Kinetics of Fluoxetine and Triclosan Oxidation during Municipal Wastewater Ozonation
Sustainable process-product development & green chemistry
Sustainable & Clean Technologies - Ib: Extraction & Remediation (T1-4b)
Keywords: triclosan, fluoxetine, ozone, hydroxyl radical, organic matter
Triclosan (TRI), 5-chloro-2-(2,4-dichlorophenoxy)phenol, is used as an antimicrobial agent in a large number of skin and oral care medical and household products (soaps, creams, toothpaste, mouthwash). The second considered compound, fluoxetine (N-methyl-8-14-(trifluoromethyl)phenoxylbenzenepropanamine), is an antidepressant drug, commercially sold as Prozac®. In comparison to traditional tri-cyclic antidepressants, fluoxetine (FLX) can be prescribed in lower doses with minimal side-effects, contributing in large part to its widespread use. Both compounds have been detected in wastewater at concentrations in the range of 0.4-1.3 µg/L. Although TRI and FLX concentrations appear to be significantly reduced during biological wastewater treatment (90%), residual concentrations detected in surface water may still be a matter of concern.
In the present work, reaction kinetics for the oxidation of TRI and FLX by aqueous ozone (O3) have been investigated. Second-order rate constants, kO3, were determined for reaction of O3 with each of TRI’s and FLX’s acid-base species. Although very high values of kO3 were measured for the deprotonated species of each target compound (kO3 = 5.1 (± 0.1) 108 M-1s-1 for anionic TRI and kO3 = 1.1 (± 0.1) 106 M-1s-1 for neutral FLX), only TRI was fast reacting at circumneutral pH (the pH-dependent, apparent second-order rate constants, kapp,O3 were 3.8 107 M-1s-1 for TRI and 9.6 102 M-1s-1 for FLX at pH 7). Kinetic modeling indicates that O3 reacts with TRI and FLX via electrophilic attack at their phenol and neutral amine moieties, respectively. TRI and FLX oxidation during ozonation of secondary effluent samples from two conventional activated sludge treatment plants were also investigated. TRI was oxidized with relatively high efficiency during wastewater ozonation, due to its high reactivity toward O3. Nearly 100% TRI depletion was achieved for a 4 mg/L O3 dose applied to a wastewater containing 7.5 mg/L of DOC, and ~58% TRI depletion for dosage of 6 mg/L O3 to a wastewater containing 12.4 mg/L of DOC. However, FLX transformation was less efficient, due to its low reactivity toward O3 at the circumneutral pH. Generally, the contributions of •OH to FLX oxidation were higher than for TRI, also primarily due to FLX’s lower reactivity toward O3. In any case, ozonation appears to provide an effective technique for enhancing the removal of TRI and FLX after biological treatment, with the objective of minimizing their discharge into the receiving surface waters.
Presented Wednesday 19, 15:20 to 15:40, in session Sustainable & Clean Technologies - Ib: Extraction-Remediation (T1-4b).
