Optimizing electro-oxidation for selective trace micropollutant removal and energy efficiency in secondary effluents

This study investigated the electro-oxidation (EO) of three priority micropollutants: carbamazepine (CBZ), diuron (DIU), and perfluorooctane sulfonate (PFOS), in secondary-treated wastewater using boron-doped diamond (BDD) anodes. Although BDD anodes generate strong, largely non-selective oxidants; however, their performance at environmentally relevant concentrations, across different classes of micropollutants and under realistic organic-matter loads remains insufficiently characterized, especially for fluorinated and other recalcitrant contaminants. The selected compounds represent persistent pollutants with contrasting physicochemical properties and regulatory relevance (EU 2024/3019), which requires ≥ 80% CBZ between raw wastewater and the treated effluent. A four-factor central composite design (current density 10.7-33.0 mA/cm², electrolysis time 14-56 min, COD 0.9-29 mg/L, influent concentration 0.3-8.7 µg/L; pH 7-8; flow 40 L/h) was used to quantify the influence of operating conditions on removal efficiency, energy demand and by-product formation. CBZ and DIU were efficiently removed under most conditions (> 98%), while PFOS elimination reached up to 93% under high-time/high-current regimes. At environmentally relevant influent levels (1-2 µg/L), removals of 92% (CBZ), 80% (DIU) and 41% (PFOS) were achieved with a moderate and conceivable energy demand (3.35 kWh/m³). Dissolved organic matter slightly reduced degradation rates but did not prevent effective pollutant targeting. Acute toxicity assays revealed a transient increase occurring alongside the formation of primary transformation products, followed by a decline at extended treatment durations, consistent with the progressive oxidation of toxic intermediates. Overall, the study provides a quantitative, multi-response evaluation of BDD EO under realistic wastewater conditions, clarifying operational limits, energy-performance trade-offs, and transformation-product dynamics relevant to its implementation as an advanced polishing step.