Identification of resistant pharmaceuticals in ozonation using QSAR modeling and their fate in electro-peroxone process

The abatements of 89 pharmaceuticals in secondary effluent by ozonation and the electro-peroxone (E-peroxone) process were investigated. Based on the results, a quantitative structure-activity relationship (QSAR) model was developed to explore relationship between chemical structure of pharmaceuticals and their oxidation rates by ozone. The orthogonal projection to latent structure (OPLS) method was used to identify relevant chemical descriptors of the pharmaceuticals, from large number of descriptors, for model development. The resulting QSAR model, based on 44 molecular descriptors related to the ozone reactivity of the pharmaceuticals, showed high goodness of fit(R2 = 0.963) and predictive power (Q2 = 0.84). After validation, the model was used to predict second-order rate constants of 491 pharmaceuticals of special concern ( $${k_{{{\rm{O}}_3}}}$$ ) including the 89 studied experimentally. The predicted $${k_{{{\rm{O}}_3}}}$$ values and experimentally determined pseudo-first order rate constants of the pharmaceuticals’ abatement during ozonation (kOZ) and the E-peroxone process (kEP) were then used to assess effects of switching from ozonation to the E-peroxone process on removal of these pharmaceuticals. The results indicate that the E-peroxone process could accelerate the abatement of pharmaceuticals with relatively low ozone reactivity ( $${k_{{{\rm{O}}_3}}} < \; \sim {10^2}{{\rm{M}}^{- 1}} \cdot {{\rm{s}}^{ - 1}}$$ ) than ozonation (3–10 min versus 5–20 min). The validated QSAR model predicted 66 pharmaceuticals to be highly O3-resistant. The developed QSAR model may be used to estimate the ozone reactivity of pharmaceuticals of diverse chemistry and thus predict their fate in ozone-based processes.