The combination of ferrate(VI) and sulfite as a novel advanced oxidation process for enhanced degradation of organic contaminants

In this work, a novel advanced oxidation process (AOP) by the combination of ferrate (Fe(VI)) and sulfite for the treatment of recalcitrant contaminants was proposed and verified by experiments. The results showed that sulfite could significantly enhance the transformation of an emerging contaminant N,N-diethyl-3-toluamide (DEET) (a widely used insect repellent) by Fe(VI) (e.g., ∼78% of DEET lost within 10 s), whereas DEET showed negligible reactivity with Fe(VI) alone. Sulfate radical (SO4−) was demonstrated to be the primary active species in the Fe(VI)/sulfite system based on the radical scavenging experiments and electron paramagnetic resonance (EPR) experiments. The reaction pathway involving hydroxylation, de-alkylation, and alkylic-oxidation was proposed on the basis of the detected products. The degradation efficiency of DEET in the Fe(VI)/sulfite system was closely related to dosages of sulfite and Fe(VI), the initial concentration of DEET, and solution pH. The presence of humic acid (HA), Cl− and HCO3−/CO32− distinctly inhibited the transformation of DEET due to their quenching effect on SO4−. The effectiveness of DEET removal in real waters by a combined use of Fe(VI) and sulfite was also confirmed.