Experiments were conducted to measure communities of bacteria within operating ultrapure water treatment systems intended for laboratory use. Samples from various locations within Milli-Q Plus and Milli-Q UV Plus systems were analyzed for populations of planktonic bacteria at weekly intervals over 3 months of operation. Relatively high initial densities of planktonic bacteria (102 to 103 bacteria per ml) were seen within both units when they were challenged with source water of poor quality, although the product water continued to be acceptable with regard to bacterial numbers, resistivity, and endotoxin concentration. Under more normal operating conditions, significant differences were seen in planktonic populations throughout the systems with excellent product water quality. A great deal of variability was observed in biofilm populations analyzed from various system surfaces after 3 months of operation. The concentrations of planktonic bacteria and biofilm densities were much lower in the unit containing a UV lamp. These findings suggest that a range of microenvironmental conditions exist within purified water systems, leading to variable populations of bacteria. However, product water of excellent quality was obtained despite the bacterial communities. The efficient operation of water purification systems is important since the microbiological quality of ultrapure water is of fundamental concern in laboratory science, medicine, and a wide range of industries. Bacterial growth and biofouling within these systems present potentially serious problems for these applications because of biodeterioration and the presence of bacteria or their products in the purified water (19, 20). Despite this significance, surprisingly little research has focused on the microbiology of these systems, and no comprehensive studies have addressed their * Corresponding author.

Processing time and need for technical expertise were significantly reduced with the completely automated functionally closed glycerolization procedure with the high-separation bowl in the Haemonetics ACP 215 instrument.

Abstract--Adsorption of Co 2+ and Cd ~+ on Wyoming montmorillonite was studied by the batch equilibration technique, as a function of salt concentration (0.01-4 M NaC1 and NaNO3), pH (5.0-6.5), adsorbate concentration (trace-10 -2 moles/liter), and presence of complexing ions. Comparison was made with the adsorbability of Sr 2+, known to follow simple ion-exchange equations. The distribution coefficients for Co and Cd in noncomplexing media varied with salt concentration (from -500 liters/kg in 0.01 M Na § to -10 liters/kg in 1 M Na+; pH = 5), but to a lesser extent than that of St. Adsorbability varied also with pH (-1 order of magnitude/pH unit), especially at high ionic strength, compared to a negligible pH effect on Sr. The distribution coefficients of Cd and Co decreased with increasing loading on the clay at a very low percentage (0.2%) of the ion-exchange capacity compared to Sr (20%). These data suggest two classes of sites participating in the adsorption of Cd and Co.The adsorbability of Cd in highly concentrated chloride solution (>1 M) was less than 1 liter/kg, presumably because of the chloride complex formation. This effect increased with increasing pH. The low adsorbability of Cd on montmorillonite from concentrated NaCI solution is promising with respect to its use as a tracer for monitoring flow through formations containing montmorillonite.

No abstract