Electrocatalytic activation of peroxomonosulfate (PMS) under aerobic condition for the remediation of oil sands process water: Insight into one-pot synergistic coupling of PMS electro-activation and heterogeneous electro-Fenton processes

Alkaline industrial effluents possess a different challenge during treatment by advanced oxidation processes due to the reduction in redox potential of hydroxyl radical ((OH)-O-center dot) in basic media. Herein, electrocatalytic peroxomonosulfate activation (EC-PMS), which synergistically couples an early-stage PMS electro-activation (E-PMS) with subsequent heterogeneous electro-Fenton oxidation (HEF) catalyzed by Fe-modified biochar (BC-Fe) was investigated for enhanced degradation and mineralization of organics in oil sands process water (OSPW). The EC-PMS was first studied for the degradation of surrogate naphthenic acids (NAs) (5-phenylvalveric acid, (PVA)) as a synthetic process water and complete degradation of 50 mg L-1 PVA solution was achieved within very short treatment time (0.5 h) with excellent mineralization (>70 % TOC removal) in 6 h. The efficiency of EC-PMS for PVA degradation was affected by the applied current density, PMS, and catalyst dosage. The organic degradation, electroparamagnetic resonance spectrometry, quenching and chemical probe experiments showed that sulfate radical (SO4 center dot-) generated by E-PMS was the dominant radical oxidant for the degradation of PVA, contributing over 93 %, whereas (OH)-O-center dot produced from BC-Fe decomposition of electrogenerated H2O2 in HEF was responsible for the mineralization of the organic solution at the later stage of the coupled process. The EC-PMS showed excellent reusability and was effective for the treatment of real OSPW, achieving complete degradation of real NAs in OSPW and relatively good mineralization of the water. Analysis of the EC-PMS treated OSPW did not simulate any response during the bioactivity assay test using a macrophage cell line, indicating the complete detoxification of the water.