For those that swear by UV disinfection

[tim5055]

Local, state and federal health officials are investigating after an Ohio teenager died from a brain-eating amoeba days after visiting the Whitewater Center in Charlotte.

Rafting activities closed at Whitewater Center after deadly amoeba found | WSOC-TV

The US National Whitewater Center sources its water from the Charlotte Mecklenburg Utilities Department and two wells located on the premises. The water contained in the whitewater channels is in a closed loop system comprised entirely of concrete. The water is disinfected with ultraviolet radiation and filtered with a disc filtration system. The UV system is a constant application and treats 12 million gallons of water every 24 hours which is the total volume of the system. In addition to the UV treatment, the Center periodically augments that treatment through the injection of chlorine into the system.

The levels of UV radiation disinfection utilized every day, continuously, at the Center are sufficient to “inactivate” the water born amoeba in question to an effective level of 99.99%"

 

[zea3]

Interesting, they can "inactivate" the amoeba up to 99.99%, but most of the 11 water samples taken show high levels of the amoeba. Someone's math is a bit off. I wonder how much chlorine they inject and how periodically.

 

[JVTrain]

I wonder how much chlorine they inject and how periodically.

Apparently, not enough.

 

[JoyfulNoise]

From here -
Pathogen & Environment | Naegleria fowleri | CDC

Disinfection: Naegleria fowleri trophozoites and the more resistant cysts are sensitive to disinfectants like chlorine 9, 11-15 and monochloramine 15, 16. Chlorine is the most common disinfectant used to treat drinking water and swimming pools. The chlorine sensitivity of Naegleria fowleri is moderate and in the same range as the cysts from Giardia intestinalis, another waterborne pathogen 17, 18. The inactivation data for Naegleria is limited but recent CT values (concentration of disinfectant [mg/l] X contact time [in minutes]) have been developed 14. Under laboratory conditions, chlorine at a concentration of 1 ppm (1 mg/L) added to 104.4°F (38°C) clear (non-turbid) well water at a pH of 8.01 will reduce the number of viable and more resistant Naegleria fowleri cysts by 99.99% (4 logs) in 56 minutes (CT of 56) 14. Cloudy (turbid) water requires longer disinfection times or higher concentrations of disinfectant.

This paper in the reference section (http://www.awwa.org/publications/journal-awwa/abstract/articleid/29961635.aspx) indicates that the UV inactivation times for the Naergleria parasite is actually LONGER (i.e., harder to kill with UV) than cryptosporidium which is often cited as one of the reasons to use UV.

So, if they had used proper chlorination (1ppm FC with 0 CYA), the pathogen would have been killed. But instead, they chose to use a UV system and "some regular chlorination" which actually made it HARDER to kill pathogens like that...and my wife wonders why when we go on vacation that I choose not to go into swimming pools....

[EDIT]

Do note that in the laboratory tests, 1ppm FC was added to 104F water at a pH of 8. This would be closer to spa and hot tub conditions rather than pools which are at least 15F cooler (on average) and a lower pH range (7.5-7.8 typically). So the quoted inactivation times are not quite the same. I'd have to purchase the paper to see the details of the experiment in order to figure out how the quoted CT times for chlorine would translate when considering a pool water environment.
[END-EDIT]

 

[JoyfulNoise]

This paper in the reference section (http://www.awwa.org/publications/journal-awwa/abstract/articleid/29961635.aspx) indicates that the UV inactivation times for the Naergleria parasite is actually LONGER (i.e., harder to kill with UV) than cryptosporidium which is often cited as one of the reasons to use UV.

The paper is actually free for download in PDF format. These are measured CT inactivation times for Naegleria fowleri trophozoite (a trophozoite is just the point in the organisms lifecycle at which it turns into a freely moving parasite capable of consuming tissue for feeding purposes. Parasites like this have complicated cellular lifecycles where they exist in different stages of growth and development) -

1ppm FC at pH of 7.5 in a buffered, demand-free (BDF) water sample:

log₁₀ reduction ................... CT Inactivation Time
2 (99%) ............................................... 6
3 (99.9%) ............................................ 9
4 (99.99%) .......................................... 12

UV Light Disinfection in the same water medium :

log₁₀ reduction ................... CT Inactivation Time
2 (99%) ............................................... 13
3 (99.9%) ............................................ 18
4 (99.99%) .......................................... 24

So one can see that UV alone is about half as effective as chlorine in killing or inactivating N. fowleri. The author in the paper surmises that, being a waterborne organism that exists in surface waters that are constantly exposed to UV light, it likely has DNA repair mechanisms that make UV disinfection more difficult as compared to pathogens like cryptosporidium which are not typically found in open waters and not accustomed to UV light.

At the end of the day this is a sad story for the family involved. No parent should ever have to bury their child and, if this water park was negligent in maintaining a sanitary water environment, this family would be well within rights to seek justice through criminal/civil legal actions.

 

[banditig]

Also the they need an expensive meter to check the UVC output, just because the bulbs work does not mean UVC is being produced, they decay over time like tanning beds

 

[AUSpool]

Assuming the effective sterilisation of a total of 12 million gallons, a 99.99% disinfection rate leaves 1,200 gallons of untreated water and as Matt said, UV only treats the free floating lifecycle stage of a protozoan.

I don't know how the 99.99% disinfection rate was derived but I recall an equation presented by Escobal, 1996, that includes various coefficients for percentage sterilisation to account for the fact that systems with external reaction chambers will always retreat a small portion of previously treated water. The equation is given as;

T = a(G/F)

Where;
T = time as hours of sterilisation required
G = gallons, net volume of system - I always thought V for volume would be better
F = flow rate
a = purity coefficient where at;
99.00000% sterilisation a = -4.6
99.90000% sterilisation a = -6.9
99.99000% sterilisation a = -9.2
99.99900% sterilisation a = -11.5
99.99990% sterilisation a = -13.8
99.99999% sterilisation a = -16.1
100.00000% sterilisation a = Infinite

Iron and humic concentrations are not given but since the water is sourced from two wells I would assume there would be iron in the water. Baird and Cann, 2005, state that both iron and humic substances absorb UV light and reduce the effectiveness of UV sterilisation.

 

[JoyfulNoise]

Assuming the effective sterilisation of a total of 12 million gallons, a 99.99% disinfection rate leaves 1,200 gallons of untreated water and as Matt said, UV only treats the free floating lifecycle stage of a protozoan.

I don't know how the 99.99% disinfection rate was derived but I recall an equation presented by Escobal, 1996, that includes various coefficients for percentage sterilisation to account for the fact that systems with external reaction chambers will always retreat a small portion of previously treated water. The equation is given as;

T = a(G/F)

Where;
T = time as hours of sterilisation required
G = gallons, net volume of system - I always thought V for volume would be better
F = flow rate
a = purity coefficient where at;
99.00000% sterilisation a = -4.6
99.90000% sterilisation a = -6.9
99.99000% sterilisation a = -9.2
99.99900% sterilisation a = -11.5
99.99990% sterilisation a = -13.8
99.99999% sterilisation a = -16.1
100.00000% sterilisation a = Infinite

Iron and humic concentrations are not given but since the water is sourced from two wells I would assume there would be iron in the water. Baird and Cann, 2005, state that both iron and humic substances absorb UV light and reduce the effectiveness of UV sterilisation.

From the paper cited above -

Log10 survival of cysts was taken for each experiment to plot the inactivation curve against UV dose. Chick’s law (Nt/N0) = e^-kit was used to obtain the log10 survival of cysts, in which Nt = the number of cysts at time t (time of UV exposure), N0 = number of cysts at time zero without application of UV light to sample, k = inactivation rate constant or slope of inactivation curve, i = intensity of UV light energy (mW/cm2), and t = exposure time.

The water park operators probably just simply parrot the UV industry trade publications on the CT times. Anyone reading this paper will see right away that there is a defect in using the quoted deactivation times - the experiments use buffered, demand-free water samples (demand free = no sources of chlorine demand OR, in the case of UV, no sources of UV absorption). So, in a real world pool, there would need to be some scaling factor to these kill times because, as you rightly point out, the water will contain both sources of UV absorption as well as sources of light scattering (particulates or turbidity).

 

[ned8377]

This so called brain eating amoeba is present in all surface water such as lakes and rivers. Anyone who has ever been in a lake or river has probably swallowed the amoeba. This unfortunate incident probably occurred through nasal injection or water getting in the nose. There may have been an area of her nasal passage that allowed the amoeba to travel to the brain. This is very unusual but they feel that this is the most likely route. There is no way to completely remove the amoeba from the water or from any lake or river. This is just an unfortunate incident.

 

[JoyfulNoise]

Follow up to the investigation cross-posted here - NC - Algae Weakened Defense Against Illness

Essentially the analysis concludes that algae build up in their water system (they use a lot of concrete culverts and retention ponds) allowed the pathogenic amoeba to grow and survive without being exposed to their disinfection system. This is precisely why it is important to have a residual sanitizer in the water as not all pathogens like algae and bacteria are planktonic - they will naturally form algae mats and biofilms. Once fixated onto a surface, even chlorine can have a hard time eradicating it.

A sad way to learn a valuable lesson...heart-breaking, really.

 

[borjis]

wow....just....wow.

Makes me not want to swim in a river or lake again. Fine by me, I have a pool.