Optimizing Electrocoagulation-Adsorption Treatment System for Comprehensive Water Quality Improvement in Olive-Mill-Wastewater (OMW): Synergy of EC Utilizing Al Electrodes and Olive Stones Biochar as a Sustainable Adsorbent

This research employed “Response Surface Methodology (RSM)” to assess the effectiveness of electrocoagulation (EC) in treating olive mill wastewater (OMW) before applying adsorption with olive stone biochar (OS) as a sustainable adsorbent. Several parameters, including reaction time, current density (CD), inter-electrode distance, and the number of electrodes, were optimized. Analysis using Minitab 22.2 resulted in robust regression models with high coefficients of determination (R2). The optimal parameters were CD of 12.41 mA/cm2, a time of 45.61 min, an inter-electrode spacing of 1 cm, and a maximum of 6 electrodes, resulting in an energy consumption (ENC) of 9.85 kWh/m3. Significant pollutant percentage removals were achieved: 72.32% for total Kjeldahl nitrogen (TKN), 80.74% for turbidity, 57.44% for total phenol (TPh), 56.9% for soluble chemical oxygen demand (CODsoluble), and 56.6% for total chemical oxygen demand (CODtotal). After the EC, the adsorption of pollutants was conducted using OS biochar that was generated through the pyrolysis of OS at a temperature of 500 °C. FTIR analysis of the biochar revealed key absorption bands that indicated the presence of inorganic compounds, aromatic C=C, and phenolic groups O-H. The integrated EC and adsorption (ECA) process demonstrated markedly higher efficiencies, with TPh removal reaching 61.41%, turbidity reduction at 81.92%, TKN reduction at 77.78%, CODsoluble reduction at 70.31%, CODtotal reduction at 65.1%, and project cost of $2.88/m3. The ECA process presents a promising treatment approach for OMW.