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Occurrence of Cryptosporidium Oocysts in Leisure Pools in the UK, 2017, and Modelling of Oocyst Contamination Events
Article

Revisiting the Gage–Bidwell Law of Dilution in Relation to the Effectiveness of Swimming Pool Filtration and the Risk to Swimming Pool Users from Cryptosporidium

1
Pool Sentry Ltd., Dale Cottage, Stanton Dale, Ashbourne DE6 2BX, UK
2
School of Architecture, Building and Civil Engineering, Loughborough University, Ashby Road, Loughborough LE11 3TU, UK
3
Civil and Environmental Engineering, University of North Carolina at Charlotte, 9201 University City Blvd., Charlotte, NC 28223-0001, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Helvi Heinonen-Tanski
Water 2021, 13(17), 2350; https://doi.org/10.3390/w13172350
Received: 30 June 2021 / Revised: 14 August 2021 / Accepted: 23 August 2021 / Published: 27 August 2021
(This article belongs to the Special Issue Healthy Recreational Waters: Sanitation and Safety Issues)
The transfer of water from a swimming pool to the treatment location is key in determining the effectiveness of water treatment by filtration in removing turbidity and managing the risk from particulate material, including microbial pathogens, such as Cryptosporidium spp. A key recommendation for pool operators when dealing with an accidental faecal release (the likely main source of high Cryptosporidium oocyst concentrations in pools) is that the pool water should be filtered for at least six turnover cycles prior to use. This paper briefly outlines the theoretical basis of what has become known as the Gage–Bidwell Law of Dilution, which provides a basis for this recommendation, and extends the idea to account for the impact of filter efficiency. The Gage–Bidwell Law reveals that for each pool turnover 63% of the water resident in the pool at the start of the turnover period will have been recirculated. Building on this, we demonstrate that both filter efficiency and water-turnover time are important in determining filtration effectiveness and can be combined through a single parameter we term ‘particle-turnover’. We consider the implications of the Gage–Bidwell Law (as referred to in the original 1926 paper) for the dynamics of the ‘dirt’ content of pool water, whether in terms of a specific particle size range (e.g., Cryptosporidium oocysts) or turbidity. View Full-Text
Keywords: Cryptosporidium oocyst; filtration; Gage–Bidwell Law; particle-turnover; pools; turbidity Cryptosporidium oocyst; filtration; Gage–Bidwell Law; particle-turnover; pools; turbidity
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MDPI and ACS Style

Simmonds, L.P.; Simmonds, G.E.; Wood, M.; Marjoribanks, T.I.; Amburgey, J.E. Revisiting the Gage–Bidwell Law of Dilution in Relation to the Effectiveness of Swimming Pool Filtration and the Risk to Swimming Pool Users from Cryptosporidium. Water 2021, 13, 2350. https://doi.org/10.3390/w13172350

AMA Style

Simmonds LP, Simmonds GE, Wood M, Marjoribanks TI, Amburgey JE. Revisiting the Gage–Bidwell Law of Dilution in Relation to the Effectiveness of Swimming Pool Filtration and the Risk to Swimming Pool Users from Cryptosporidium. Water. 2021; 13(17):2350. https://doi.org/10.3390/w13172350

Chicago/Turabian Style

Simmonds, Lester P., Guy E. Simmonds, Martin Wood, Tim I. Marjoribanks, and James E. Amburgey 2021. "Revisiting the Gage–Bidwell Law of Dilution in Relation to the Effectiveness of Swimming Pool Filtration and the Risk to Swimming Pool Users from Cryptosporidium" Water 13, no. 17: 2350. https://doi.org/10.3390/w13172350

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