Cryptosporidia
Posted by poolplantcourses.org on Saturday, December 17, 2011 Under: Pool Water Pollution
Cryptosporidia is an organism that pool operators need to be particularly aware of. The main problem with it is that the chlorine in the pool water will not kill it due to the fact that it is protected within a shell that the chlorine will not penetrate. Cryptosporidia causes an acute gastro-intestinal illness and is introduced into the pool water via faecal contamination. If someone has an accident in the pool and the result is a loose, as opposed to solid stool, you as pool operator are going to have to assume that cryptosporidium is present. Therefore, you will need to get everyone out (because the chlorine won't kill it) and then take steps to remove the contaminant via mechanical means (ie, scoops, nets, hoover at the pool and then coagulation and filtration in the plant room). Two main things to consider are:
1. Cryptosporidia is about 5 microns wide (a micron is 1/1000th of a millimetre) and the spaces in between sand grains in a conventional swimming pool filter are about 70 microns just after an effective backwash and about 5 - 10 microns when ripened. As you can see, cryptosporidia will be small enough to pass through. In order to deal with this problem you will need to add a coagulant to the pool water circulating around the system, before the point when it enters the top of the filter. This is usually an aluminium based compound that will cause fine particles of pollution to bind together to form what are know as 'flocs' which are big enough to become trapped by the filter media.
2. Not all of your pool water will pass through the circulation system during your turnover period. The turnover period refers to the time it takes for an equivalent volume of water to pass through. Some 'bits' of water will pass through a few times, some other 'bits' might not pass through at all during a single turnover period. This is affected by how well your pool water mixes together due to things like the number and position of inlets and outlets in relation to each other, the pool water velocity around the system, the number of people in the pool and how much they are moving etc. This is the reason why your emergency procedures in the event of faecal contamination should stipulate than the pool remain closed for 6 turnover periods in order to be reasonably sure that all of the cryptosporidia has been removed from all of the pool water.
1. Cryptosporidia is about 5 microns wide (a micron is 1/1000th of a millimetre) and the spaces in between sand grains in a conventional swimming pool filter are about 70 microns just after an effective backwash and about 5 - 10 microns when ripened. As you can see, cryptosporidia will be small enough to pass through. In order to deal with this problem you will need to add a coagulant to the pool water circulating around the system, before the point when it enters the top of the filter. This is usually an aluminium based compound that will cause fine particles of pollution to bind together to form what are know as 'flocs' which are big enough to become trapped by the filter media.
2. Not all of your pool water will pass through the circulation system during your turnover period. The turnover period refers to the time it takes for an equivalent volume of water to pass through. Some 'bits' of water will pass through a few times, some other 'bits' might not pass through at all during a single turnover period. This is affected by how well your pool water mixes together due to things like the number and position of inlets and outlets in relation to each other, the pool water velocity around the system, the number of people in the pool and how much they are moving etc. This is the reason why your emergency procedures in the event of faecal contamination should stipulate than the pool remain closed for 6 turnover periods in order to be reasonably sure that all of the cryptosporidia has been removed from all of the pool water.
In : Pool Water Pollution
Tags: cryptosporidia coagulation micron