Real-time wastewater quality monitoring by fluorescence sensors: Validation for COD and CEC monitoring and implication for carbon footprint reduction

This study investigated the applicability of a protein-like fluorescence sensor for wastewater quality monitoring. Several wastewater matrices, including raw, primary, secondary and tertiary effluents from three different wastewater treatment plants were used. Furthermore, the sensor was tested for the monitoring of quaternary effluent in a pilot scale plant installed downstream of a water reuse facility. The pilot plant involved advanced oxidation processes (AOPs) and granular activated carbon (GAC) adsorption. Corrections on excitation/emission matrices (EEMs), including Inner Filter Effect (IFE) and scattering, showed no effect on linear correlation ($R^2=0.99$) between sensor measurement and either raw or corrected benchtop protein-like fluorescence data, suggesting that for this application the signal from the sensor might be interpreted without the need for further adjustments. Furthermore, the use of quenched, diluted and filtered samples did not affect such correlations. Overall, the fluorescence sensor showed a very high capability to monitor a wide range of wastewater matrices, including raw, primary, secondary, tertiary, and quaternary effluents, providing fast information on the efficiency of the processes. The protein-like fluorescence monitoring by the real-time sensor was validated online through 9 days of 24-hour continuous monitoring of tertiary wastewater effluents. The employed fluorescence sensor was validated for monitoring the removal of contaminants of emerging concern (CEC), including a wide range of pharmaceuticals, in different AOP systems (ozone and UV based). In view of the results reported in this study, possible environmental implications for the reduction of the carbon footprint have emerged: the use of fluorescence sensors may contribute to the optimization of processes and the reduction of secondary pollution.