The efficiency of ozonated water from a water treatment plant to inactivate Cryptosporidium oocysts during two seasonal temperatures

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.