Sago wastewater poses a significant environmental concern due to its high organic load and nutrient content. This study evaluated the performance of a hybrid wastewater treatment system combining activated carbon and Pistia stratiotes for the treatment of sago-processing effluent. The hypothesis that integrating adsorption and phytoremediation processes would enhance pollutant removal compared to single-media systems was tested, with particular emphasis on identifying an optimal media composition. A laboratory-scale gravity-driven downflow filtration system was operated under batch conditions with a detention time of four days. Treatment variations included different ratios of activated carbon and Pistia stratiotes (100:0, 75:25, 50:50, 25:75, and 0:100), along with a control unit. The findings demonstrated substantial improvements in wastewater quality across all treatment configurations, with the 75:25 activated carbon to Pistia stratiotes ratio showing the highest overall performance. In this configuration, BOD₅ decreased from 56.1 mg/L to 8.7 mg/L, COD from 72.3 mg/L to 10.96 mg/L, and phosphate from 4.04 mg/L to 0.006 mg/L, while pH remained stable and close to neutral. These results confirm a strong synergistic interaction between adsorption processes driven by activated carbon and nutrient uptake and microbial activity associated with Pistia stratiotes. In contrast, plant-dominated systems exhibited lower efficiency and indications of reduced stability, including potential nutrient re-release. The study is limited by its short-term batch design, which does not capture long-term operational stability, seasonal variability, or continuous-flow behavior. Nevertheless, the system demonstrates strong practical potential as a low-cost and low-energy treatment option for decentralized wastewater management in small-scale sago-processing industries. The main contribution of this work lies in identifying a non-linear relationship between treatment composition and performance, indicating that an optimal balance between adsorption and phytoremediation yields superior results and provides a practical framework for hybrid wastewater treatment design.