Lime and Nano-Limestone Composite-Based Pretreatment and Adsorption Strategies for Olive Mill Wastewater Treatment: Toward Efficient and Sustainable Solutions

The treatment of olive mill wastewater (OMW) remains a major environmental challenge due to its high organic load and phenolic content. This study investigates a combined approach using lime pretreatment and limestone (LS)-based adsorption for cost-effective and sustainable OMW remediation. Locally sourced limestone was used in both micro- and nanoscale forms, while lime (CaO) was produced by calcination. The materials were characterized using X-ray Diffraction pattern (XRD), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET), and Point of Zero Charge (pHPZC) analyses to evaluate surface properties relevant to adsorption. Lime pretreatment achieved notable reductions in total suspended solids (TSS, 99%), chemical oxygen demand (COD, 43%), and total phenolic content (TPC, 48%). Subsequent adsorption with nano-limestone (particles obtained through high-energy ball milling, followed by sieving, with a size distribution 400–500 nm) further enhanced pollutant removal, achieving up to 72% COD and 89% TPC reduction in batch experiments. Column studies confirmed the synergistic effect of mixed particle sizes, yielding 65% COD and 76% TPC removal. The combined process demonstrates the potential of lime–limestone composites as locally available and eco-friendly materials for OMW treatment. While promising, the results represent laboratory-scale findings; further optimization and long-term assessments are recommended for field applications.