Oxidation of Pharmaceuticals during Ozonation and Advanced Oxidation Processes

TLDR

The study investigates the oxidation of pharmaceuticals during conventional ozonation and advanced oxidation processes applied in drinking water treatment. The authors determined second‑order rate constants for ozone and hydroxyl radical reactions of nine pharmaceuticals in bench‑scale experiments and then validated these kinetics in ozonation of various natural waters. Five pharmaceuticals were fully oxidized by ozone (kO3 > 5 × 10⁴ M⁻¹ s⁻¹), hydroxyl radicals reacted 2–3 times faster than MTBE or atrazine (kOH = 3.3–9.8 × 10⁹ M⁻¹ s⁻¹), and the pure‑solution rate constants accurately predicted removal in natural waters, confirming ozonation and AOPs as effective for pharmaceutical removal.

Abstract

This study investigates the oxidation of pharmaceuticals during conventional ozonation and advanced oxidation processes (AOPs) applied in drinking water treatment. In a first step, second-order rate constants for the reactions of selected pharmaceuticals with ozone (kO3) and OH radicals (kOH) were determined in bench-scale experiments (in brackets apparent kO3 at pH 7 and T = 20 °C): bezafibrate (590 ± 50 M-1 s-1), carbamazepine (∼3 × 105 M-1 s-1), diazepam (0.75 ± 0.15 M-1 s-1), diclofenac (∼1 × 106 M-1 s-1), 17α-ethinylestradiol (∼3 × 106 M-1 s-1), ibuprofen (9.6 ± 1.0 M-1 s-1), iopromide (<0.8 M-1 s-1), sulfamethoxazole (∼2.5 × 106 M-1 s-1), and roxithromycin (∼7 × 104 M-1 s-1). For five of the pharmaceuticals the apparent kO3 at pH 7 was >5 × 104 M-1 s-1, indicating that these compounds are completely transformed during ozonation processes. Values for kOH ranged from 3.3 to 9.8 × 109 M-1 s-1. Compared to other important micropollutants such as MTBE and atrazine, the selected pharmaceuticals reacted about two to three times faster with OH radicals. In the second part of the study, oxidation kinetics of the selected pharmaceuticals were investigated in ozonation experiments performed in different natural waters. It could be shown that the second-order rate constants determined in pure aqueous solution could be applied to predict the behavior of pharmaceuticals dissolved in natural waters. Overall it can be concluded that ozonation and AOPs are promising processes for an efficient removal of pharmaceuticals in drinking waters.