Enumeration of faecal indicator bacteria in large water volumes using on site membrane filtration to assess water treatment efficiency

With sample volumes as tested in routine microbiological monitoring for the presence and absence of faecal indicator bacteria in treated water the act ual concentration in the final stages of water treatment cannot be assessed . Consequently, no accurate information can be obtained about the removal e fficiency of a water treatment for microorganisms. Therefore a method for o n site isolation of faecal indicator bacteria from large volumes (1001 or m ore) of treated water using membrane filtration (MF-sampling) was developed and tested. The procedures for culturing the isolated microorganisms were similar to those applied in the routine methods for small volumes,using mem brane filtration (mf-method). The recovery efficiency of MF-sampling for E. coli, S. faecalis and spores of sulphite-reducing clostridia ranged from 7 4.6 to 100% and only for E. coli a slight decrease with increasing sample v olume was found. Field studies revealed that MF-sampling can easily be impl emented in (routine) laboratory practice for an accurate determination of t he concentration of faecal indicator bacteria in treated water after variou s treatment stages. From these data the treatment efficiency of the involve d processes and the overall treatment for those microorganisms and the fluc tuation in microorganism removal were determined. Such data can be used to improve water treatment regarding the removal of microorganisms. Validation of the use of faecal indicator bacteria asa surrogate parameter for the as sessment of the effects of treatment processes on pathogenic microorganisms needs further investigation. (C) 2000 Elsevier Science Ltd. All rights res erved.