Synergy in sequential inactivation of Cryptosporidium parvum with ozone/free chlorine and ozone/monochloramine

The main objective of this study was to investigate the inactivation kineti cs of Cryptosporidium parvum oocysts with sequential disinfection schemes i nvolving ozone as a primary disinfectant, and free chlorine or monochlorami ne as a secondary disinfectant. Two types of synergistic effects were obser ved. Ozone pre-treatment resulted in the removal of the relatively more pro nounced initial lag phases observed for monochloramine and hypochlorous aci d. An additional and more important synergistic effect was an enhancement i n the rate of secondary inactivation with both hypochlorous acid and monoch loramine after complete removal of the lag phase by ozone pretreatment. A s tronger synergy was observed at a lower temperature. The secondary inactiva tion rate was 1.1-2.8 (hypochlorous acid) and 2.4-9.2 (monochloramine) time s faster than the corresponding post lag-phase primary inactivation rate at respective temperatures of 30-10 degreesC. Consistency between the two via bility assessment methods, modified in-vitro excystation and animal infecti vity, was demonstrated or shown for both primary inactivation with ozone an d secondary inactivation with ozone/monochloramine. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.