Microcontaminants degradation in tertiary effluent by modified solar photo-Fenton process at neutral pH using organic iron complexes: Influence of the peroxide source and matrix composition

Abstract

Peroxymonosulfate (HSO5–) and persulfate (S2O82–), both sources of sulfate radicals (SO4*–), were evaluated for the first time in modified solar photo-Fenton using Fe-chelating agents (nitriloacetic acid (NTA), ethylene diaminetetraacetic acid (EDTA), ethylenediamine-N,N′-disuccinic acid (EDDS) and citrate (Cit)) in comparison with hydrogen peroxide (H2O2) to degrade benzophenone-3 (BP-3), fipronil (FIP) and propylparaben (PPB) (100 µg L–1 each) in municipal tertiary effluent. Increasing HSO5– concentrations from 1.5 to 5.9 mmol L–1 reached ≥ 96 % removal for all iron complexes, while treatment efficiencies for all tested S2O82– concentrations (1.5–5.9 mmol L–1) were limited to 20 % to 55 %. This difference can be attributed to a pH decrease in the HSO5– system. The influence of pH and matrix composition upon treatment performance were also assessed in the FeNTA/S2O82– system, which was more efficient at pH < 7.0 due to higher availability of soluble iron, and partial removal of bicarbonate and humic acids caused by acidification. Matrix composition significantly influenced the process as higher degradation rates were achieved after isolated or combined removals of chloride, bicarbonate and sulfate. The comparison between naproxen (a high electron density compound) degradation and that of BP-3, FIP, and PPB by SO4*– - based advanced oxidation processes (SR-AOPs) was used to evaluate the influence of target compound structures upon treatment performance. S2O82− and HSO5– were ineffective for treatment at pH 7.0. Thus, H2O2 was the best peroxide source for target compounds degradation at neutral pH as this is the natural pH of municipal tertiary effluent and results indicated that the assessment and choice for SR-AOPs should consider the chemical structure of target compounds.