Environmental EngineeringIn recent years, there has been growing concern about the appearance of pharmaceuticals in surface water as their uses increase. Even though the toxicological effect of low concentrations of pharmaceuticals in drinking water is not yet fully understood, these compounds should be minimized to reduce the risk of unpredictable long term effects based on the precautionary principles. Therefore, ozonation and copper catalyzed Fenton and photo-Fenton are discussed to be potential methods for effective control of pharmaceuticals in this study. In order to establish a practical and mechanistic database for pharmaceutical compounds using these methods, the following issues were investigated in this study.
Firstly, the oxidative degradation of pharmaceutical compounds is demonstrated during ozonation of different water samples in Ulsan. Diclofenac, carbamazepine, bezafibrate, and ibuprofen were selected as surrogate pharmaceutical compounds, and ozonation experiments were performed using four different water samples; Surface water samples (Hoeya Dam and Sayeon Dam) are the source of drinking water production in Ulsan. In addition, raw water and water after filtration were collected from the treatment process of Hoeya drinking water plant. Diclofenac and carbamazepine which have high reactivity with molecular ozone showed higher removal efficiencies than bezafibrate and ibuprofen during ozonation. The addition of tert-butanol, a hydroxyl radical scavenger, increased the removal efficiencies of diclofenac and carbamazepine by increasing the ozone exposure. However, the oxidation of bezafibrate and ibuprofen was inhibited by the presence of tert-butanol due to the suppression of the exposure to hydroxyl radical. The elimination of the selected pharmaceuticals could be successfully predicted by the kinetic model base on the Rct concept. Depending on the experimental condition, Rct values were determined to be (1.54~3.32)×10-7 and (1.19~3.04)×10-7 for the Sayeon Dam and the Hoeya Dam waters, respectively. Relatively high Rct values indicate that the conversion of O3 into ˙OH is more pronounced for surface waters in Ulsan compared to other water sources. Furthermore, model prediction of 19 pharmaceutical compounds including diclofenac, carbamazepine, bezafibrate, and ibuprofen was conducted in investigated water samples with various concentrations of ozone dose.
Secondly, the degradation of diclofenac and carbamazepine by the copper-catalyzed Fenton and photo-Fenton systems was investigated with respect to several reaction parameters such as pH, scavenger and catalyst concentration. The removal rates of targeted pharmaceutical compounds by the Cu(II)/H2O2 system were found to be gradually increased with rising pH from 3 to 8, but decreased at more alkaline pH. The possible mechanism was discussed based on Fenton chemistry, and two factors are recommended to be attributable for. First, the reduction reaction of Cu(II) is accelerated by the H2O2 and Cu(II) complexation, which favors the reaction of HO2- with Cu(II). Second, oxidants produced by the Cu(II)/H2O2 system are likely shifted from •OH to Cu(III) as pH increases up to the alkaline region, and the oxidants responsible for the degradation of diclofenac and carbamazepine was not Cu(III) but •OH. On the other hand, the rate of pharmaceutical compounds removal by the Cu(II)/H2O2 system were monitored under UV irradiation, and a significant enhancement was observed in the degradation rates at a range of pH (3-10). It is believed that the decomposition of pharmaceuticals is leveled up because of the Cu(II) reduction by HO2• which is produced from H2O2 photolysis. The evidences was shown in the comparison of Cu(II) and H2O2 absorbance at λmax = 365 nm and measurement of Cu(I) conversion rates.ope
