Mitigation of methane emission from Fakse landfill using a biowindow system.

Landfills are significant sources of atmospheric methane (CH(4)) that contributes to climate change, and therefore there is a need to reduce CH(4) emissions from landfills. A promising cost efficient technology is to integrate compost into landfill covers (so-called "biocovers") to enhance biological oxidation of CH(4). A full scale biocover system to reduce CH(4) emissions was installed at Fakse landfill, Denmark using composted yard waste as active material supporting CH(4) oxidation. Ten biowindows with a total area of 5000 m(2) were integrated into the existing cover at the 12 ha site. To increase CH(4) load to the biowindows, leachate wells were capped, and clay was added to slopes at the site. Point measurements using flux chambers suggested in most cases that almost all CH(4) was oxidized, but more detailed studies on emissions from the site after installation of the biocover as well as measurements of total CH(4) emissions showed that a significant portion of the emission quantified in the baseline study continued unabated from the site. Total emission measurements suggested a reduction in CH(4) emission of approximately 28% at the end of the one year monitoring period. This was supported by analysis of stable carbon isotopes which showed an increase in oxidation efficiency from 16% to 41%. The project documented that integrating approaches such a whole landfill emission measurements using tracer techniques or stable carbon isotope measurements of ambient air samples are needed to document CH(4) mitigation efficiencies of biocover systems. The study also revealed that there still exist several challenges to better optimize the functionality. The most important challenges are to control gas flow and evenly distribute the gas into the biocovers.