical model that describes the CH4 abatement in the BTFs was developed and validated using mass transfer and kinetic parameters estimated independently. The results showed that EC and pCO2 of the BTFs are not identical but very similar for all the conditions tested. The use of specific inoculum has shown a faster startup and higher EC per unit area (0.019 gCH4 m-2 h-1) in comparison to most of the previous studies at the same CH4 load rate (23.2 gCH4 m-3 h-1). Global mass balance showed that the maximum reduction of CO2 equivalents was 98.5 gCO2eq m-3 h-1. The developed model satisfactorily described CH4 abatement in BTFs for a wide range of conditions.

Oxidation of methane by Methylomicrobium album and Methylocystis sp. in the presence of H2S and NH 3.

Oxidation of methane by methanotrophs, Methylomicrobium album and Methylocystis sp., was measured at several initial concentrations of H2S and NH3 in the headspace of stoppered flasks, at the same initial concentration of methane as sole carbon and energy source: 15 % (v/v). No effect was observed at 0.01 % (v/v) H2S and 0.025 % (v/v) NH3 in gas phase but over 0.05 and 0.025 % (v/v), respectively, they inhibited the oxidation of methane. The effect of H2S was stronger in Methylocystis sp. and both microorganisms were similarly affected by NH3. Depending on their concentrations in gas phase, H2S and NH3 can thus affect the rate of oxidation of methane and biomass growth of both methanotrophs.