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.
Waterborne disease is a concern in the United States and throughout the world. The World Health Organization cites that 8,500 people die each day from waterborne disease-80 percent of these deaths are children under the age of five years. Disease outbreaks are not exclusive to underdeveloped countries. In 1976, the first case of cryptosporidiosis was reported in humans. This disease is attributed to the parasite Cryptosporidium. Documented outbreaks of cryptosporidiosis have occurred in the United States since 1986.
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.
The unit CID-2S can treat a maximum of 440 gpm, and the unit CID-4S can treat flows up to 880 gpm. The machine has two treatment chambers. Each chamber is divided in half by a specially designed filter screen. The screen has nominal 2 micron openings. On each side of the screen are three sets of low pressure UV lamps. The lamps generate a 253.7 nm wavelength which is within the germicidal wavelength band of 250-270 nm. The lamps are enclosed
in Teflon-coated quartz sleeves to minimize fouling. Each of the sleeves has two lamps in it-one duty and one stand by. Three mercury vapor UV lamps are in operation in each section of the chamber at all times. Lamp operation (status) is continuously monitored and displayed on the control panel.
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.
Live Challenge Test
Since it is generally accepted that Cryptosporidium is more resistant to inactivation than is Giardia, Cryptosporidium was used for the challenge testing. Water for the test was taken from a municipal distribution system using Lake Michigan water as its source. The water was taken via hydrant to a 25,000 gallon steel tank and was pumped to the challenge test apparatus.
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.
Infectivity Test Results
The University laboratory tested oocyst viability using the BALB/c mouse model. The results of the testing indicated that the control oocysts were "very viable."
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.
The results of this testing support and go beyond earlier testing done by Campbell et al (3) at the Scottish Parasite Diagnostic Laboratory. The results of these tests are excellent, indicating that this innovative technology can be used now in potable water systems to inactivate Cryptosporidium and other waterborne pathogens.
- 1. LeChevallier, M.W., Norton W.D., and Lee R.G. (1991). Occurrence
of Giardia and Cryptosporidium in surface water supplies. Appl. Environ, Microbiol. 57:2610p;2616.
- 2. Clancy, J.L., W.D. Gollnitz, and Z. Tabib. 1994. Commercial labs: how accurate are they? J. American Water Works Assoc. 86:89p;97.
- 3. Campbell, A.T., L.J. Robertson, M.R. Snowball, and H.V. Smith. 1995. Inactivation of oocysts of Cryptosporidium parvum by ultraviolet irradiation. Water Research 29:283p;2586.
About the Author:
G. Michael Furst, Jr., P.E., is product manager for Safe Water Solutions L.L.C., Brown Deer, Wisconsin.