DISTRIBUTION OF BACTERIA WITHIN OPERATING LABORATORY WATER-PURIFICATION SYSTEMS

Experiments were conducted to measure communities of bacteria within o perating ultrapure water treatment systems intended for laboratory use . Samples from various locations within Milli-Q Plus and Milli-Q UV Pl us systems were analyzed for populations of planktonic bacteria at wee kly intervals over 3 months of operation. Relatively high initial dens ities of planktonic bacteria (102 to 103 bacteria per ml) were seen wi thin both units when they were challenged with source water of poor qu ality, although the product water continued to be acceptable with rega rd to bacterial numbers, resistivity, and endotoxin concentration. Und er more normal operating conditions, significant differences were seen in planktonic populations throughout the systems with excellent produ ct water quality. A great deal of variability was observed in biofilm populations analyzed from various system surfaces after 3 months of op eration. The concentrations of planktonic bacteria and biofilm densiti es were much lower in the unit containing a UV lamp. These findings su ggest that a range of microenvironmental conditions exist within purif ied water systems, leading to variable populations of bacteria. Howeve r, product water of excellent quality was obtained despite the bacteri al communities.