ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

The fate of tolfenamic acid in conventional chlorination and UV/chlorination process

Kheng Soo Tay and Nur Adawiyah Mansor

Department of Chemistry, Faculty of Science, Universiti Malaya, Kuala Lumpur, Malaysia

E-mail: khengsoo@um.edu.my

Received: 16 February 2022  Accepted: 14 July 2022

Abstract:

Tolfenamic acid (TOL) is a frequently detected non-steroidal anti-inflammatory painkiller in wastewater treatment plant effluents and the environment. Consequently, the fate of TOL in water treatment processes should be studied as some of the water treatment processes are known to produce toxic by-products. Chlorination is a widely used disinfection method, and UV/chlorination is an advanced oxidation process that has been frequently studied. This study investigated the kinetics and mechanism of TOL degradation by chlorination and UV/chlorination. The treatment of TOL by UV/chlorination has not been reported elsewhere. TOL reacted with the free available chlorine (FAC) during chlorination with the second-order rate constant of 1–41 M⁻¹ min⁻¹. The rate constants were decreased with increasing pH from 5 to 8 due to the reducing HOCl molar fraction. The TOL removal was largely improved by UV/chlorination. The reactive hydroxyl radical generated from the photolysis of FAC was the main species that improved the TOL removal. The removal of TOL by UV/chlorination can be enhanced by increasing the concentration of FAC. The efficiency of UV/chlorination in removing TOL was higher under acidic conditions due to the higher molar fraction of HOCl. For ecotoxicity study, TOL treatment with chlorination for 24 h produced non-toxic effluent. However, the toxicity of the TOL solution increased with prolonged exposure to UV/chlorination. Chlorinated TOL and 2-amino-5-chlorobenzoic acid were identified as the transformation by-products of TOL. The computational study predicted that chlorinated TOL is more toxic than TOL, and 2-amino-5-chlorobenzoic acid was less harmful than TOL.

Graphical abstract

Keywords: Toxic by-products; Pharmaceuticals; Water treatment; Disinfection; Non-steroidal anti-inflammatory

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-022-02378-8

Chemical Papers 76 (11) 6869–6877 (2022)