Biogas recovery from urban waste landfill drastically reduces greenhouse gas emissions

Landfills are strong emitters of greenhouse gases (GHGs) and volatile organic compounds to the atmosphere, but little is known on the long-term budget of those emissions and how they are impacted by biogas extraction for energy production. We measured continuously CO2 and CH4 emissions of two different Italian landfills in 2014-2015 by using the eddy covariance micrometeorological technique. The two sites, Case Passerini (CP, Florence, Italy) and Masseria del Pozzo-Schiavi-Novambiente (MSN, Giugliano, Italy), have similar age but differed in terms of type of waste, biogas extraction, and maintenance. The results revealed that total biogas production at CP was 7.4 kg m-2 y-1 CH4 and 29.5 kg m-2 y-1 CO2 while at MSN was lower for CH4 (4.7 kg m-2 y-1) and higher for CO2 (40.9 kg m-2 y-1). However at CP, where biogas extraction is applied, emissions to the atmosphere in terms of CO2eq were four times lower than at MSN, where biogas is not extracted and is entirely vented. Moreover the CP recovered biogas generated electric energy for 5025 MWhe further avoiding external emissions. Only 4.3% of CH4 production was released to the atmosphere while the remaining part was converted to CO2 in combustion. This study demonstrates the potential of using the eddy covariance technique to measure emissions continuously at the entire landfill scale, precisely quantifying the benefit of biogas extraction in terms of avoided GHGs emissions.