Combining UV and Chlorination for Recycled Water Disinfection
Year Released: 2010
Funding Partners: Bureau of Reclamation, Los Angeles County Sanitation District
Total Investment: $465,000 (Cash: $165,000, In-Kind: $305,000)
Principal Investigator: Chi-Chung Tang, Ph.D., P.E., Sanitation Districts of Los Angeles County
Disinfection is essential for ensuring the safety and quality of recycled water. Combining disinfectants has recently attracted increasing attention, because of benefits such as disinfection of a wider range of pathogens, improved reliability through redundancy, reduced disinfection byproducts (DBPs), and potential cost savings.
Goals and Objectives
The project evaluates the combination of UV with either free chlorine or chloramines for disinfection of recycled water.
UV, free chlorine, and chloramines were studied in bench-scale batch experiments and continuous-flow pilot experiments. Chloramines were formed using two methods: adding ammonia before free chlorine (ammonia-chlorine process) or after free chlorine (chlorine-ammonia process). Full disinfectant doses were 100 mJ/cm2 for UV, 6 mg Cl2/L for free chlorine, and a CT of 450 mg-min/L for chloramines. Each disinfectant was tested alone at 33, 67, and 100% of full doses. The 33% UV dose was also tested in combination with the 67% dose of free chlorine or chloramines, and vice versa. Experiments evaluated disinfection efficacy, DBP formation, removal of microconstituents, and effects of water quality and disinfectant order. Disinfection benchmarks were >4-log MS2 inactivation, >5-log poliovirus inactivation, and final total coliform levels <2.2 CFU/100 mL.
Findings and Conclusions
The results from this project indicate that UV combined with chloramines can achieve median total coliform levels below 2 CFU/100 mL and 5-log poliovirus inactivation; the UV/chlorine-ammonia process also generally provided 5-log MS2 inactivation, but the UV/ammonia-chlorine process provided <4-log MS2 inactivation. Free chlorine was a more effective disinfectant than chloramines. Combined UV/free chlorine provided 5-log inactivation of poliovirus and MS2, and median total coliform levels below 2 CFU/100 mL in most of the bench- and pilot-scale experiments.