Drinking water disinfection efficiency
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Question
What is the efficiency of drinking water disinfection methods, reported in log-clearance?
Answer
Rationale
Data
| Method | Campylobacter | E.coli O157:H7 | Rotavirus | Norovirus | Sapovirus | Cryptosporidium | Giardia |
|---|---|---|---|---|---|---|---|
| UV | [1] | [1] | [1] | [2] | [2] | [1] | [1] |
| Ozonization | [3] | [3], [2] | [3], [2] | [2] | [3] | [3] |
UV
The CT-values for UV are mW/cm2 * seconds
| Obs | Pathogen | 0 | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|---|---|
| 1 | campylobacter | 0 | 3 | 7 | 10 | 14 | NA |
| 2 | E.coli O157:H7 | 0 | 5 | 9 | 14 | 19 | NA |
| 3 | rotavirus | 0 | 10 | 20 | 29 | 39 | NA |
| 4 | norovirus | 0 | 10 | 21 | 36 | NA | NA |
| 5 | sapovirus | 0 | 10 | 21 | 36 | NA | NA |
| 6 | cryptosporidium | 0 | 3 | 6 | 12 | NA | NA |
| 7 | giardia | 0 | 2 | 5 | 11 | NA | NA |
- E.coli and Campylobacter jejuni corrected for environmental spp.
- Cryptosporidium and giardia: no correction for environmental spp. (research needed).
- Rotavirus SA-11
- For noro: 0.8 log inactivation was estimated for a UV fluence of 20mJ/cm2. At higher fluences (40 and 70mJ/cm^2) all samples were negative. However, it is uncertain to which degree inactivation assessed with RT-PCR is representative for inactivation assessed with infectivity assays.
- For water with low turbidity and high UV transmission?
The log decreases follow the formula [1]
- log10(Nt/N) = -k * Fluence
where Nt is the microbial concentration after contact time t. Fluence is the product of the UV fluence rate (mW/cm2) and the exposure t (mWs/cm2 = mJ/cm2).
OR
- log10(Nt/N) = -k * Fluence - b
where b is the y-intercept. This is used in cases where small amounts of UV don't have an effect, and the log linear decrease only begins at a certain level of UV. For some microbes there is also an upper limit to log decrease, after which adding fluence doesn't decrease the microbe concentration.
Ozone
Ozone decay model:[4]
- C = (C0 - D)exp(-k*t)
Where D is instantaneous demand, k is decay constant, t is time and C is residual
Ozone has a half-life in pure distilled water of approximately 40 min at pH 7.6, but this decreases to 10 min at pH 8.5 at 14.6°C. Rising temperatures increase the rate of decomposition. [5]
| Obs | Pathogen | 0 | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|---|---|
| 1 | campylobacter | 0 | NA | NA | NA | NA | NA |
| 2 | E.coli O157:H7 | 0 | NA | 0.02 | NA | NA | NA |
| 3 | rotavirus | 0 | NA | 0.5 | 0.8 | 1 | NA |
| 4 | norovirus | 0 | NA | 0.5 | 0.8 | 1 | NA |
| 5 | sapovirus | 0 | NA | 0.5 | 0.8 | 1 | NA |
| 6 | cryptosporidium | 0 | 4 | 11 | 22 | NA | NA |
| 7 | giardia | 0 | NA | 1.8-2 | NA | NA | NA |
- E.coli, rota, Giardia muris cysts: temperature 5°C and pH 6-7 [3]
- Giardia: in 15°C demand free buffer water ct required for log-2 0.075-0.9 min*mg/l (50000 cysts - 100 cysts) [6]
- Crypto: in 1°C tap water ct required for log-2 40 min*mg/l, in 20°C tap water 2 min*mg/l[6]
- Cryptosporidium temperature 13°C, also available for 1°C and 22°C[3]
Calculations
CT-value = concentration * time (min)
The code below saves the constant for immediate demand and decay constant as well as the time used as the time ozone affects the water. The current constants are from Haas & Kaymak 2003[4], the averages of the constants they found for different experiments. Their water temperature in all experiments was 15°C and pH approximately 8. The value on time is based on nothing, but a value is needed for the model to run
See also
- Youxian Wu, Thomas Clevenger,* and Baolin Deng 2005. Impacts of Goethite Particles on UV Disinfection of Drinking Water [5]
- Charlotte Farrella, Francis Hassarda, Bruce Jefferson, Tangui Leziarta, Andreas Nocker, Peter Jarvis 2018. Turbidity composition and the relationship with microbial attachment and UV inactivation efficacy. [6]
- John C.H. Chang, Susan F. Ossoff, David C. Lobe, Mark H. Dorfman, Constance M. Dumais, Robert G.Qualls, J. Donald Johnson 1985. UV Inactivation of Pathogenic and Indicator Microorganisms. [7]
- Charles N.Haas, Baris Kaymak 2003. Effect of initial microbial density on inactivation of Giardia muris by ozone. [8]
- Drinking Water and Health: Volume 2. II The Disinfection of Drinking Water [9]
- WHO: Water sanitation and health. Guidelines. 3 Inactivation (disinfection) processes. [10]
- Agnieszka Joanna Brodowska, Agnieszka Nowak, Alina Kondratiuk-Janyska, Marcin Piatkowski, Krzysztof ́Smigielski 2017. Modelling the Ozone-Based Treatments forInactivation of Microorganisms. [11]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Hijnen et al. 2006: Inactivation credit of UV radiation for viruses, bacteria and protozoan (oo)cyst in water: a review. Water Research 40(1) p3-22
- ↑ 2.0 2.1 2.2 2.3 2.4 WHO & OECD 2003: Assessing Microbial Safety of Drinking Water: Improving approaches and methods [1]
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 World Health Organization 2004 Water Treatment and Pathogen Control: Process Efficiency in Achieving Safe Drinking Water: 3 Inactivation (disinfection) processes. Edited by Mark W LeChevallier and Kwok-Keung Au. ISBN: 1 84339 069 8. Published by IWA Publishing, London, UK. [2]
- ↑ 4.0 4.1 Haas CN, Kaymak B. 2003. Effect of initial microbial density on inactivation of Giardia muris by ozone.Water Res. 2003 Jul;37(12):2980-8.
- ↑ Drinking Water and Health, Volume 2. II The Disinfection of Drinking Water. Safe Drinking Water Committee, Board on Toxicology and Environmental Health Hazards, Assembly of Life Sciences. ISBN: 0-309-55406-3, 408 pages, 1980. PDF available from the National Academies Press [3]
- ↑ 6.0 6.1 WQ Betancourt, JB Rose, 2004. Drinking water treatment processes for removal of Cryptosporidium and Giardia. Veterinary Parasitology 126 (2004) 219–234. [4]
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