Effect of temperature on oxidation kinetics of testosterone and progestogens by ozone

Increasing presence of endocrine disrupting compounds (EDCs) in water sources and their adverse health effects on aquatic life are major concerns for water utilities and authorities worldwide. The oxidation kinetics for degradation of ozone resistant steroid hormones were investigated to quantify their removal in natural water under varying water temperatures and pH. Studying effect of temperature on oxidation of these compounds is one of the novel aspects of this research. The fate of four progestogens (progesterone, medroxyprogesetrone, levonorgestrel, and norethindrone) and, for the first time, of the androgenic steroid testosterone, in the presence of ozone was measured at bench scale in ultrapure water, natural surface water and wastewater. The estimated second order constant rate for testosterone of 590±0.13 M⁻¹s⁻¹ was comparable to our estimates and previous reports for similar structure progesterone (444-601 M⁻¹s⁻¹) and medroxyprogesterone (532±0.04 M⁻¹s⁻¹) and significantly lower than for levonorgestrel (2233 M⁻¹s⁻¹) and norethindrone (2292 M⁻¹s⁻¹). For all compounds the second-order rate constants increased from 3 folds for norethindrone to 5.5 folds for progesterone with temperatures ranging from 5 to 35 °C. The required activation energy was estimated for the five selected steroids and ranged from 30 Kj mol⁻¹ (norethindrone) to 39 Kj mol⁻¹ (progesterone). The removal rates of the selected compounds were predicted in natural water and wastewater. Finally, we showed that ozonation using typical disinfection dosages (Ct_O3= 2 mg min L⁻¹) were capable of removing 77% (progesterone) to 99% (levonorgestrel) at 21 °C and even less (47% medroxyprogesterone to 96% norethindrone) at 5 °C of the selected compounds.