Russia-Battling Waterborne Contaminants with UV

Pediastrum, a member of the Kingdom Protista family of taxa. Photos: CH Diagnostic and consulting service Inc.

Summary: The effectiveness of UV for inactivating Cryptosporidium parvum and Giardia lamblia is well documented. Most studies focus on medium-pressure ultraviolet (UV). This article describes an investigation carried out in Russia using low-pressure UV systems.

Cryptosporidium parvum oocysts and Giardia lamblia cysts are waterborne parasites. Their resistance to the chlorine concentration normally used to treat water contributes to waterborne outbreaks of human disease.1,2 Monitoring of protozoa in surface water sources and drinking water carried out under the Research Institute of Medical Parasitology and Tropical Medicine (RIMPTM) in several regions of Russia showed that there's a high risk of waterborne disease. The protozoa cysts were detected in surface water in 56.8 percent of cases and 13 percent of cases in drinking water.3

Since the largest outbreak occurred in Milwaukee in 1993, protozoa control has become a primary focus of drinking water plants operators in the United States. The search for effective treatment showed that ultraviolet (UV) may be a viable solution to disinfecting Cryptosporidium. Animal infectivity assays have shown that UV disinfection at relatively low doses provides several logs of Cryptosporidium parvum inactivation.4,5 As a result, UV can be used as the best available technology (BAT) for protozoa control.

Sphercal bodies indicated with arrows are Cryptosporidium oocysts.

The research was undertaken to determine sufficient UV doses required from low-pressure lamps for inactivation cysts and oocysts in drinking water, surface water and wastewater. The ability of UV to inactivate protozoa has been examined by in vivo mouse infectivity assays.6 The assays were carried out under the auspices of RIMPTM. A laboratory UV apparatus and UV systems installed at water treatment plants in the Russian cities of Toglliatti and Otradniy were used for the studies. All UV equipment had mercury low-pressure lamps that emitted UV at a germicidal wavelength of 254 nanometers (nm).

Bench laboratory experiments

The bench laboratory studies included experiments with synthetic model water and wastewater. The synthetic model water was prepared using 400 milliliters (ml) of dechlorinated drinking water (Nephelometric Turbidity Unit, or NTU < (NOTE: misprint) 1) and 1 ml maximum purified suspension of viable Cryptosporidium parvum oocysts. Oocysts were enumerated to provide concentrations-100 and 1,000 oocysts (with 5 percent deviation to one side or another) in 1 ml of the suspension.

Water inoculated with protozoa oocysts was exposed by UV radiation (UV doses of 16, 40 and 80 milliJoules per centimeter squared, mJ/cm2) and, after centrifugation, was given to laboratory mice. Non-UV treated water was given to different mice as a control of viability of non disinfected protozoa. Three mice were used for each control sample and five mice for each UV-treated sample. All experiments were conducted three times. Results of these studies are shown in Table 1.

Table 1. Results of bench laboratory studies with synthetic model water

All control animals were infected. In experiments with initial concentration of pathogens (1 102 oocysts per 1 ml), all UV doses provided total inactivation of Cryptosporidium parvum oocysts. Experiments with initial concentration of oocyts 1 103 per 1 ml, showed that a UV dose of 16 mJ/cm2 provided effectiveness of disinfection in at least 67 percent of cases and UV doses of 40 and 80 mJ/cm2 provided total inactivation in all cases. The results estimated a >2-log inactivation at 16 mJ/cm2 and > (NOTE: it was a misprint) 3-log inactivation at 40 and 80 mJ/cm2. During the next step of the bench laboratory studies, samples of wastewater were treated by UV (doses of 20, 30 and 40 mJ/cm2) and examined by in vivo mouse infectivety. The attributes of biologically treated wastewater used in the experiments are shown in Table 2. The results of mouse infectivety assays are shown in Table 3.

Table 2. Quality of wastewater used in bench laboratory studies

Table 3. Results of bench laboratory studies with wastewater

Mouse infectivity assays determined that a UV dose of 20 mJ/cm2 slightly reduced protozoa infectivity (10 of 15 mice were infected) in wastewater. Meanwhile, a UV dose of 30 mJ/cm2 reduced protozoa infectivity from 100 percent to 20 percent (three of 15 mice were infected by Cryptosporidium). No infection was detected after treating wastewater with a UV dose of 40mJ/cm2.

Initial quantity of protozoa in wastewater wasn't determined. Therefore, it was impossible to determine log inactivation. Nevertheless, the studies demonstrated a principal ability to disinfect protozoa cycts and oocysts by low-pressure UV in wastewater.

UV plants' monitoring

Protozoa monitoring was conducted at the surface water treatment plants in Otradniy and Tolyatty. Both plants use low-pressure UV systems for the first step of treatment. The water treatment plants have similar water treatment schemes (see Figure 1) and different sources of water. Main features of the water sources and UV systems are shown in Table 4.

Table 4. Quality of surface source water used in bench laboratory studies

Samples were taken before (from surface water) and after UV disinfection as well as a drinking water reservoir. The volume of samples were 30 liters (L) for surface water and 50 L of UV-treated water for drinking water. Protozoa infectivity was assessed in vitro and in vivo assays. Three mice were used in each sample. The study lasted from from September 2000 until June 2001. During this period, 26 samples were investigated.

Water sources of these plants are different one from another in respect to bacterial pollution. At the same time, the quantity of protozoa is approximately equal in both water sources. Cysts and oocysts of protozoa were detected in each examined sample from surface water-the number of Giardia lamblia cysts went from four to 26 and the number of Cryptosporidium parvum oocysts increased from four to 52. One to three mice were infected in each sample from the surface water. In vitro assays of UV-treated water have shown that the number of protozoa was reduced. Anywhere from zero to seven cysts and oocysts were detected in these samples. At the same time, animal infectivity assays indicated that UV systems provided a highly effective inactivation of protozoa-only one mouse was infected from 30 that were used in these experiments. Sampling during an April flood showed an absence of infection by all mice used in the experiment. In the samples from drinking water reservoirs, the cysts or oocysts weren't discovered via in vivo and in vitro assays.

Conclusion

Low-pressure UV light appears to be highly effective for inactivating protozoa cysts and oocysts in drinking water, surface water and wastewater. The last one is important as wastewater is the main source of surface water contamination in Russia. In short, effective inactivation of Cryptosporidium parvum and Giardia lamblia can be achieved by a UV dose that's not less than 16 mJ/cm2 in surface water and drinking water, and not less than 40 mJ/cm2 in wastewater.

Acknowledgments

The authors would like to thank The Research Institute of Medical Parasitology and Tropical Medicine and the surface water plant operators in Toglliatti and Otradniy.

References

1. Solo-Gabriele, H. and S. Neumeister. US outbreaks of cryptosporidiosis. J. AWWA. 88:76-86., 1996
2. MacKenzie, W.R., et al., "A Massive Outbreak in Milwaukee of Cryptosporidium Infection Transmitted Through the Public Water Supply," New England Journal of Medicine, 331(3):161, 1994.
3. Romanenko, N.A., I.K. Padchenco, and Chebishev N.V., "Sanitary Parasitology: gaudiness for doctors," 2000.
4. Campbell A.T., "Inactivation of oocyst Cryptosporidium parvum by ultraviolet radiation" // Water Res., 1995, 29:2583
5. Bukhary, Z., et al., "Medium-pressure UV for oocysts inactivation," Journal of American Water Works Association, 91:3:86, 1999.
6. "Laboratory diagnostics of Cryptosporidium," Leningrad, p. 21, 1987.

About the authors

Sergey V. Volkov is the head of sales and marketing department at LIT Technology, a company that engineers and manufactures UV disinfection systems. He has over 20 years of experience in the field of water and wastewater engineering

Dr. Alexander V. Krasnochub is technical director of LIT Tehnology. He holds over 10 patents associated with UV technology. He can be reached at chub@npo.lit.ru

Alexander V. Yakimenko is the sales manager of UV systems at LIT Technology. He's written over 20 articles related to the water tratment industry.

Svetlana G. Zaitseva is technology department manager with responsibility for micribiological testing. She can be reached at email: svetlana_zaiceva@mail.ru
All of the authores can be contacted at +7 095 733-95-26, email: lit@npo.lit.ru