Response Surface Methodology Optimization of COD Removal from Wastewater Using Peanut Shell-Derived Activated Carbon: A Sustainable Biosorption Approach

Abstract

Contamination of industrial and urban wastewater is a serious environmental problem, and its high chemical oxygen demand (COD) levels are detrimental to aquatic life due to oxygen loss and ecological imbalance. This study presents a detailed research on COD removal in wastewater using peanut shell-derived activated carbon (PSAC) as a green biosorbent that was optimized using the response surface methodology (RSM) with a central compositional design (CCD). Wastewater samples from the Shahdara Drain in Delhi, India, were treated using PSAC prepared via sulfuric acid activation and thermal carbonization at 550–650 oC. The experiment was systematically tested with three important operational parameters: 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 intricate interactive behavior, and the optimum operating conditions were pH 6.0, contact time 74 min, and adsorbent dose 1.0 g.L-1, with which the maximum COD removal was 87.8%, the adsorption capacity was 34.4 mg.g-1. Validation experiments of validation proved the accuracy of the prediction within the range of 5% error, which validates strong model reliability. The optimal pH was near-neutral, the moderate contact time, and a low dose of adsorbent, which contributes to the practical implementation in industrial applications. The current research confirms that peanut shell valorization is a sustainable and affordable method that uses wastewater to promote the principles of a circular economy and meets the standards of the regulatory framework, with high potential for large-scale industrial use.