Oxidation of β-blocker atenolol by a combination of UV light and chlorine: Kinetics, degradation pathways and toxicity assessment

Abstract

Degradation of atenolol (ATL) was achieved using combination of UV and chlorine treatment (UV/chlorine). Factors affecting ATL degradation, such as pH, chlorine dosage, common anions and natural organic matter (NOM), were systematically studied. ATL degradation could be described by the pseudo-first-order reaction kinetics. Combination of UV-254 nm and 100 μM of chlorine at pH 7 demonstrated 93.5% removal of 10 μM of ATL within 20 min. Radical scavenging tests indicated that both hydroxyl radicals (OH) and reactive chlorine species (RCS) participated in ATL degradation by UV/chlorine. The highest degradation rate was achieved at acidic pH. The contribution of RCS towards ATL degradation elevated as pH value increased. ATL degradation rate constant directly correlated with chlorine dosage in the 0–100 μM range. Scavenging effect of the excess chlorine occurred above 200 μM. HCO3− and NOM presence negatively affected ATL degradation, while Br− had a positive effect. Presence of Cl− had no noticeable impact on ATL degradation. Several ATL degradation pathways were proposed based on analysis of intermediate degradation products obtained using LC/MS/MS technique. Five typical disinfection byproducts including trichloromethane, dichloroacetaldehyde, trichloroacetonitrile, trichloroacetaldehyde and dichloroacetonitrile were detected. Although some intermediate products could potentially be more toxic than ATL, they were very likely further oxidized forming products with lower toxicity. In general, we demonstrated that UV/chlorine AOP is an effective approach to purify ATL contaminated water.