Mitigation of methane emissions from three Danish landfills using different biocover systems

The establishment of biocover systems is an emerging methodology in reducing methane (CH₄) emissions from landfills. This study investigated the performance of three biocover systems with different designs (biowindow and passively and actively loaded biofilters) in mitigating CH₄ emissions from three landfills in Denmark. A series of field tests were carried out to evaluate the functionality of each system, and total CH₄ emissions from relevant landfill sections or the entire landfill were measured before and after biocover implementation. Surface CH₄ concentration screening and local CH₄ fluxes showed generally low emissions from the biowindow/biofilters (mostly < 5 g CH₄ m^-2 d^-1), although some hotspots were identified on two actively loaded biofilters. One passively loaded biofilter exhibited high CH₄ emissions, mainly due to gas overloading into the system. Gas concentration profiles measured at different locations suggested uneven gas distribution in the biofilters, and significant CH₄ oxidation occurred in both the gas distribution layer (when oxygen was fed into the system) and the CH₄ oxidation layer. High CH₄ oxidation efficiencies of above 95% were found in all systems except for one biofilter (55%). Whole-site emission measurements showed CH₄ reduction efficiencies between 29 and 72% after implementing biocover systems at the three landfills, suggesting that they were efficient in reducing CH₄ emissions. The most challenging task for the passively loaded biocover systems was to control gas flow and secure homogenous gas distribution, while for actively loaded biocovers, it might be more important to eliminate emission hotspots for better functionality.