Simultaneous bacterial inactivation and microcontaminant removal by solar photo-Fenton mediated by Fe-NTA in WWTP secondary effluents.

Simultaneous microorganism inactivation and organic microcontaminant removal in municipal wastewater treatment plant (WWTP) secondary effluents by the solar photo-Fenton process mediated by Fe-NTA is studied in depth. To achieve this objective, different key aspects were addressed: (i) the effect of initial Fe-NTA concentration at 1:1 molar ratio (0.10-0.30 mM) and HO concentration (1.47-5.88 mM), (ii) the effect of initial microorganism load (10 and 10 CFU/mL) and (iii) the impact of the disinfection target on treatment cost. The first stage of this work was carried out in simulated WWTP effluent spiked with 100 µg/L of imidacloprid (IMD) as model microcontaminant and inoculated with Escherichia coli (E. coli) K-12 as reference strain, in a pilot scale raceway pond reactor with 5-cm of liquid-depth. Secondly, the most cost-effective conditions were validated in actual WWTP effluent. The kinetic analysis revealed that increasing Fe-NTA concentration over 0.20 mM does not significantly reduce treatment time due to the limited effect caused on the volumetric rate photon absorption. Treatment cost is determined by the disinfection process, since IMD removal was always faster than E. coli inactivation. The most cost-effective strategy to achieve 10 CFU/100 mL of E. coli (Regulation EU 2020/741) was 0.20/4.41 mM Fe-NTA/HO, with a cost of 0.32 €/m. A less restrictive disinfection target, 100 CFU/100 mL, allowed reducing reactant concentration and cost, 0.10/1.47 mM Fe-NTA/HO and 0.15 €/m, respectively. In both cases, no regrowth at 24 h and more than 90% of IMD removal were observed.