CHARACTERIZATION OF AMOEBAE AND EVTRA-AMOEBAL BACTERIA IN DRINKING WATER, AND IDENTIFICATION OF CONTROL STRATEGIES

摘要

Free-living amoebae have been detected in a large number of man-made water systems, including drinking water distribution systems. Some of these amoebae can harbour amoebae-resisting bacteria, and thus potentially act as reservoirs and vehicles for a number of pathogens. The objectives of this study were to quantify the free-living amoebae present at different steps of drinking water production and distribution, assess their potential association with Legionella spp., and identify possible control strategies. Sampling campaigns were conducted in Europe on a series of drinking water treatment plants supplied by different surface waters and applying different treatment technologies. The results of this study confirm the presence of free-living amoebae in surface waters used for drinking water production. Although surface water treatment chains significantly reduce their numbers, they do not eliminate them totally. Moreover, when encysted, these micro-organisms are highly resistant to disinfectants. Consequently, control strategies in drinking water production should be principally based on physical removal processes such as clarification and granular or membrane filtration. Biofilms and sediments constitute ideal niches where they can feed on bacteria but also where they can occasionally become infected by amoebae-resisting bacteria. Consequently, control strategies in drinking water production and distribution should also include good management of sludge from clarifiers, of filter backwash, and biofilm and sediment control in distribution systems.