Posted by poolplantcourses.org on Tuesday, June 12, 2012 Under: Pool Water Pollution
Cryptosporidia is a parasite that is of particular concern for pool plant operators because it is not killed by chlorine. The parasites live inside a protective shell called an oocyst which protect them from the chlorine in the swimming pool or spa water. If these oocysts are ingested by swallowing contaminated water, the cryptosporidia with hatch out of the shells and reproduce, causing a gastro-intestinal illness. When the newly-created oocysts are expelled from the body via the faeces, the whole cycle starts again.
As chlorine is an ineffective defence, the pool plant operator must use other methods. The key operational defence is keeping cryptosporidium out of the swimming pool in the first place. Anyone who has been ill with diarrhoea must not go swimming until they are symptom-free for at least 14 days. We recommend putting up some signage about this at reception as well as in the changing rooms etc. You also need to ensure the effective coagulation and filtration of the oocysts. The thing to bear in mind is the fact that without the addition of a coagulant (such as poly-aluminium chloride) to the circulation system at the correct dosing rate, the oocysts will pass straight through the sand in a commercial swimming pool filter. This is because the oocysts are about 5 microns in diameter, whereas the gaps between the sand grains are about 10 microns in width in a ripened sand filter. The addition of a coagulant will cause the minute particles of pollution (including the cryptosporidium oocysts) to clump together to form what are know as 'flocs'. These flocs are large enough so as not to pass through the sand filter and end up in the swimming pool.
Ultra violet radiation and ozone disinfection have been found to eliminate cryptosporidia, but even when using these types of disinfection processes, the use of a coagulant is still recommended.
It is vital that pool plant operators keep their sand filters clean and well-maintained. This means that for swimming pools, the sand filters should be backwashed at least weekly, or according to the filter manufacturers instructions. Spa pool filters should be backwashed every day.
If you end up with loose, runny stool in the swimming pool, you will need to assume that cryptosporidia is present and clear the pool and keep it closed for 6 turnover cycles. While your closed down, backwash the filters, get the chlorine up at the high end of the acceptable range and get the pH at the low end of the acceptable range. Also, scrub, sweep, brush, squeegy, net, hoover the whole area before re-opening.
In : Pool Water Pollution
Tags: "cryptosporidia" "flocs" "coagulation" "filtration"