Development of heterogenous electro-Fenton process with immobilized FeWO4 catalyst for the degradation of tetracycline and the treatment of crude oil tank cleaning wastewater in neutral medium

The immobilization of FeWO4 nanoparticles was carried out utilizing polytetrafluoroethylene (PTFE) as adhesion agent and Na2SO4 as pore-forming agent, to develop a novel heterogenous electro-Fenton (HEF) process for the degradation of organic pollutants in neutral medium. The immobilized ferrous tungstate (FeWO4) catalyst exhibited a certain catalytic activity towards hydrogen peroxide (H2O2) activation generating active species (OH, O2– and 1O2), by which an effective tetracycline degradation was achieved under neutral condition. The low Fe-leaching amount indicated that the immobilized FeWO4 catalyst owns high chemical stability. Based on the above results, the HEF process was developed with one super-hydrophobic carbon cathode, one titanium-based oxide anode and the immobilized FeWO4 catalyst, which exhibited favorable ability for the degradation of organic pollutants attributed to the combined action of electro-Fenton oxidation and anodic oxidation. Under the optimum conditions, for the degradation of 40 mg L–1 tetracycline, the HEF process presented 100% tetracycline removal within 60 min. Furthermore, the treatment of crude oil tank cleaning wastewater by this oxidation process for 8 h presented the chemical oxygen demand (COD) removal of 85.0% and the total organic carbon (TOC) removal of 75.2%, whereas the other typical pollutants: ammonia nitrogen (NH4+-N) and volatile phenols were removed completely. After the treatment, the oil tank cleaning wastewater can be used as the recycled water or discharged into some surface waters directly. This work shows that the HEF process characterized by easy catalyst separation can not only effectively degrade organic pollutants but avoid the production of iron sludge and the inconvenience of pH adjustment.