<p>Landfill leachate poses significant environmental risks due to its high concentrations of heavy metals and harmful physicochemical properties, which threaten ecosystems and human health. This study investigates the use of powdered oyster mushrooms (<i>Pleurotus ostreatus</i>) as a sustainable bioremediation agent for treating landfill leachate. The mushrooms were cultivated on three agricultural waste substrates, sawdust, corncob, and coconut fiber, and their efficiency in heavy metal removal was evaluated through batch adsorption experiments. The pH, biosorbent dosage, and contact time were systematically optimized. Heavy metal concentrations (Cu, Mn, Cd, Pb, and Hg) were measured using atomic absorption spectrophotometry (AAS-Schimadzu model AA-6650 flame system) after acid digestion of the samples. Statistical analysis using ANOVA highlighted relationships between treatment parameters and removal efficiency. The results demonstrated removal efficiencies of 79.33% for Cu, 83.71% for Mn, 68.89% for Cd, 67.11% for Pb, and 83.25% for Hg under optimal conditions (pH 4 for Cu and Mn, pH 5 for Cd, pH 6 for Pb and Hg, adsorbent dosage of 2&#xa0;g, and contact time of 12&#xa0;h). Coconut fiber performed best for Cd, Pb, and Hg, while sawdust achieved the highest removal for Cu and Mn. However, treatment increased salinity, electrical conductivity, turbidity, and total dissolved solids in the leachate, indicating organic and inorganic release from the mushrooms. This study highlights the potential of powdered mushrooms as an affordable and eco-friendly solution for landfill leachate treatment. This approach promotes sustainability and supports a circular economy by utilizing agricultural waste as growth substrates.</p>