OICC Press Anthropogenic Pollution 2588-4646 10 1 2026 06 30 Experimental Study on the Treatment and Reduction of Trace Metals, VSS, and TSS in Leachate Using Integrated Anaerobic -Aerobic system 10.57647/AP.2026.1001.04 EN Sadegh Motaghed Department of Natural Resources and Environment, SR.C., Islamic Azad University, Tehran, Iran Amir Hessam Hassni Department of Natural Resources and Environment, SR.C., Islamic Azad University, Tehran, Iran Seyed Alireza Hajiseyed Mirzahosseini Department of Natural Resources and Environment, SR.C., Islamic Azad University, Tehran, Iran Masoud Monavari Department of Natural Resources and Environment, SR.C., Islamic Azad University, Tehran, Iran Nabi allah Mansouri Department of Natural Resources and Environment, SR.C., Islamic Azad University, Tehran, Iran Journal Article 2026 06 30 This study evaluates the performance of a combined Upflow Anaerobic Sludge Blanket (UASB) reactor and aerated lagoon system for treating leachate from the Aghajari landfill. A 500 L UASB reactor served as the primary treatment unit, followed by a 1000 L aerated lagoon for further purification. The system's efficiency was assessed by measuring the removal of chemical oxygen demand (COD), Trace  metals (Mn, Zn, Cu, Fe, Ni ), and pH stability. The UASB reactor showed robust performance with an average COD removal efficiency of 79%, peaking at 97% at an organic loading rate (OLR) of 12 kg/m³·d. However, at an OLR of 20 kg/m³·d, the aerated lagoon's COD removal efficiency decreased to 60%, indicating sensitivity to higher organic loads. The UASB reactor effectively removed Trace  metals (Mn, Zn, Cu, Fe, Ni )with efficiencies between 70% and 90%, while the aerated lagoon's performance was comparatively lower. The analysis of volatile suspended solids (VSS) showed a significant reduction due to biological solids' settling and compaction, with the highest VSS concentrations in the reactor's lower sections. The mixed sludge acted as an effective adsorbent for Trace metals, reducing their toxicity and solubility. In conclusion, the combined UASB-aerated lagoon system is an effective solution for Aghajari landfill leachate treatment.