DIRECT BIOFILM MEASUREMENT IN POTABLE WATER: AN EVALUATION OF THE BACTERIAL REGROWTH RISK IN DISTRIBUTION SYSTEMS

摘要

The many studies done on bacterial regrowth phenomena in drinking water distributionrnsystems have clearly shown the importance of biofilms attached at the inner surface of thernpipe. So, these attached microorganisms may represent potential contamination sourcesrnand provide habitats for opportunistic pathogenic microorganisms. To well understandrnbacteriological phenomena that occur in the network, it is indispensable to quantify thesernattached biomasses. A lot of analytical methods have been developed to characterize thernbiofilm in waste water treatment, but only few already existed for potable water. To haverna more accurate characterization of the biofilm, the development of methods for a directrnmeasurement of the biofilm on its substratum may be a good approach. All of thernmethods developed are directly applied to the biofilm attached to its substratum. Therndifferent methods are: TOC measurement (H_2SO_4 acid hydrolysis + UV-persulfaternoxydation), Polysaccharides measurement (colorimetric method), PicoGreena DNArnquantification, Proteins measurement (BCA method), INT Redox probe (ethanolrnextraction), Potential Exoproteolytic Activity. Glass beads, (Dia.: 5 mm) introduced inrnPVC columns with an up-flow water feeding, are used to support biofilm growth and tornfinalize the different protocols. A kinetic approach was chosen to validate the analyticalrnmethods with different water qualities. A weekly sampling of beads from differentrncolumns was carried out during 3 to 4 weeks. In parallel, Heterotrophic Plate Countsrn(HPC) on R2A medium and ATP measurement were done after biofilm removal using anrnultrasonic bath. On sand filtered water, a good correlation was obtained between all ofrnthese methods and also with HPC. So, each methods can be use to follow the biofilmrngrowth kinetics. On finished water, COT and polysaccharides have been abandonedrnbecause of their poor detection limit. Good correlation between the other methods andrnalso with HPC are observed. In addition to that, biofilm measurement responses were inrnaccordance to the composition of the different water qualities tested. So, these methodsrncan be used to evaluate the Biofilm Growth Potential Risk of different kinds of finishedrnwater.