International Journal of Waste Resources

Abstract

Methanotrophic Oxygen Dependency and Availability for Sustained Oxidation

Abdulazize Alshareedah and P. Sallis

The oxidation of landfill methane is dependent upon a multitude of factors, some of which have been researched in-depth, while others require further investigation. One of the factors, that has not been carefully looked into, is the time factor for soils to rejuvenate and start oxidising methane efficiently. Using a batch reactor, soil samples, having no or little exposure to methane, were compared with other samples that had continuous methane exposure, in terms of the time they took to allow efficient methanotrophic mitigation of methane. In addition, the effect of oxygen availability and continuity to supply nourishment to the methanotrophic bacteria in relation to the soil types and the conditions of the soil's exposure to methane was also investigated. The results showed that acclimation time was an important factor in establishing high methane oxidation activity, with up to four days of lag time being observed before the methane oxidation could commence, as was the case for soil samples, previously exposed to methane. This is particularly important, since active land filling could last for twenty years of active operations, and would release up to an estimated 2.1 to 2.8 x 104 MtCO2-eq per day per landfill of methane into the atmosphere, globally, if the time lag were not controlled. Most importantly however, was the oxygen availability in landfill cover layers. The study showed that physical mixing of samples by mechanical agitation during incubation could allow higher concentrations of oxygen to permeate into the soil, increasing methane oxidation rates, which were approximately doubled due to this action. Furthermore, a linear relationship was found to form between methane consumption and the time when oxygen concentration was not rate limiting to the bacteria.