Caracterização da fração fina de resíduos minerados visando uso geoambiental – estudo de caso de um aterro sanitário no Recôncavo da Bahia

Abstract

Landfill Mining (LFM) has emerged as a promising strategy for solid waste management by enabling resource recovery and contributing to the mitigation of environmental liabilities associated with landfills. Landfill-mined-soil-like-fraction (LFMSF) represents a significant portion of the excavated material and presents different possibilities for valorization. This research is based on the hypothesis that LFMSF can be used as a bio-cover material in landfills, provided that technical, environmental, and ecotoxicological criteria are met. The objectives of the study included analyzing the evolution of the LFM concept, evaluating the valorization potential of the mined fractions, investigating their contamination by Potentially Toxic Elements and the presence of microplastics, as well as examining their geotechnical behavior and ecotoxicological effects. To this end, a physical characterization of the waste was carried out using a representative 650 kg sample, in which LFMSF accounted for 32.8% and Refuse-Derived Fuel for 35.2%, on a dry basis. The high physical contamination observed in the latter category limits its direct application, requiring additional pre-treatment steps; in this context, the valorization of LFMSF as a covering material presents itself as a simpler and potentially more viable alternative. The dispersion of microplastics during the excavation of the mined waste was evaluated through spontaneous sedimentation collection, with the highest average number of particles observed at sampling point 4 (339 particles), attributed to the proximity of the excavation site to the oldest waste. It was found that the mobility of potentially toxic elements is not directly proportional to their total concentrations in the solid matrix of the LFMSF. In the solubilized extract, arsenic and manganese exhibited concentrations slightly above the limits established by ABNT NBR 10006, while cadmium in the leachate extract showed concentrations approximately tenfold higher than the reference value established by ABNT NBR 10005. In the ecotoxicological evaluation, using natural soil as a reference and the earthworm Eisenia andrei as a terrestrial test organism, lethality, avoidance, and reproduction tests were conducted, both in the solid matrix and in the elutriate from landfill-mined-soil-like-fractions (E-LFMSF) The absence of avoidance response to E-LFMSF suggests that the solubilized compounds did not negatively affect the earthworms, while the reproduction assays indicated impairment of the habitat function of LFMSF, evidenced by the reduction in the number of juveniles. Phytotoxicity was investigated using assays with seeds, employing E-LFMSF as the culture medium. The results indicated no effect on germination, while the root elongation of onion and arugula seeds showed a positive response; for tomato, low to moderate toxicity was observed. Finally, geotechnical tests demonstrated that the 1:1 mixture (soil:LFMSF) exhibited behavior compatible with its application as a bio-cover material, with water and air permeability values ​​similar to those of natural soil and water retention capacity close to that of LFMSF. The soil was classified as low-compressibility clay, while the mixture (1:1) and LFMSF were classified as clayey sand. In an integrated manner, the results indicate that LFMSF has potential for application as a bio-cover material in landfills, although it involves contamination risks that require careful management and further assessments. Further studies are suggested to evaluate field performance and long-term environmental safety.