Fluorescence spectroscopy to monitor organic matter transformation during wet air oxidation of membrane-concentrated wastewater

Fluorescence spectroscopy was used to monitor organic matter removal during wet air oxidation of four types of membrane-concentrated industrial wastewaters. The overall process performance was assessed through chemical oxygen demand and total organic carbon. Fluorescence intensity exhibited distinct behaviors during wet air oxidation depending on the type of effluent: while some effluents showed a decrease in fluorescence intensities, landfill leachates and dairy wastewaters initially increased before declining. This indicates that heating can break down high-molecular-weight aggregates into smaller, more fluorescent molecules, especially in landfill leachates. The novelty of this study lies in combining fluorescence regional integration with multivariate data analysis to describe and predict global process parameters (chemical oxygen demand and total organic carbon) during wet air oxidation, enabling real-time assessment without using toxic reagents. Principal component analysis revealed that fluorescence responses differentiate samples by temperature and track the transformation of organic matter during oxidation experiments, showing decreases in fulvic and humic acid-like compounds and increases in microbial byproduct-like and aromatic protein-like materials. Partial Least Squares regression models provided satisfactory prediction of total organic carbon and chemical oxygen demand removals based solely on fluorescence intensity.