Sequential electrocoagulation–Fungal biotreatment as a pretreatment approach for olive mill wastewater (Fez, Morocco)

Abstract

The present study aims to evaluate a preliminary sequential treatment approach combining electrocoagulation (EC) and fungal bioremediation for the purification of olive mill wastewater (OMWW) diluted at a 1:10 ratio. EC, conducted with aluminum electrodes at a current density of 38 A·m⁻² for 4 h, achieved an initial reduction in chemical oxygen demand (COD) from 9520 to 4096 mg·L⁻¹ (56%) and in phenolic compounds (PC) from 0.55 to 0.28 g·L⁻¹ (49%). Subsequently, biological treatment with Aspergillus niger for 72 h further decreased COD to 2856 mg·L⁻¹ and PC to 0.137 g·L⁻¹, corresponding to cumulative removals of 70% and 75%, respectively. The treated effluent exhibited marked physicochemical improvements, including a decrease in turbidity to 15 NTU, a near-neutral pH (7.1), and a conductivity of 10.0 mS·cm⁻¹. The operational cost of the integrated EC–fungal process was estimated at 1.75 USD·m⁻³, with an associated carbon footprint of 3.4 kg CO₂·m⁻³. These values represent indicative laboratory-scale estimates, requiring validation at the pilot scale with a full accounting of electrode consumption, sludge management, and fungal biomass handling. Overall, the sequential EC–biotreatment constitutes a promising and sustainable pretreatment strategy for high-strength OMWW, facilitating subsequent polishing stages rather than serving as a stand-alone treatment solution.