Utilização de bactérias na biorremediação: uma abordagem para redução da toxicidade de lixiviado de aterro sanitário de resíduos sólidos urbanos

Abstract

Efficient management of landfill leachates is essential for environmental sustainability due to the high toxicity and complexity of these effluents. This study investigated the efficacy of bioremediation as a strategy to reduce toxicity, using autochthonous bacteria isolated directly from the leachate at the Waste Treatment Center in Londrina, Paraná. Among the 12 bacterial strains isolated, strains B9 and B12 were selected for their high frequency in the samples and their distinct biochemical and morphotintorial potential. Strain B9, a Gram-positive bacterium, exhibited cocci morphology arranged in staphylococci, with the ability to ferment glucose, sucrose, and lactose, along with CO₂ production. Strain B12, a Gram-negative bacterium, showed bacilli morphology arranged in streptobacilli. The bioremediation experiments were conducted in Erlenmeyer flasks with different leachate concentrations (10%, 25%, 50%, and 100%), inoculated with 1.5 mL of the strains and incubated in a shaker at 140 rpm and 35 ± 1°C for 10 days. Physicochemical parameters such as Chemical Oxygen Demand (COD), lead and iron concentrations, pH, electrical conductivity, and dry cell mass were evaluated. The final results showed that, regarding heavy metals, the initial lead concentration was 0.0204 mg/L, which increased to 0.14 mg/L in the final control without inoculum but was reduced to 0.08 mg/L with strain B9 and 0.12 mg/L with strain B12. For iron, the initial concentration of 0.1 mg/L increased to 0.42 mg/L in the control without inoculum but was reduced to 0.15 mg/L with B9 and 0.39 mg/L with B12. This increase in metal concentrations in the control without inoculum is due to the mobilization and solubilization of metals in the leachate over time. However, the results highlight the ability of the selected strains to reduce contaminants, even with the increased leachate proportions. The dry cell mass in the 100% leachate experiment showed that strain B9 reached 0.26 g, while B12 registered 0.17 g. In the control without inoculum, the dry mass was only 0.1 g, demonstrating the strains' ability to survive and proliferate under adverse conditions. Despite the observed reductions in contamination parameters, the toxicity tests with Allium cepa did not show root growth in the treated samples, suggesting that although the strains reduced the pollutant load, the residual toxicity still hinders plant development. This indicates the need for process optimization and possible combination with other treatment techniques. In conclusion, this study reinforces the viability of bioremediation with autochthonous bacteria as an environmentally sustainable strategy for landfill leachate treatment, highlighting the importance of improving treatment conditions to maximize the effectiveness of the process.