Comparative study of raw Pinus sylvestris sawdust and its activated carbon for chemical oxygen demand and polyphenols removal from Olive Mill Wastewater

This study investigates the treatment of Olive Mill Wastewater through adsorption using Raw Sawdust and Activated Carbon derived from Pinus sylvestris sawdust. Adsorption efficiency was evaluated by adjusting key parameters such as pH, adsorbent dose, contact time, temperature, particle size, and stirring speed. Adsorption experiments were performed using One-Factor-At-a-Time and Box-Behnken design to determine the optimal conditions for chemical oxygen demand (COD) and polyphenols removal. The experimental results revealed COD and polyphenols removal efficiencies of 47% and 74% under different conditions. RS was impregnated with H₃PO₄ (72%) and carbonized at 600 °C to produce AC, which resulted in 83.74% polyphenol and 61.15% COD removal under optimal conditions: pH 12, 0.62 g adsorbent, and 4 h contact time. The activation process greatly improved the adsorptive performance of raw sawdust, leading to a significant enhancement in adsorption capacities (Q_e). For chemical oxygen demand, the capacity increased from 400 mg/g with RS to 3145 mg/g with activated carbon, while for polyphenols, it improved from 38 mg/g to 250 mg/g. Desorption experiments yielded competitive recovery rates of 92% for COD and 24% for polyphenols. The adsorption mechanism was validated through isothermal and kinetic evaluation, showing that COD removal followed a pseudo-second-order model with monolayer adsorption described by the Langmuir isotherm. In contrast, polyphenol adsorption adhered to a pseudo-first-order model with multilayer adsorption described by the Freundlich isotherm. These findings highlight the superior efficiency of AC compared to RS, offering a sustainable and cost-effective solution for olive mill wastewater treatment.