Elimination of micro-organisms in water treatment

Abstract

Clean water supply and sanitation are regarded as major milestones in medical advances since the 19th century. Production and control of microbiologically safe drinking water has been an important challenge for the drinking water industry ever since. Based on recent progress in scientific literature the group of emerging waterborne pathogens has been changed and extended compared to well known pathogenic diseases in the early days (Cholera, Typhus). Epidemiological studies and outbreak reports have identified persistent protozoa Cryptosporidium and Giardia, but also bacteria such as Campylobacter and pathogenic E. coli and enteroviruses as waterborne pathogens. Quantitative Knowledge on dose-response for these pathogens enabled the introduction of a health based target in microbiological water quality control to minimize the risk of infection. In this thesis studies are presented aimed at quantifying the elimination of pathogenic micro-organisms in water treatment processes. Direct monitoring of these pathogens is not feasible. Monitoring of faecal indicator bacteria E. coli and spores of sulphite-reducing clostridia as process indicators susceptible and resistant to disinfectants in water treatment have been explored as an alternative method. The detection limit of the standard enumeration method for these bacteria was decreased for that reason. Additional methods were required for the water treatment processes slow sand filtration, surface water infiltration and UV disinfection and also for validation of the use of both bacteria as process indicators for elimination of pathogens. Elimination of multiple pre-cultured micro-organisms by disinfection and filtration processes is assessed in challenge tests and from literature studies at different scales. These data are compared with the elimination of indigenous organisms. On the basis of the results of these studies a generic methodology is proposed to assess the elimination capacity of the water treatment of a drinking water facility as input for the mandatory Quantitative Microbial Risk Analysis to evaluate the health based target for safe drinking water introduced in the revised legislation.