Indicator bacteria concentrations in water treatment and assessment of elimination capacity (THESIS VERSION)

Abstract

The use of thermotolerant coliforms (Coli44) and spores of sulphitereducing clostridia (SSRC) as process indicators to assess the elimination capacity of water treatment and unit processes for pathogenic microorganisms susceptible and resistant to disinfection was explored. Historical data sets of routine monitoring programs revealed that both indicators were detected in the finished water after treatment in variable frequencies. Coli44 was detected incidentally, whereas SSRC was observed after every treatment in percentages of samples ranging from 0.8 up to 23%. With data collected after unit processes efficacy of these unit processes was calculated to eliminate both process indicators. The percentage of positive samples, however, decreased rapidly during treatment. This affects the accuracy of the calculated decimal elimination capacity (DEC). Decreasing the detection limit of the standard membrane filtration method by filtering larger sample volumes enabled more accurate assessment of DEC. The required detection limit of the analytical method, however, to evaluate the required DEC of a total water treatment for pathogenic micro-organisms is ≤1 organism per 100 l which requires further research for new methods.