Pilot-Scale Demonstration of Virus Inactivation by the Sequential Chlorination Process

Abstract

The sequential chlorination process was developed by the Sanitation Districts of Los Angeles County (Districts) for disinfection of fully nitrified secondary effluent produced at the Districts' water reclamation plants. The process applies free chlorine and chloramines sequentially. Plantscale testing has shown that the process effectively inactivates bacteria while minimizing the formation of N-nitrosodimethylamine (NDMA) and trihalomethanes (THMs). Bench-scale experiments previously conducted by the Districts indicated that sequential chlorination can achieve regulatory targets for virus disinfection at much lower CT values. In this study, the Districts conducted pilot-scale experiments to verify the effectiveness of sequential chlorination against the surrogate virus MS2 coliphage, which was seeded into nitrified secondary effluent from the San Jose Creek West Water Reclamation Plant, and disinfected in pilot-scale chlorine contact channels. A total of 10 free chlorine experiments were conducted. All test conditions achieved at least 4.5 logs virus inactivation (lowest free chlorine residual CT value tested was 0.8 mg Cl 2 -min/L); 30 out of 34 test conditions achieved >5 logs inactivation. Five sequential chlorination experiments were conducted; free chlorine residual CT values ranged from 0.41 to 1.10 Cl 2 -min/L, and total chlorine residual CT values ranged from 80 and 122 mg Cl 2 -min/L. These experiments all achieved at least 5 logs inactivation of MS2 coliphage.

Sequential Chlorination for Recycled Water Disinfection: Advantages of Combining Free Chlorine and Chloramines

“…Experiments were performed with nitrified secondary effluent, both filtered and unfiltered, from the SJCEWRP and the San Jose Creek West WRP (SJCWWRP). This paper summarizes previously reported results on DBPs (Huitric et al, 2006;Huitric et al, 2007;Huitric et al, 2010) and on disinfection efficacy of poliovirus, MS2, and total coliform (Huitric et al, 2008;Huitric et al, 2010;Huitric et al, 2013) and demonstrates the advantages of using sequential chlorination (a multi-barrier disinfection method) over free chlorine or chloramines alone.…”

“…The results were published previously (Huitric et al, 2010), and are represented in Table 10 below. NDMA formation was calculated as the difference between the concentrations before and after disinfection and was the highest with chloramination, followed by sequential chlorination.…”

“…Results were previously presented (Huitric et al, 2010). The experimental conditions and MS2 inactivation results are summarized in Table 8.…”