Application of electrochemical peroxidation with nanoscale zero-valent iron particles (nZVI) for selenium removal from oil refinery wastewater

This study uses the electrochemical peroxidation process to remove selenium in combination with nanoscale zero-valent iron particles (nZVI) as the iron source. Also, experiments with just the addition of the nZVI doses without current application were carried out. The nanoparticles were synthesized by the chemical reduction of iron chloride hexahydrate with sodium borohydride obtaining particles with an average size of 78 nm. The initial percentage of oxygen was in the range of 4.57% - 6.25% with no measurable increase after 15 days. 1 L of oil refinery wastewater was used in each experiment and the treatment time for all of them was 1 hour. The nZVI doses were: 950, 3800 and 11400 molFe/MolSe and the current density values were: 100 and 200 A/m2, all combinations were tested. The initial concentration of total Se in the wastewater was 0.16 mg/L. After the treatment, in the case of electrochemical peroxidation, a removal of 21.4 to 28.4% was achieved, depending on the nZVI dose and current density. In the case of treatment with just nZVI and no application of current, a removal of 54.1 to 94.5% was obtained, with the highest removal efficiency reached at a nanoparticle dose of 11400 molFe/MolSe.