Application of tryptophan-like fluorescence index to quantify the trace organic compounds removal in wastewater ozonation.

The effectiveness of ozonation, one of the techniques known for destroying organic contaminants from wastewater, depends on the composition of the wastewater matrix. The required ozone (O) dose is determined based on the target compounds during ozonation. Hydroxyl radicals are quantified using a probe compound. The para-chlorobenzoic acid (pCBA) is typically used as a probe compound to measure hydroxyl radicals. However, real-time measurement is impossible, as the analysis process consumes time and resources. This study aimed to evaluate the spectroscopic characteristics of various organic substances in wastewater ozonation through fluorescence excitation-emission matrix and parallel factor analysis. The study also demonstrated that real-time analyzable tryptophan-like fluorescence (TLF) can be used as a hydroxyl radical index. Importantly, the correlation between para-chlorobenzoic acid and TLF was derived, and the results showed a high correlation (R = 0.91), confirming the reliability of our findings. Seven trace organic compounds, classified based on their reactivity with O and hydroxyl radicals, were selected as target compounds and treated with O. The TLF index was used as a model factor for the removal rate of the target compounds. The experimental and model values matched when the O dose was below 1.0 g O/g DOC (RMSE: 0.0445-0.0895).