Response surface methodology optimization of COD removal from wastewater using peanut shell-derived activated carbons: a sustainable biosorption approach

Abstract

The contamination of water by industrial and urban waste discharge is a serious environmental problem, and the high chemical oxygen demand (COD) levels of the wastewater are detrimental to aquatic life due to oxygen depletion and ecological imbalance. This study presents a detailed investigation into the removal of COD from wastewater using peanut shell-derived activated carbons (PSACs) as green biosorbents, which were optimized using response surface methodology (RSM) with a central compositional design (CCD). Wastewater samples obtained from the Shahdara Drain in Delhi, India, were treated using the PSAC prepared via sulfuric acid activation and thermal carbonization at 550–650 °C. Three important operational parameters of the experiment were systematically tested: pH (3.32–6.68), contact time (46.36–113.64 min), and adsorbent dose (0.659–2.34 g L⁻¹) in a series of 20 experimental runs. Response surface analysis helped understand the intricate interactive behavior, and a pH of 6.0, a contact time of 74 min, and an adsorbent dose of 1.0 g L⁻¹ were the optimum operating conditions, with which the maximum COD removal was 87.8% and the adsorption capacity was 34.4 mg g⁻¹. Validation experiments proved the accuracy of prediction within the range of 5% error, demonstrating the strong model reliability. The near-neutral optimal pH, moderate contact time, and low dose of adsorbent contribute to the practical implementation in industrial applications. The current research confirms that peanut shell valorization is a sustainable and affordable method that utilizes wastewater to promote the principles of a circular economy, complies with the regulatory standards, and has high potential for large-scale industrial application.