Inactivation of Microbial Indicators by the Sequential Chlorination Process

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Although wastewater disinfection has historically been accomplished with a single method such as chloramination or UV, recent research has begun to evaluate the use of multiple disinfectants in a cost-effective way to maximize disinfection efficacy and minimize formation of byproducts. The Sanitation Districts of Los Angeles County have developed and patented a two-step process called "sequential chlorination," which uses free chlorine followed by chloramines to produce disinfected tertiary recycled water meeting California Title 22 regulations, and have obtained conditional approval to use the process at one of their water reclamation plants. The free chlorine in the first step of sequential chlorination reliably achieves the ≥5-log MS2 coliphage inactivation required for disinfected tertiary recycled water at CT values (product of free chlorine residual and modal contact time) much lower than the prescriptive standard. Free chlorine also inactivates total coliform and does not form N-nitrosodimethylamine. However, free chlorine alone, at low doses and short contact times, does not consistently meet the total coliform standards for disinfected tertiary recycled water. The chloramines used in the second step of sequential chlorination reduce total coliform levels to meet the standards, and help to stop trihalomethanes formation. Thus, the combination of free chlorine and chloramines in sequential chlorination provides effective disinfection of MS2 coliphage and total coliform to meet regulatory requirements for disinfected tertiary recycled water, while balancing the formation of disinfection byproducts.

Section: Figure 2 Schematic Diagram Of Cdph Approved Sequential Chlosupporting

confidence: 68%

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

Huitric¹,

Munakata²,

Tang³

et al. 2014

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“…MS2 coliphage is relatively resistant to chloramines (Shang et al, 2007;Cooper et al, 2000;Shin and Sobsey, 1998;Staub et al, 1995), therefore it is not a good indicator for virus inactivation by chloramines. At the range of TCRCT tested in the sequential chlorination experiments, previous laboratory experiment results, shown in Figure 6, suggested that chloramines would inactivate at least 1 log poliovirus (Huitric et al, 2008). Step 1 -Free Chlorine…”

Section: Sequential Chlorination Experimentsmentioning

confidence: 80%

“…Since sequential chlorination uses free chlorine, which is a stronger disinfectant than chloramines, it is expected that the process would achieve the 5-log virus inactivation required by Title 22 at CT values lower than 450 mg Cl 2 -min/L. This was demonstrated in bench-scale experiments using effluent samples from two water reclamation plants operated by the Districts (Huitric et al, 2008). In the current study, the Districts conducted pilot-scale experiments to demonstrate virus inactivation by the sequential chlorination process.…”

Section: Figure 2 Sequential Chlorination and Chlorine Residual Controlmentioning

confidence: 95%

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

Huitric¹,

Tang²,

Munakata³

et al. 2010

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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.

“…Chloramines minimize formation of trihalomethanes (THMs) and provide additional bacterial and viral inactivation. Plant-scale testing has shown that the process significantly reduces NDMA formation in comparison to chloramination, generates insignificant amounts of cyanide, and does not cause aquatic toxicity (Huitric et al, 2007, Huitric et al, 2008, Maguin et al, 2009. To obtain Title 22 approval for sequential chlorination, the Districts needed to demonstrate that the process can achieve >5-log virus inactivation when it is used to disinfect filtered effluent.…”

Section: Figure 1 -The Districts' Wastewater Treatment Facilitiesmentioning

confidence: 99%

Determining Free Chlorine Residual CT Values to Meet California Title 22 Five-log Virus Inactivation Requirement

Huitric¹,

Munakata²,

Tang³

et al. 2013

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The Sanitation Districts of Los Angeles County (Districts) have developed a two-step disinfection process called sequential chlorination. The process applies free chlorine and chloramines in sequence and effectively inactivates viral and bacterial target organisms while minimizing the formation of N-nitrosodimethylamine (NDMA) and trihalomethanes (THMs). To meet California Title 22 requirements as an alternative disinfection technology for "disinfected tertiary recycled water", the Districts embarked on this study and conducted experiments using a pilot-scale channel to determine the free chlorine residual CT values needed to achieve 5-log virus inactivation. Pulse tracer tests were first conducted to demonstrate that the pilot-scale results were applicable to the full-scale system. For the disinfection experiments, the target virus, MS2 coliphage, was seeded into filtered effluent produced from the San Jose Creek East Water Reclamation Plant (SJCEWRP). A total of 114 pilot-scale disinfection tests were conducted over a range of ammonia concentrations, turbidity levels, pH values, and water temperatures. Data from the 99 tests achieving breakpoint chlorination were analyzed and are presented in this paper. For the conditions tested (breakpoint chlorination, modal contact time >4 min), the lowest tested free chlorine residual CT (FCRCT) range of 2 to 3 mg-min/L achieved an average MS2 coliphage inactivation of 5.7-log and a lower 95% confidence level of 5.1-log. Both of these inactivation values exceed the California Title 22 requirement of 5-log virus inactivation for an alternative disinfection technology. Based on the results of this study, the Districts proposed to operate free chlorine disinfection as the first step of sequential chlorination, on filtered effluent at the SJCEWRP under the following conditions:1. Maintain a minimum FCRCT of 9 mg Cl 2 -min/L; 2. Maintain a minimum FCR concentration of 1.0 mg Cl 2 /L; and 3. Maintain a minimum free chlorine modal contact time of 4.0 min. Following a meeting with the California Department of Public Health (CDPH) staff, the Districts expect the CDPH to grant conditional acceptance of sequential chlorination as an alternative for producing disinfected tertiary recycled water at the SJCEWRP before the NPDES and reuse permit for the plant are renewed. WEFTEC 2013