Methane degradation

Because of its abundance in anoxic aquatic environments and its importance as a greenhouse gas, methane transformation by anaerobic oxidation has been the subject of numerous studies. The rates of anaerobic methane oxidation and the environments where it has been found were reviewed by Spormann and Widdel (2000). In marine systems, sulfate reduction has been shown to be an important part of the methane oxidation process. Landhlls, however, not hydrocarbon contaminations per se, are the main source of anthropogenic methane emissions in the US and, therefore, methane degradation processes are not discussed further in this chapter (see Chapter 9.16 for a discussion of methane generation from landfills). 

A metalimnion (the transitional layer between the epilimnion and the hypolim-nion) contains methanotrophic bacteria (bacteria that aerobically oxidize methane) at a cell concentration of 105 cells per milliliter. There is adequate oxygen available and the cells have a Vmax for CH4 of 10-19 mol/(cell sec) and a half saturation constant, Ks, of 10 4 mol/liter. At what rate, RCH<, is methane degraded if it is present at a concentration of 1.5 X 10-5 M ... 

Contrary to the results obtained by Lee et al. (2010), methane had an insignificant effect on benzene or toluene degradation in the study carried out by Lee et al. (2013). In this experiment landfill cover soil was used as an inoculum source to enrich a methane, benzene, and toluene-degrading consortium MBT14. The consortium was able to simultaneously degrade methane, benzene and toluene (Table 5.5). However, the coexistence of benzene and toluene inhibited the methane degradation rates. 

In one study, a coarse-grained sand aquifer was injected with methane and oxygen to stimulate the production of methane monooxygenase (MMO) enzyme which is capable of degrading TCE (18). TCE, added at 60—100 )-lg/L, was degraded by 20—30%. Injected concentrations of methane and oxygen were approximately 20 mg/L and 32 mg/L, respectively. 

When a plant was taken out of use, the cooling water lines were left full of water. Dismantling started nearly 20 years later. When a mechanic cut a cooling water line open with a torch, there was a small fire. Bacteria had degraded impurities in the water, forming hydrogen and methane [20]. 

Eng W, Palumbo AV, Sriharan S, et al. 1991. Methanol suppression of trichloroethylene degradation by Methylosinus trichosporium (OB3b) and methane-oxidizing mixed cultures. Appl Biochem Biotechnol 28/29 887-899. 

Sontoh S, JD Semrau (1998) Methane and trichloroethylene degradation by Methylosinus trichosporium OB3b expressing particulate methane monooxygenase. Appl Environ Microbiol 64 1106-1114. 

---