Evolution of Absorbance Spectra of Ozonated Wastewater and Its Relationship with the Degradation of Trace-Level Organic Species

This study examined the evolution of absorbance spectra of wastewater ozonated using varying initial ozone concentrations or treatment times; concomitant changes of concentrations of trace-level pharmaceuticals were also quantified. The absorbance of ozonated wastewater decreased due to the degradation of chromophores in effluent organic matter (EfOM). The relative decrease of absorbance (Δ<i>A</i>/<i>A</i>₀) ranged from <30% for λ < 250 nm to >80% for λ > 320 nm. The removal of atenolol, carbamazepine, DEET, diclofenac, gemfibrozil, ibuprofen, iopromide, naproxen, propranolol, sulfamethoxazole, trimethoprim, and <i>p</i>-chlorobenzoic acid was strongly correlated with Δ<i>A</i>/<i>A</i>₀ values. The observed features were hypothesized to correspond to the engagement of kinetically distinct groups of EfOM chromophores. Modeling of the evolution of EfOM absorbance and concurrent degradation of trace-level organic species based on this hypothesis confirmed its applicability and utility for practical applications and theoretical exploration.