Effect of microplastics on tertiary/quaternary treatment of urban wastewater: Fe-biochar/peroxymonosulfate/sunlight vs solar photo-Fenton

Microplastics (MPs) are detected at various stages of urban wastewater treatment plants (UWTPs), however their impact on tertiary/quaternary treatments has been underexplored so far. This study evaluates the effect of MPs on the degradation of four micropollutants (carbamazepine, diclofenac, sulfamethoxazole, and trimethoprim) and the inactivation of total and antibiotic resistant (AR) E. coli in secondary treated urban wastewater (SUWW) through two advanced oxidation processes: iron-modified biochar with peroxymonosulfate (Fe-BC/PMS) under sunlight and solar photo-Fenton (SPF) with iron-EDDS at circumneutral pH. Aqueous matrix effect was also investigated comparing the effect in tap water with SUWW. The presence of high concentration of MPs (1.0 g/L) in tap water sped up micropollutants degradation (80 % removal in 20 min) for Fe-BC/PMS/sunlight treatment in comparison to MP absence condition (80 % removal only after 60 min). On the contrary, micropollutants degradation efficiency by SPF treatment in tap water decreased by 27 % in presence of MPs (1.0 g/L). MPs did not significantly affect micropollutants removal in SUWW. Moreover, MPs presence reduced E. coli inactivation (both total and AR E. coli) efficiency (2.2 log units) by Fe-BC/PMS/sunlight treatment, which was attributed to the UV light scattering/blocking effect. Pilot scale results in a raceway pond photoreactor for simultaneous micropollutants removal and bacteria inactivation in SUWW showed 60 % higher micropollutants degradation for SPF with EDDS (103 kJ/m²). Whereas Fe-BC/PMS/sunlight treatment achieved complete inactivation of E. coli (<2 CFU/100 mL) in comparison to SPF with Fe:EDDS (0.5 log unit reduction) after 45 min treatment (103 kJ/m²).