Effect of disinfection on the photoreactivity of effluent organic matter and photodegradation of organic contaminants

Chlorine, UV254, and ozone are three typical processes commonly used for wastewater disinfection, which could change the photoreactivity of dissolved organic matter (DOM) in effluents of wastewater treatment plants (WWTPs). The photoinduced reactive species (RS) from DOM, primarily including the excited triplet state of DOM ((DOM)-D-3*), singlet oxygen (O-1(2)), and hydroxyl radical ((OH)-O-center dot), play important roles in the attenuation of contaminants. However, the effect of disinfection processes on the photosensitized degradation of contaminants is poorly understood. This paper presents the first evidence that (DOM)-D-3*, O-1(2), and (OH)-O-center dot interaction with three typical contaminants (diphenhydramine, cimetidine, and N,N-diethyl-m-toluamide (DEET)) was largely impacted by DOM after disinfection. The results of electron spin resonance (ESR) spectrometry and laser flash photolysis (LFP) experiments demonstrated that the chlorination increased the formation rate of (DOM)-D-3* and O-1(2), while UV254 irradiation and ozonation decreased the formation rate of these RS. All these three disinfection processes promoted the photoproduction of (OH)-O-center dot and increased the photodegradation rate constants (k(obs)) of DEET by 26-361%. The k(obs) of diphenhydramine, cimetidine, and DEET correlated positively with the formation rate of (DOM)-D-3*, O-1(2), and (OH)-O-center dot, respectively. The bimolecular reaction rate constant of (DOM)-D-3* with diphenhydramine increased by ~41% after chlorination. These findings suggest that disinfection processes altered the photo generation of RS from DOM, which significantly impacts the fate of trace pollutants in aquatic environments.

Automated summary

This study investigates the impact of chlorine, UV254, and ozone disinfection processes on the photosensitized degradation of contaminants. The results show that disinfection processes significantly alter the formation rate of photoinduced reactive species (RS) from dissolved organic matter (DOM) and increase the photodegradation rate constants (k(obs)) of contaminants.