tailieunhanh - Indicators of microbial water quality

Current guidelines in the three water-related areas (drinking water, wastewater and recreational water) assess quality, in microbiological terms, by measuring indicator organisms. This chapter looks at the history and examines some of the methods used to assess the microbiological quality of water, highlighting the current limitations and also possible future developments. | 13 Indicators of microbial water quality Nicholas J. Ashbolt Willie . Grabow and Mario Snozzi Current guidelines in the three water-related areas drinking water wastewater and recreational water assess quality in microbiological terms by measuring indicator organisms. This chapter looks at the history and examines some of the methods used to assess the microbiological quality of water highlighting the current limitations and also possible future developments. INTRODUCTION Traditionally indicator micro-organisms have been used to suggest the presence of pathogens Berg 1978 . Today however we understand a myriad of possible reasons for indicator presence and pathogen absence or vice versa. In short there is no direct correlation between numbers of any indicator and enteric pathogens Grabow 1996 . To eliminate the ambiguity in the term microbial indicator the following three groups outlined in Table are now recognised 2001 World Health Organization WHO . Water Quality Guidelines Standards and Health. Edited by Lorna Fewtrell and Jamie Bartram. Published by IWA Publishing London UK. ISBN 1 900222 28 0 290 Water Quality Guidelines Standards and Health General process microbial indicators Faecal indicators such as E. coli Index organisms and model organisms. Table . Definitions for indicator and index micro-organisms of public health concern see Box for definitions of microbial groups Group Definition Process indicator A group of organisms that demonstrates the efficacy of a process such as total heterotrophic bacteria or total coliforms for chlorine disinfection. Faecal indicator A group of organisms that indicates the presence of faecal contamination such as the bacterial groups thermotolerant coliforms or E. coli. Hence they only infer that pathogens may be present. Index and model organisms A group or species indicative of pathogen presence and behaviour respectively such as E. coli as an index for Salmonella and F-RNA coliphages as models of .