Efficient treatment of saline recalcitrant petrochemical wastewater using heterogeneous UV-assisted sono-Fenton process.

An effective hybrid system was applied as a first report for successful treatment of recalcitrant petrochemical wastewater (PCW). In this regards, magnetic powdered activated carbon (MPAC), as a heterogeneous catalyst, was coupled with ultrasound (US) and UV irradiations for activation of HO (marked as MPAC/US/UV/HO). Chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including solution pH, MPAC and HO concentrations, US power and quenchers. A possible mechanism for catalytic degradation and generation of reactive species was proposed. To evaluate the biodegradability of both raw and treated PCWs, the activated sludge inhibition experiments were performed based on Zahn-Wellens test. MPAC indicated high catalytic activity, reusability and stability in the studied system. Over 87% of COD was removed under optimum conditions within 80 min treatment and the residual COD concentration reached 82.9 mg/L, which was permissible to discharge surface water sources based on the environmental standards. Leaching of transition metals from catalyst textural was negligible. Compared to homogeneous system (Fe/US/UV/HO), heterogeneous system (MPAC/US/UV/HO) represented a better performance in COD removal. Identification of intermediates by GC-MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. A biodegradability ratio of 64% and the residual COD of 28 mg/L for treated PCW, indicating that the biodegradability was improved and refractory organic matters removed effectively. As conclusion, MPAC/US/UV/HO hybrid system can be introduced as a successful advanced treatment process for efficient remediation of refractory PCWs.