This study presents a sustainable and cost-effective approach for treating olive mill wastewater (OMWW) using activated carbon derived from olive pomace, a major by-product of olive oil production. The proposed system integrates the production of this adsorbent with wastewater treatment in a two-stage, circular process that combines acid precipitation and adsorption. The prepared activated carbon exhibited a well-developed porous structure and high iodine value (948 mg/g), enabling efficient removal of phenolic compounds from OMWW. The results showed removal efficiencies exceeding 99% for phenolic compounds, along with significant reductions in key pollutants, including chemical oxygen demand and total organic carbon. It was hypothesized that integrating waste valorization with wastewater treatment can enhance both environmental and economic performance. The findings confirmed this hypothesis, demonstrating high treatment efficiency and substantial cost reduction through process optimization, including reduced adsorbent dosage and reuse. Process optimization, including reduced adsorbent dosage and reuse, led to a substantial decrease in treatment costs. Overall, this study demonstrated that integrating waste valorization with wastewater treatment offers an effective and practical solution for environmental management. The findings highlight the potential of olive pomace-derived activated carbon as a low-cost and sustainable adsorbent for large-scale applications.