Journal of Water and Health Vol 5 No 3 pp 433–440 © IWA Publishing 2007 doi:10.2166/wh.2007.039
The efficiency of ozonated water from a water treatment plant to inactivate Cryptosporidium oocysts during two seasonal temperatures
T. Wohlsen, S. Stewart, P. Aldridge, J. Bates, B. Gray and M. Katouli
Public Health Microbiology, Queensland Health Scientific Services, PO Box 594 Archerfield, Queensland 4108, Australia Tel.: +61 7 3274 9075Fax: +61 7 3274 9175tracey_wohlsen@health.qld.gov.au
Faculty of Science, University of the Sunshine Coast, Sippy Downs, Queensland 4556, Australia
Aquagen, Water and Renewable Energy, Palmwoods, Queensland 4555, Australia
Public Health Microbiology, Queensland Health Scientific Services, Coopers Plains, Queensland 4108, Australia
Faculty of Science, University of the Sunshine Coast, Sippy Downs, Queensland 4556, Australia
ABSTRACT
We investigated the efficiency of residual ozone from an advanced water treatment plant with an applied dose of 2.5 mg l-1 to inactivate viable Cryptosporidium oocysts during summer (i.e. 24°C) and winter (i.e. 18.9°C) in Queensland, Australia. Containers for sample collection were inoculated with 1,000 oocysts l-1 and filled with ozonated water. Ozone residual concentrations were measured at 0, 5 and 10 min intervals. Viability was determined by excystation. Non-ozonated water from the plant, trip and laboratory controls were also analysed. The applied ozone dose of 2.5 mg l-1 produced an immediate residual concentration of 1.25 mg 1-1 at 24°C and 1.34 mg 1-1 at 18.9°C in unseeded samples. The initial ozone residual in seeded containers was 1.22±0.03 mg 1-1 at 24°C and 1.37±0.04 mg 1-1 at 18.9°C. There was a gradual increase in inactivation of oocysts, with 49% of oocysts inactivated at 0 min to 92% after 10 min at 24°C and 57% at 0 min to 92.8% at 10 min at 18.9°C.
Keywords: Cryptosporidium; excystation; inactivation; ozone; temperature
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