Kinetics of microbial landfill methane oxidation in biofilters

A methane oxidizing biofilter system fitted to the passive venting system of a harbor sludge landfill in Germany was characterized with respect to the the methanotrophic population, methane oxidizing capacity, and reaction kinetics. Methanotrophic cell counts stabilized on a high level with 1.3x10(8) to 7.1x10(9) cells g dw(-1) about one year after first biofilter operation, and a maximum of 1.2x10(11) cells g dw(-1). Potential methane oxidizing activity varied between 5.3 and 10.7 mug h(-1) g dw(-1). Cell numbers correlated well with methane oxidation activities. Extrapolation of potential activities gave methane removal rates between 35 and 109 g CH4 h(-1) m(-3), calculated for 30degreesC. Optimum temperature was 38degreesC for freshly sampled biofilter material and 22degreesC for a methanotrophic enrichment culture grown at 10degreesC incubation temperature. Substrate kinetics revealed the presence of a low-affinity methane oxidizing community with a high V-max of 1.78 mumol CH4 h(-1) g ww(-1) and a high K-M of 15.1 muM. K-MO2 for methane oxidation was 58 muM. No substantial methane oxidizing activity was detected below 1.7-2.6 vol.-% O-2 in the gaseous phase. Methane deprivation led to a decrease in methane oxidation activity within 5-9 weeks but could still be detected after 25 weeks of substrate deprivation and was fully restored within 3 weeks of continuous methane supply. Very high salt loads are leached from the novel biofilter material, expanded clay, yielding electric conductivity values of up to 15 mS cm(-1) in the leachate. Values >6 mS cm(-1) were shown to depress methane consumption. Water retention characteristics of the material proved to be favourable for methane oxidizing systems with a gas permeable volume of 78% of bulk volume at field capacity water content. Correspondingly, no influence of water content oil methane oxidation activity could be detected at water contents between 2.5 and 20 vol.-%. (C) 2003 Elsevier Ltd. All rights reserved.