I really appreciated your article on “Obstacles to Black Swimming.” I teach swimming in physical education at a middle school in Minnesota and have encountered several of those problems.
The girls are concerned about their hair and don’t think they can get it wet, they wear big t-shirts over their swimming suits (which makes it even harder to swim), and most of them have not had lessons before.
Cynthia Jones
Aquatic Instructor / Coach
St. Michael – Albertville Middle School
Albertville, Minn.
Monday, March 31, 2008
Law of Dilution Must Be Considered for UV Effectiveness
The recent article in the October 2007 issue titled “Cryptosporidium Strikes Pools Across Nation” is effective in raising (or maintaining) the awareness of crypto in the swimming pool industry.
It states that an outbreak even occurred at a swimming pool that had recently installed a UV system. The article is correct in stating that water clarity does determine the effectiveness of Ultra Violet (UV). However, it should be kept in mind that UV systems are used to treat drinking and wastewater. Wastewater is much more turbid than normal pool water, therefore UV should perform exceptionally well in normal pool water clarity. The article insinuates that the swimming pool water where the outbreak occurred with a UV system had turbid water. As I’m not associated with this pool I have no idea if the water was turbid or not. An outbreak of crypto at a swimming pool with a UV system can be attributed to things other than turbidity such as turnover.
Swimmers are at risk at all times whether there is or is not an ancillary sterilization system such as UV or Ozone.
It also stated that the pathogen can’t be killed until it goes through the system, which occurs about once every six hours. The first portion of the sentence is correct in that the pathogen must pass through the UV system to be inactivated. However, the second part of the statement is incorrect.
Every drop of water does not typically pass through the system in six hours. How much water passes through the system depends upon the number of turnovers. A system that has four turnovers per day means that the total pool volume of water has passed through the pools filter system 4 times in a 24 hour period.
This means that the total amount of the pool’s water volume has passed through the filter system every 6 hours (24 hours / 4 turnovers per day). UV systems are designed to treat the full (100 percent) flow of water.
Gage & Bidwell’s Law of Dilution shows us that in those same six hours only approximately 58 percent of every drop of water went through the system in the first turnover even though the system saw the total volume of the pool. The system saw some of the same water over and over again. After two turnovers the system has seen 84 percent of the water, after three turnovers 95 percent and after the fourth turnover (24 hours) 98 percent of every drop of water has finally seen the filter and UV system.
People can be exposed for far longer than the 6 hours indicated in the article. It takes 24 hours (in the example above) before 98 percent of the water is treated, therefore people could be exposed for 24 hours or longer.
This is a significant difference in possible exposure time and the ability for cryptosporidium (or any other pathogen) to multiply and infect people.
It is a misconception that because there is chlorine in the water that the water is pathogen free. Likewise it is a misconception that because there is a UV or ozone system the water is pathogen free. Pathogens take time to destroy. Likewise it takes time to destroy the pathogens with a UV system. They are immediately inactivated upon exposure to the UV light, but it takes time to get them to pass through the system.
In the meantime, swimmers are at risk to exposure. Chlorine at 1 ppm can take 6.7 days to destroy cryptosporidium whereas the UV will destroy it as soon as the crypto passes through the UV system. 6.7 days versus 24 hours. I’ll take the 24 hours.
Decisions are made based upon the information we provide them. Misinformation to the aquatics operators and the public can do harm to our industry, especially when making people think they are safe when they are not.
It is the responsibility of owners and operators to minimize the risk/exposure, as it can never be eliminated completely. It is also our responsibility to educate the aquatics industry and the public. With that in mind it best to spread the following:
• minimize or eliminate shoes from the deck/pool area
• all swimmers/patrons should thoroughly shower with soap and water prior to entering any pool/spa
• if anyone experiences diarrhea then they should not go in the water for a minimum of two weeks after the symptoms have cleared up.
We do advocate the use of Ultra Violet (UV) systems to inactivate pathogens and destroy chloramines. This is another powerful weapon in our aquatics arsenal.
Steve Dunn
Vice President, Sales
Commercial Pool Systems, Inc.
Martinez, Calif.
It states that an outbreak even occurred at a swimming pool that had recently installed a UV system. The article is correct in stating that water clarity does determine the effectiveness of Ultra Violet (UV). However, it should be kept in mind that UV systems are used to treat drinking and wastewater. Wastewater is much more turbid than normal pool water, therefore UV should perform exceptionally well in normal pool water clarity. The article insinuates that the swimming pool water where the outbreak occurred with a UV system had turbid water. As I’m not associated with this pool I have no idea if the water was turbid or not. An outbreak of crypto at a swimming pool with a UV system can be attributed to things other than turbidity such as turnover.
Swimmers are at risk at all times whether there is or is not an ancillary sterilization system such as UV or Ozone.
It also stated that the pathogen can’t be killed until it goes through the system, which occurs about once every six hours. The first portion of the sentence is correct in that the pathogen must pass through the UV system to be inactivated. However, the second part of the statement is incorrect.
Every drop of water does not typically pass through the system in six hours. How much water passes through the system depends upon the number of turnovers. A system that has four turnovers per day means that the total pool volume of water has passed through the pools filter system 4 times in a 24 hour period.
This means that the total amount of the pool’s water volume has passed through the filter system every 6 hours (24 hours / 4 turnovers per day). UV systems are designed to treat the full (100 percent) flow of water.
Gage & Bidwell’s Law of Dilution shows us that in those same six hours only approximately 58 percent of every drop of water went through the system in the first turnover even though the system saw the total volume of the pool. The system saw some of the same water over and over again. After two turnovers the system has seen 84 percent of the water, after three turnovers 95 percent and after the fourth turnover (24 hours) 98 percent of every drop of water has finally seen the filter and UV system.
People can be exposed for far longer than the 6 hours indicated in the article. It takes 24 hours (in the example above) before 98 percent of the water is treated, therefore people could be exposed for 24 hours or longer.
This is a significant difference in possible exposure time and the ability for cryptosporidium (or any other pathogen) to multiply and infect people.
It is a misconception that because there is chlorine in the water that the water is pathogen free. Likewise it is a misconception that because there is a UV or ozone system the water is pathogen free. Pathogens take time to destroy. Likewise it takes time to destroy the pathogens with a UV system. They are immediately inactivated upon exposure to the UV light, but it takes time to get them to pass through the system.
In the meantime, swimmers are at risk to exposure. Chlorine at 1 ppm can take 6.7 days to destroy cryptosporidium whereas the UV will destroy it as soon as the crypto passes through the UV system. 6.7 days versus 24 hours. I’ll take the 24 hours.
Decisions are made based upon the information we provide them. Misinformation to the aquatics operators and the public can do harm to our industry, especially when making people think they are safe when they are not.
It is the responsibility of owners and operators to minimize the risk/exposure, as it can never be eliminated completely. It is also our responsibility to educate the aquatics industry and the public. With that in mind it best to spread the following:
• minimize or eliminate shoes from the deck/pool area
• all swimmers/patrons should thoroughly shower with soap and water prior to entering any pool/spa
• if anyone experiences diarrhea then they should not go in the water for a minimum of two weeks after the symptoms have cleared up.
We do advocate the use of Ultra Violet (UV) systems to inactivate pathogens and destroy chloramines. This is another powerful weapon in our aquatics arsenal.
Steve Dunn
Vice President, Sales
Commercial Pool Systems, Inc.
Martinez, Calif.
Subscribe to:
Posts (Atom)
