Eficiência de biowindows para mitigação das emissões fugitivas de metano em aterros sanitários de regiões semiáridas.

Abstract

Passive Methane Oxidation Biosystems are based on the optimization of geotechnical conditions of landfill cover layers for the oxidation process and mitigation of methane emissions to occur and involve biowindow, biofilter and biocover. Studies of these systems in semi-arid regions are still incipient, especially in Brazil. Thus, the objective of this work is to investigate the efficiency of biowindows for mitigation of methane emissions in landfills in semi-arid regions. The study area was a landfill located in the Brazilian semi-arid region, and the methodology involved three steps. Initially, a baseline study of methane and carbon dioxide emissions was carried out in the cover layer of Cell 1 of the Landfill, to verify the locations of higher emissions (hotspots) of gases and targeting of areas for mitigation of methane emissions. In the laboratory, tests were carried out on geotechnical, physical and chemical characterizations, water and air permeability, and suction analyses of soil samples collected from the cover layer of the Landfill, organic compost, and mixtures of soil and organic compost, in the weight proportions of 3:1, 1:1, and 1:3. In the field, in the area defined by the base study, two biowindows were installed, Bio1, with an oxidation layer composed of soil and soilorganic-compost mixture, and Bio2, with an oxidation layer composed only of local soil. The results of the baseline study indicated that methane emissions ranged from 0 to 386.7 g.m-2 day1 , associated with a lower degree occurrence of compaction and high degrees of saturation and soil moisture at the point of the highest methane emission. The 3:1 mix met most of the criteria of national and international standards for landfill cover layers. There was high spatial variability in the mitigation area, with the base methane fluxes much higher for Bio1. The average methane oxidation efficiency for Bio1 was 85%, while for Bio2 it was 96%, and Bio1 showed good resilience in operation even after events of high methane base flows or higher accumulated rainfall volume. The methane oxidation zone for Bio1 occurred between the depths of 0.10m and 0.30m in the dry and rainy periods, and between 0.10 and 0.50m for Bio2 in the rainy period. The identification of the highest methane emissions through the baseline study led to the site in the roof layer being targeted for biowindow intervention. In addition, the efficiency of the biowindows was related to higher methane input fluxes and accumulated rainfall volume in the 3 days prior to the measurements, which was tested by statistical analyses. The efficiency of the biosystem can be explained by the oxidative capacity over the period monitored, associated with the suitability of the materials to geotechnical parameters, as well as adaptability to the conditions of the region studied.