Fluorescence sensor enabled control of contaminants of emerging concern in reclaimed wastewater using ozone-based treatment processes

Contaminants of emerging concern (CEC) pose significant challenges to environmental and human health. The development of the wastewater reuse sector, coupled with progressively stringent regulations, needs innovative systems that integrate advanced treatment processes with in-situ and real-time monitoring of CEC. This study investigates the use of a tryptophan-like fluorescence sensor for real-time and online monitoring of CEC within a pilot plant employing O₃-based advanced oxidation processes (AOPs). Two tertiary wastewater effluents (WW-1 and WW-2) were tested, placing the pilot system downstream of two different wastewater treatment plants (WWTPs). Priority substances and micropollutants detected in the investigated water matrixes such as pharmaceuticals, per- and polyfluoroalkyl substances (PFAS) were selected as targeted compounds in this study. Fluorescence degradation was detected in real-time by the sensor, showing a high capability to detect fast changes in water quality induced by oxidation. Furthermore, the real-time fluorescence showed better sensitivity than lab-scale fluorescence in detecting the fast action of hydroxyl radicals (·OH) during the O₃/H₂O₂ process, highlighting the importance of online monitoring. Selected CEC were degraded by AOPs with different percentages of removal efficiency (RE) (0%<RE<100% in WW-1 and 15%<RE<90% in WW-2) depending on oxidant doses and the reactivity of compounds with O₃ and ·OH. Fluorescence data by online sensor enabled accurate prediction of the removal of a wide spectrum of CEC during O₃ and O₃/H₂O₂ processes (R²≥0.93). Furthermore, real-time fluorescence data were successfully used to predict observed pseudo-first-order rate constants of CEC with O₃ or O₃/H₂O₂. Obtained results suggest that real-time fluorescence monitoring is an excellent tool to control CEC removal during O₃-based AOPs and monitor the transferred ozone in wastewater (R²≥0.94), contributing to the optimization of reagent dose, energy and costs.