Treatment of Combined Landfill Leachate and POME-Based Low-Cost Agricultural Waste

Landfill leachate, a highly contaminated liquid by-product of waste disposal, presents a major environmental challenge due to its complex mixture of persistent organic and inorganic pollutants, including humic substances, ammonia nitrogen, and heavy metals. This study investigates the use of palm oil mill effluent (POME), an agro-industrial waste rich in organic matter, as a low-cost, sustainable biological treatment medium for aged landfill leachate. A series of aeration experiments were conducted at various leachate-to-POME ratios (ranging from leachate only to equal volumes) under controlled conditions, with the aim of optimizing the removal efficiencies of chemical oxygen demand (COD), total suspended solids (TSS), color, and ammonia nitrogen (NH-N). Using response surface methodology and a face-centered central composite design, the optimal treatment conditions were identified as an addition of approximately 188 mL of POME per liter of leachate, coupled with an aeration time of 21 days. Under these optimal conditions, removal efficiencies reached 89.83% for COD, 66.1% for TSS, 55.19% for color, and 93.95% for NH-N. The biological aeration process was found to enhance microbial activity and facilitate ammonia stripping, significantly improving treatment outcomes. The study also assessed the removal of heavy metals, with removal efficiencies varying widely among metals, achieving up to 99% removal of cadmium and over 90% removal for iron, zinc, chromium, copper, cobalt, and lead. Manganese and arsenic showed lower removal rates but remained largely within regulatory limits. The presence of suspended solids and natural coagulants in POME likely contributed to metal removal via adsorption and sedimentation. Statistical analysis confirmed the robustness and adequacy of the developed models, with high coefficients of determination ( > 0.82) for the key response variables. Interaction effects between the leachate/POME ratio and aeration time were significant only for NH-N removal, highlighting synergistic effects enhancing ammonia volatilization. Although aeration significantly improved leachate quality, residual pollutant levels remained above permissible discharge limits, indicating the need for complementary treatment stages. Overall, this research demonstrates that POME, as a low-cost agricultural waste, can be effectively utilized in a biological aeration process to treat stabilized landfill leachate, offering a promising and sustainable approach for reducing organic pollutants and heavy metals in wastewater management.