Abstract: Conventional lab water systems use UV light by flowing water in a chamber around the bulb in a protective quartz sleeve as part of the recirculation loop. Using innovative technologies, the UV light benefits are maximized but sterilizing the water in the loop and the dispensing port as well.
Introduction: For many years, the water industry has known the many benefits of ultraviolet (UV) light for germicidal reduction. The specific wavelength of 254 nm destroys the nucleic acids of the bacteria’s DNA rendering it sterilized and prevents the colony from growing.
In most lab water systems today, UV systems are installed as a single pass within the recirculating loop. Water flows around a UV bulb in a quartz sleeve sterilizing the purified water. To dispense the water, an automated or manual valve is opened and flow will enter a 0.2 micron capsule filter upon exit. As the system sits idle, a potential for bacteria growth exist on areas outside of the recirculating loop: post valve tubing and submicron filter. Most manufactures recommend flushing water through the filter before use to purge the small standing water. To bring awareness of this potential issue, ASTM 5196 Biomedical grade specification, Section 4.5 addresses the dispensing port:
The distribution outlets or faucets must be of non-contaminating design and materials. Particular care must be given to the valve seat and joint construction. The outlet must be protected from biological contamination particularly when the use is only occasional. Ultraviolet (UV), chemical, or heat sterilization should be considered.
An innovative approach for UV sterilization has been developed to irradiate the water at multiple passes within the recirculating loop. By taking a UV bulb in an atmospheric, shielded box, Teflon coiled tubing wraps around the UV bulb with a turbulent flow and maximizing surface area irradiation. Water is UV irradiated before deionization, after DI and submicron filtration, and the outlet dispensing port thus meeting the ASTM 5196 specification for Biomedical Grade Water. The Aries Filteworks Gemini system with multi-pass UV was tested with a bacteria challenge.
Experiential Conditions: A pure strain of Pseudomonas aeruginosa was inoculated into a flask and incubated for 24 hours. Following incubation, enumeration was performed using diluted spread plate technique. The culture was determined to contain 2.0 x 109 cultivable bacteria per ml using Pseudomonas Isolation Agar (PIA).
Following introduction of the challenge organisms, the Gemini was allowed to recirculate for one minute. After recirculation, three samples were dispensed from the Gemini outlet and collected in 1 liter autoclaved bottles. This procedure was repeated for samples collected at 30 minute and 1, 2, 3, 4, 24 and 48 hour post spike injections. No other water was dispensed form the Gemini unit during the test period. Following incubation for 24 hours and five days, bacteria on the plates were enumerated. The Gemini panel resistivity meter reading was noted and the dispensing UV lamp was checked at each sampling.
Results: During the test period, the Gemini resistivity was equal to or greater than 18.1 meghomn-cm @ 250 C. The UV lamp at the dispenser port was operating during each sample event. No viable bacteria were discovered from any of the triplicate 1 liter Gemini outlet samples collected 0 to 48 hours following a P.Aeruginosa spike
Samples collected twenty eight days after the spiking of the Gemini feed water with 2x1010 Pseudomonas aeruginosa bacteria cells and analyzed by the Kinetic Turbidimetric Method, was also completed for pyrogens with less than 0.003 EU/mL
Conclusions: Using the non-conventional methods of UV sterilization in a multi-pass arrangement provides the user with confidence that the dispensing port has not been compromised with bacteria growth. The Gemini ultrapure water system use of UV, deionization, and submicron filtration provides consistent, reliable Type I and Biomedical grade water.
References: ASTM D5196 - 06 Standard Guide for Biomedical Grade Water