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

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. [GRAPHICS] .

Automated summary

Tolfenamic acid is a commonly detected pharmaceutical in wastewater and the environment. Its fate in water treatment processes and the toxic by-products generated need to be studied. This research investigated the removal efficiency and toxicity of Tolfenamic acid by chlorination and UV/chlorination.