Utilizing Olive Mill Solid Wastes from the Olive Oil Industry as a Robust Adsorbent for Methylene Blue Removal

Abstract Ensuring access to affordable water treatment systems is paramount, given the dire situation where millions are deprived of clean drinking water. Industrial wastewater discharge, tainted with hazardous substances, including dyes like methylene blue (MB) from the textile sector, further emphasizes the need for water treatment to produce safe drinking water. This study explores the potential of Olive Mill Solid Waste (OMSW), an abundant and cost-effective agricultural waste in Mediterranean regions, to yield high-quality activated carbon (AC) with zinc chloride (ZnCl 2 ) activation for MB adsorption. The activation process, carried out at a modest temperature of 500°C without the need for an inert atmosphere, resulted in AC with remarkable characteristics, boasting a substantial surface area of 1,184 cm 2 .g − 1 and a total pore volume of 0.824 cm 3 .g − 1 . Extensive characterization of the AC was carried out through diverse techniques; Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Diffractometry (XRD), Brunauer, Emmett and Teller (BET) analysis, Zeta potential, Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) spectroscopy. The adsorption performance of the prepared AC was thoroughly evaluated through a comprehensive examination of various factors, including initial dye concentration, contact time, adsorbent dosage, and solution pH. The pH of the solution had minimal influence on MB adsorption, the maximum removal was 95% which was under slightly acidic pH conditions (5.8) and with an adsorbent dose of 0.4 g.L − 1 for a 50 mg.L − 1 MB concentration. Equilibrium data pertaining to MB adsorption were subjected to fitting with different models, namely Langmuir, Freundlich, and Temkin. Notably, the Langmuir model exhibited the best fit, revealing a maximum monolayer adsorption capacity of 500 mg.g − 1 at 25°C, and the adsorption kinetics closely followed a pseudo-second order model. These experimental results underscore the promising potential of Olive Mill Solid Waste (OMSW) as an affordable adsorbent for MB, hinting at its applicability for a diverse array of pollutant removal scenarios.