Permeabilidade ao ar e à água em misturas de solo e composto orgânico para uso em sistemas de cobertura de aterro sanitário.

Abstract

The final cover layer of a landfill works as environmental protection, which serves to reduce the water flow into the deposited solid waste and to minimize the greenhouse gases emissions to the atmosphere. It is noteworthy that air permeability studies in the cover layer of landfills are still incipient due to the difficulty of carrying out specific tests of the gas flow. Thus, this study aims to determine the air permeability of mixtures of soil and organic compost for use in the cover layer of landfills. Therefore, geotechnical characterization tests were carried out with five materials: the cover layer soil of the Landfill in Campina Grande-PB, the pure organic compost, and three mixtures of soil and organic compost in the proportions of 3:1, 1:1, and 1:3 by weight. In addition, with the five materials molded in optimum moisture, suction, water and air permeability tests were performed. Additional air permeability tests in the soil and compost mixtures were carried out according to a central composite design, varying the organic compost fraction, the saturation, and the compaction. After choosing the mixture that best fitted the cover layer and the methane oxidative layer, permeabilities predictions were calculated to analyze the water and airflow in the porous medium of the mixture. The results presented that the addition of organic compost to the soil changed its geotechnical properties, as increasing the granular fraction, the moisture retention capacity, the optimum moisture, the water and air permeability coefficient. On the other hand, the organic compost addition to the soil reduced the maximum dry density, specific gravity, and plasticity. The model from the central composite design presented that the organic compost fraction is the variable that most interferes in the air permeability of the soil and organic compost mixtures. The water retention curves presented that the presence of organic compost in the soil contributed to the reduction of air inlet suction value and the increase in the amount of water available to plants. When molded with optimum moisture, the mixtures 3:1 to 1:3 presented variations in intrinsic air permeability in the order of 10-15 to 10-14 m², and in water permeability in the order of 10-7 to 10-6 m.s-1. The mixture 3:1 was the most viable option for application in the cover layer of landfills, as it is the most suitable according to national and international parameters. This study collaborates for a better analysis of the requirements and properties to be considered in column tests in the laboratory and even to analyze criteria for design, execution, and maintenance of methane oxidative layer for use in landfills with similar climate and soil characteristics.