Replacing H2O2 with peroxymonosulfate challenges solar photo-Fenton for municipal wastewater reclamation through enhanced disinfection, antibiotic resistance mitigation, and organic microcontaminant removal.

This study comparatively assessed the replacement of hydrogen peroxide (H2O2) with peroxymonosulfate (HSO5-) in solar/iron/oxidant processes conducted in raceway pond reactors (RPR) under natural sunlight for the treatment of municipal wastewater treatment plant secondary effluents. The photo-Fenton (hv/Fe/H2O2) and its HSO5--based homologue (hv/Fe/HSO5-) processes were evaluated based on bactericidal potential, organic microcontaminant (OMC) removal, mitigation of antibiotic resistance spread, and cost-effectiveness. Replacing H2O2 with HSO5- resulted in higher bacterial inactivation, OMC degradation, and antibiotic resistance genes (ARGs) reduction. hv/Fe/HSO5- at pH 3.0 with 0.1/1.47 mM of Fe/HSO5- was the only condition complying with the stringent standards of EU 2020/741 (class A) for Escherichia coli and Clostridium perfringens inactivation, the EU 2024/3019 directive (6 OMC removal), and significantly reduced Klebsiella spp., Staphylococcus aureus, and Enterococcus spp. without 24 h regrowth and 90 % OMC reduction ([OMC]0 = 38.3 ± 7.4 μg·L-1, for 174 compounds investigated). The 16S rRNA and two ARGs, intI1 and blaTEM, were reduced by 3.3, 5.5, and 1.6 Log Reduction Value (LRV), respectively. If H2O2 replacement is contemplated, some key considerations are as follows: (i) E. coli inactivation was unaffected by acquired antibiotic resistance for either hv/Fe/H2O2 and hv/Fe/HSO5- processes; (ii) only hv/Fe/HSO5- processes effectively reduced the three monitored genes, regardless of the pH; and (iii) for equivalent targets, the economic efficiencies of both hv/Fe/H2O2 and hv/Fe/HSO5- were comparable for bacteria (1.21 - 2.66 LRV·€-1·m-2 respectively) and for OMC (12.6 - 10.6 mg·€-1·m-2 respectively).