Methanotrophy in Landfill Cover Soils

Microbial CH4 oxidation shows two types of kinetics. Soils exposed to ambient CH4 concentrations display high-affinity (Km = 22-37 |il/l), low-capacity (Vmax = 0.73.6 nmol/g dry weight/h) CH4 oxidation kinetics. In contrast, soils exposed to high CH4 mixing ratios show low-affinity (Km = 1290-20680 |il/l), high-capacity (Vmax = 2703690 nmol/g dry weight/h) CH4 oxidation kinetics (Bender and Conrad, 1992). These researchers found that CH4 mixing ratios of 100-1000 |il/l are required to increase the CH4 oxidizing activity of soils. Schnell and King (1995) found that this threshold is between 170 and 1000 (j,l/l. The CH4 concentrations prevalent in landfill cover soils (1-60%) are sufficiently high for induction of low-affinity, high-capacity CH4 oxidation. This is illustrated in Fig. 12.2, which shows the relationship between the CH4 mixing ratio in landfill cover soils, and Vmax values of samples taken from these soils (Czepiel et al.,

Oxic zone: CH4 oxidation

3500

3000

2000

1500

1000

3000

2000

1500

1000

10 20 30 40

Fig. 12.2. Vmax versus methane (CH4) mixing ratios in landfill cover soils. (From Czepiel et al., 1996a.)

10 20 30 40

Fig. 12.2. Vmax versus methane (CH4) mixing ratios in landfill cover soils. (From Czepiel et al., 1996a.)

1996a). Pure cultures of known methanotro-phic bacteria also show a low-affinity, high-capacity pattern. Indeed, Wise et al. (1999) and Stralis-Pavese et al. (2004) showed that a wide variety of methanotrophic bacteria are present in landfill cover soils. For these reasons, it is useful to consider some characteristics of methanotrophs.

0 0

Post a comment