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Machine Description and Full Scale Test Results
A new water disinfection system has been developed to inactivate Cryptosporidium oocysts and Giardia cysts in drinking water. The technology, known as the CID, inactivates these pathogenic waterborne microorganisms using enhanced ultraviolet (UV) irradiation technology without filtrate disposal, chemical addition or related hazardous by-products.
To verify the effectiveness of the new technology, live challenge testing and infectivity studies were commissioned by Safe Water Solutions L.L.C. (SWS) of Brown Deer, Wisconsin. The live challenge tests were conducted by Clancy Environmental Consultants, Inc. (CEC) of Saint Albans, Vermont. Infectivity studies were conducted by the University of Arizona, College of Agriculture, Department of Veterinary Science in Tucson, Arizona.
The largest outbreak to date is the 1993 episode in Milwaukee, Wisconsin, where 403,000 people were infected with the disease and scores of people died from it. Cryptosporidium is found in 85 percent of all surface water sources and approximately 25 percent of all filtered finish waters (1). It has also been identified in ground water under the influence of surface water. Cryptosporidium is, as an oocyst, an ovoid-shaped
hard-shelled parasite measuring from between 3p;7 microns in diameter. It can pass through a well-operated water treatment plant with turbidity of less than 0.1 NTU and is highly resistant to conventional disinfection technologies. This can be a special concern to firms that use non-pasteurized water in the preparation of food and beverage products.
The dose of UV irradiation required to disinfect (inactivate microorganisms) varies with the organism. Most bacteria can be inactivated (3 log kill) with a UV dose of between 25p;50 mWs/cm2 compared with Cryptosporidium oocysts which require a minimum of between 315p;378 mWs/cm2. The equipment in this study doses the microorganisms at approximately 20p;25 times the minimum dose for inactivating Cryptosporidium, i.e. > 8,000 mWs/cm2.
Water flow through the unit is continuous. It flows through the screen in chamber 1, microorganisms are trapped on the screen and irradiated by the three UV lamps. The flowing water passes from chamber 1 into chamber 2 where an identical screen is located. After the pre-set dosage of 4,000 mWs/cm2 (about five minutes) is achieved, a series of valves is automatically operated-reversing the flow. Any microorganisms trapped on the screen in chamber 1 are flushed off of that screen and onto the screen in chamber 2 where they receive a second irradiation dosage of 4,000 mWs/cm2. After
this dosage is achieved, the valves reverse again sending the inactivated microorganisms out of the machine. All microorganisms receive two doses at 4,000 mWs/cm2 each. See Figure 1.
Two live challenge tests were conducted. Each test had a spike of 5 x 108 live Cryptosporidium oocysts. The two spikes, along with a transport control specimen, were obtained from the University of Arizona. Since the machine is designed such that UV dosage/inactivation is independent of flow rate, two different flow rates were selected for the live challenges.
For each test, all water that passed through the machine was filtered to capture the treated oocysts (1 micron absolute filters).
For each challenge, the oocyst spike was pumped into the machine over one five-minute cycle followed by two "pump purges" over two additional cycles. The initial test was run at a water flow rate of 125 gpm. The machine was cycled six times, the water flow was stopped and the oocyst capture filters were removed and prepared for transport to the laboratory. New capture filters were installed and the water flow rate was adjusted to
62 gpm. A second spike of 5 x 108 live oocysts was pumped into the system as described earlier. After six complete cycles, the flow to the machine was stopped, the capture filters were removed and prepared for transport to the CEC laboratory.
The filter cartridges and control oocysts were hand-delivered to the laboratory the following day. The treated oocysts recovered from the filters along with the live control oocysts were sent to the University of Arizona, College of Agriculture, Department of Veterinary Science for the live infectivity studies.
The results of the infectivity tests of the treated oocysts, from both challenge tests, showed that no animals were infected. These results indicate a greater than 3 log reduction/inactivation (> 99.9 percent) due to the treatment achieved with the CID technology-independent of flow rate.
About the Author:
G. Michael Furst, Jr., P.E., is product manager for Safe Water Solutions L.L.C., Brown Deer, Wisconsin.