Bioremediation of Organic Compounds and Trace Metals from Landfill Leachate Using <i>Lactobacillus kefiri</i> Strains: A Sustainable Approach Based on Facultative Treatment

The sustainable management of water resources is increasingly recognized as a critical component of environmental conservation and socio-economic development. Among the most challenging aspects of wastewater treatment is the effective remediation of landfill leachate, a complex and highly polluted effluent characterized by high levels of organic matter, ammonia, turbidity, and heavy metals. This study investigates an integrated treatment approach that combines chemical coagulation using aluminum sulfate with a subsequent bioremediation step employing <em>Lactobacillus kefiri</em>, a lactic acid bacterium isolated from kefir grains. The coagulation process, optimized for maximum efficiency, resulted in the removal of 50% of chemical oxygen demand (COD), 26% of ammonia nitrogen (NH<sub>3</sub>-N), and 75% of turbidity. Concurrently, notable reductions in trace metals were achieved, with removal efficiencies of 23% for copper (Cu), 45% for nickel (Ni), 41% for chromium (Cr), 33% for lead (Pb), and 20% for arsenic (As). To further enhance the leachate quality, biological treatment was applied using <em>L. kefiri</em> at a 5% (v/v) inoculum concentration for 24 hours. This step significantly improved pollutant removal, achieving a 63% reduction in COD, a 67% removal of NH<sub>3</sub>-N, and a 90% reduction overall. Moreover, biosorption by <em>L. kefiri</em> contributed to enhanced trace metal elimination, with average removal efficiencies reaching 32% for Cu, 53% for Ni, 47% for Cr, 40% for Pb, and 35% for As. These findings underline the potential of a sequential coagulation–bioremediation system as a viable and environmentally friendly alternative for the treatment of landfill leachate. The synergistic effect of chemical and biological processes offers an effective solution for mitigating the environmental impact of landfill-derived pollutants. It contributes to the development of more sustainable waste management practices.