Dynamics of non-Controlled Emission of Biogas From Landfills

Landfills are important sources of CH₄ and CO₂ as well as other toxic gas components to the atmosphere. A significant amount of gases could be released to the surrounding environment as a "non-controlled" emission in a diffuse form. To understand the dynamics of non-controlled emission of biogas from landfills several soil gas and CO₂ efflux surveys were performed at Arico's landfill (Tenerife, Canary Islands). Estimated diffuse CO₂ emission for Arico's landfill (0.33 Km²) were 507 td^-1 (1998) and 131 td^-1 (2000), showing different spatial CO₂ efflux patterns that can be explained in terms of new waste disposal and covering materials as well as the action of the biogas extraction system. Secular variations of diffuse CO₂ efflux and meteorological and soil variables were measured hourly at one site in the center of the landfill for 11 months. Diffuse CO₂ efflux ranged from 9.9 to 433.3 gm^-2d^{-1} with a median value of 242.7 \pm 73.3 gm^{-2}d^-1. Diffuse CO₂ efflux showed a temporal behavior that could be divided in two different periods: (a) a quasi-stationary period with minor fluctuations due to the influence of meteorological and soil variables, and (b) a non-stationary period with changing CO₂ efflux level and major variations related to the preliminary tests on the biogas extraction system for Arico's landfill. Air and ground temperatures exhibit significant positive correlation with the observed CO₂ efflux. Peaks of maximum inverse correlation between barometric pressure and CO₂ efflux are found at semi-diurnal and diurnal frequencies. Wind speed and wind direction are cross-correlated with CO2 efflux by 12 hours. These results suggest that (i) minor fluctuations in the CO₂ efflux could be driven by meteorological variations (solar radiation cycles and local wind patterns), and (ii) sudden and major fluctuations in the CO₂ efflux cannot be explained sufficiently in terms of the observed meteorological and soil variables' fluctuations.