<![CDATA[Growing plastic waste and industrial wastewater necessitate sustainable treatment solutions. This study optimized industrial wastewater treatment using activated carbon derived from high-density polyethylene (HDPE) pyrolysis char via thermal activation, eliminating the need for aggressive chemical agents. Characterization via FTIR, BET, and SEM-EDX revealed a micro-mesoporous structure with a BET surface area of 287.3 m²/g, a 90.05 atomic percent carbon content, and dominant pore sizes of 2.1 to 2.6 nm. The adsorbent performance was evaluated against laundry wastewater using a Central Composite Design and Response Surface Methodology. Statistical analysis yielded a robust model (R² = 0.9406, adequate precision = 15.54) to assess the impact of dosage, contact time, and initial concentration. Numerical optimization identified ideal conditions: 8.68 g/L dosage and 15-minute contact time for a 100 mg/L initial concentration. Experimental validation confirmed a 77.99% total dissolved solids (TDS) reduction, aligning closely with the predicted 79.48%. Post-treatment analysis indicated significant quality improvements, with COD and TOC levels decreasing to 35.8 mg/L and 21.6 mg/L, respectively, while dissolved oxygen increased from 0.6 to 4.3 mg/L. This research confirms that HDPE-derived activated carbon offers an effective, sustainable approach for both wastewater remediation and plastic waste valorization. Copyright © 2026 by Authors, Published by Universitas Diponegoro and BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).]]>
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