Self-sensitized photodegradation of benzisothiazolinone by low-pressure UV-C irradiation: Kinetics, mechanisms, and the effect of media

Benzisothiazolinone (BIT) is a kind of non-oxidizing biocide widely used in reverse osmosis process for wastewater reclamation. Most BIT would reside in the RO (reverse osmosis) concentrates and show adverse effects on aquatic life when it is discharged into surface water. This study analyzed the photodegradation of BIT under UVC (254 nm) irradiation and found that UVC irradiation was as an efficient way to degrade BIT, of which the process could be well described by pseudo first order kinetics. As the results of BIT self-sensitization and light shield, the BIT photodegradation constant increased from 0.19 to 0.23 min−1 with increasing BIT concentration from 3 to 40 μM, and then followed by a decrease of the constant with further increasing BIT concentration. Radical species quenching experiments indicated that the photodegradation of BIT could be attributed to both direct and indirect photodegradation. Studies of the effects of pH suggested that non-charged state BIT (BIT0) in neutral and basic solution was much more photodegradable than protonated state BIT (BIT-H+) in acidic solution. The solution anion of HCO3− showed a slight promotion on BIT photodegradation. With the help of quadrupole time-of-flight mass spectrometry (QTOF-MS), the main intermediates of BIT photodegradation were identified. By employing the anion chromatography and HPLC tandem with triple quadrupole MS, the intermediates were quantified and the degradation pathway was proposed. This study could offer valuable suggestions for the efficient degradation of BIT and other similar emerging pollutants in wastewater reclamation and contribute to reclaimed water safety and sustainability.