Removal of Cryptosporidium by high rate contact filtration: the performance of the Prospect Water Filtration Plant during the Sydney water crisis

In Sydney, Australia, during July, August and September 1998, three compreh ensive boil water notices were issued in response to the detection of eleva ted concentrations of Giardia and Cryptosporidium in the water system. Whil e the incidence of illness did not increase above background levels, the po litical impact of these events was sufficient to initiate a full-scale judi cial inquiry. The treatment plants came under intense scrutiny, particularl y the Prospect Water Filtration Plant, which provides for approximately 85% of Sydney's drinking water demand. As part of the investigation, detailed audits of the Prospect Plant were carried out and Cryptosporidium parvum se eding experiments were undertaken in a prototype plant in order to assess t he removal capability of the Prospect filtration process. The overview of t he Plant performance and the results of the Cryptosporidium seeding runs pr esented in this paper confirm that the Prospect Water Filtration Plant was achieving at least 3 logs pathogen removal prior to and during the contamin ation events.