Occurrence of disinfectant by-products during the sequential disinfection process

Abstract

Sequential disinfection is considered a viable treatment option for the effective inactivation of pathogenic micro-organisms such as oocysts of protozoan parasites (e.g. Cryptosporidium parvum etc.) and spores of vegetative bacteria (e.g. Bacillus subtilis and Bacillus anthracis) that cannot be treated by the single-step application of chlorine-based disinfectants and for viruses (e.g. Adenovirus) that cannot be easily treated by the single-step application of UV irradiation. The aim of this research was to investigate the inactivation of B. subtilis spore and formation of disinfection by-products (DBPs) during sequential disinfection using a combination of chlorine dioxide and chlorine (ClO₂/HOCl) or UV and chlorine (UV/HOCl) sequential disinfection. B. subtilis spores have been widely used as an indicator micro-organism for C. parvum oocysts. Trihalomethanes (THMs) and haloacetic acids have been used as indicator for DBPs. This study evaluates the effect of operating parameters (e.g. chemical dose, contact time, organic matters, and pH) on the synergistic inactivation of B. subtilis spores and formation properties of DBPs. The synergistic effect of inactivation of B. subtilis spores and control of DBPs were shown when chlorine dioxide was used as the primary disinfectant and chlorine as the secondary disinfect. Almost no synergistic effect was observed when the UV irradiation treatment was followed by chlorine reaction. In contrast to ClO₂/HOCl sequential disinfection, THMs were increased when UV was used as the primary disinfectant and chlorine as the secondary disinfect. UV/HOCl sequential disinfection increased chlorine demand about 13.6%. This result might be attributed to the change of DOM structure by UV irradiation which might affect the chlorine demand, and resulted in increase of THMs formation in the UV/HOCl sequential disinfection.

Keywords:

• Sequential disinfection
• Disinfectant by-products(DBPs)
• Chlorine dioxide
• UV
• Chlorine

Acknowledgements

This subject is supported by Korea Ministry of Environment as “The Eco-Innovation project (Global-Top project, GT-SWS-11-02-005-3)” and Korea Institute of Construction Technology (KICT) as “Smart Water μ-Grid project(2013-0013)”.

Notes

Presented at The Fifth Desalination Workshop (IDW 2012), October 28–31, 2012, Jeju, Korea