Variability in excitation–emission spectra among wastewater treatment units and applications of fluorescence-based water quality monitoring

Abstract

ABSTRACT The study assessed the feasibility of fluorescence spectroscopy for characterizing the wastewater of functional wastewater treatment plants (WWTPs) as a real-time monitoring aspect. Peak picking and fluorescence regional integration (FRI) techniques are employed on 3D excitation–emission matrix (EEM) contours in understanding the variations of dissolved organic matter (DOM) of wastewater. Results demonstrate significant reductions in treated wastewater traits, including 94.38% of total suspended solids (TSS), 83.27% of dissolved organic carbon (DOC), and 85.38% of chemical oxygen demand (COD). The microbial analysis detected fecal and total coliforms in the effluent, highlighting the need for continuous monitoring and treatment. However, the biodegradable organic components decrease significantly, with protein-like peaks T1 and B1 intensities declining by 62.17 and 71.7%, respectively, during secondary treatment and further diminishing during tertiary treatment. Conversely, peaks associated with refractory humic and protein-bound components increased after tertiary treatment due to the formation of secondary products. The humification index (HIX) rises from influent to effluent, indicating a reduced carbon-to-nitrogen ratio. At the same time, the biological index (BIX) remained consistent, indicating microbial activity as a significant DOM contributor. The study establishes fluorescence spectroscopy as a promising and rapid monitoring tool for understanding DOM in WWTPs and optimizing treatment effectiveness.