Avaliação da utilização de mistura de solo e lodo de estação de tratamento de água como material de cobertura e de fundo em células experimentais de resíduos sólidos urbanos

Abstract

Sludge from water treatment plants (LETAs) are classified, according to NBR 10004 (ABNT, 2004), as solid waste and, therefore, must be reused or disposed of in an environmentally appropriate manner. In this research, LETA, soil and soil/sludge (SL) characterization were carried out, aiming to evaluate its use as cover and liner material in the landfill in Santa Maria, RS. Due to the permeability it was defined that the mixture of 15% of sludge with the soil was the most satisfactory. To evaluate the behavior of this mixture, two experimental cells (lysimeters) were constructed of reinforced concrete tubes, 1.5 m in diameter and 3 m high, each, making a volume of 4.20 m³, filled with solid urban waste previously characterized and then compressed. In one of the lysimeters (L1-SL15), a soil-sludge mixture was used as waterproofing in both cover and liner layers with a maximum dry density of 1235 Kg/m³; in the other lysimeter (L2) these layers were made using soil, with a maximum dry density of 1437 Kg/m³. These experimental cells were instrumented to measure the temperature, leachate, gases, settlements and the degradation processes over 677 days. In the samples collected from the interior of the lysimeters, the humidity of the residues in L1 (SL15) varied between 53% and 214% and the pH between 6.8 and 8, in L2 this variation of humidity was between 49% and 194% and pH between 4.6 and 7.5. The temperature inside the mass of waste was measured at depths of 50 cm, 130 cm and 218 cm and resulted in, respectively, average temperatures of 26ºC, 27.5ºC and 26ºC. The ambient temperature varied between 6°C and 35°C, with an average temperature of 22°C. The results of the analysis of the two lysimeters were compared with each other in order to assess whether the use of the sludge significantly altered the analyzed parameters. The measured settlements of the mass of waste, on average, were 271.5 mm in L1 (SL15) and 202 mm in L2. The settlement curves were modeled using eight settlement prediction models, and the models that presented the best fit were those of Bjarngard and Edgers (1990) and Gourc, Staub and Conte (2010). The settlements in L1 (SL15) were slightly higher than those measured in L2, however, statistically, there was no differentiation between the averages of settlements between them, with a probability of error of 5%. Among the drawn conclusions, there is evidence that the sludge did not cause changes in the chemical, physical and biological parameters of the leachate produced in L1 (SL15), so this evaluated mixture can be used as cover and liner material in landfills.