Permeabilidade à água e ao lixiviado de misturas solo-bentonita em aterro sanitário.

Abstract

The base liners of sanitary landfills are of fundamental importance in the leachate containment process, this liquid fluid is the result of the degradation of landfill waste. Soil-bentonite liners are widely used and studied for the influence of the percolating fluid and the effects on its functionality regarding the vertical permeability of the layer. In this sense, the present study aimed to determine the hydraulic and microstructural behavior of soil-bentonite mixtures used in a sanitary landfill liner with water percolation and leachate. So, from a factorial design of the Central Composite Design (CCD) type, the variables of moisture content of compaction of the samples were evaluated at levels of 7, 11 and 15%, and of bentonite, at levels of 5, 15 and 25%, added to the natural soil. The fluids used on permeability tests were distilled water and leachate, generated at the Sanitary Landfill in Campina Grande-PB (SLCG). The leachate was subjected in the laboratory to physical-chemical, viscosity, and density characterization. The samples were tested in the Triflex-2 flexible wall permeameter, with methodologies suitable for the percolation of each fluid, with saturation using the percolating (leachate), obtaining the vertical permeability of the samples. In the results, it was observed that all samples present adequate water permeability to the standards for use in sanitary landfill liners. As for leachate permeability, it is possible to observe that, compared to water, the results are higher by up to two orders of magnitude. These experimental results showed the permeability of the soilbentonite mixtures, which is a behavior controlled by the liquid in the pores of the soil structure. Thus, these results of greater permeability were attributed to the increase in the ionic strength of the leached liquid in the voids of the soil, that is, to contaminating compounds and heavy metals in the leachate. Thus, these contaminants are attributed to the reduction of the Diffuse Double Layer (DDL), expansive potential, and flocculation of the clay which explains the different permeabilities depending on the fluid. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) images validated this analysis, showing a higher percentage of pores in soil samples percolated with leachate. Therefore, this study concludes that there is a change in the hydraulic and microstructural behavior of the bentonite-soil liners, showing the need to evaluate construction methodologies for these layers, with more adequate criteria than water permeability.