Occurrence of mycobacteria in water treatment lines and in water distribution systems

Abstract

The frequency of recovery of atypical mycobacteria was estimated in two treatment plants providing drinking water to Paris, France, at some intermediate stages of treatment. The two plants use two different filtration processes, rapid and slow sand filtration. Our results suggest that slow sand filtration is more efficient for removing mycobacteria than rapid sand filtration. In addition, our results show that mycobacteria can colonize and grow on granular activated carbon and are able to enter distribution systems. We also investigated the frequency of recovery of mycobacteria in the water distribution system of Paris (outside buildings). The mycobacterial species isolated from the Paris drinking water distribution system are different from those isolated from the water leaving the treatment plants. Saprophytic mycobacteria (present in 41.3% of positive samples), potentially pathogenic mycobacteria (16.3%), and unidentifiable mycobacteria (54.8%) were isolated from 12 sites within the Paris water distribution system. Mycobacterium gordonae was preferentially recovered from treated surface water, whereas Mycobacterium nonchromogenicum was preferentially recovered from groundwater. No significant correlations were found among the presence of mycobacteria, the origin of water, and water temperature.

FIG. 1.

Locations of the 12 sampling sites within the Paris water distribution system. All the sites were located outside buildings. The origins of the water collected at the 12 selected sites are indicated. The locations of the two water treatment plants are indicated by arrows.

FIG. 2.

Schematic diagram of the two treatment plants in which different preliminary treatment processes (rapid and slow sand filtration processes) are used. The dotted lines delimit the main clarification and disinfection steps. The locations of the sampling sites in the two treatment lines are indicated by dashed arrows.