Volume 45 Number 2
World Spotlight: Russia—Battling Waterborne Contaminants with UV
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Summary: UV‘s effectiveness for inactivating Cryptosporidium parvum and Giardia lamblia is increasingly well documented. Most studies focus on medium-pressure 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 there’s a high risk of waterborne disease. The protozoa cysts and oocysts were detected in surface water in 56.8 percent and 13 percent of cases in drinking water, respectively.3
Since the largest Cryptosporidium 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 ultraviolet (UV) light may be a viable solution to disinfecting Cryptosporidium. Animal infectivity assays have shown UV disinfection at relatively low doses provides several logs of Cryptosporidium parvum inactivation.4,5 As a result, UV has been recognized by the U.S. Environmental Protection Agency (USEPA) as a significant tool for protozoa control that minimizes disinfection by-products. Guidelines for UV doses and log reduction requirements are being finalized now under the USEPA Long Term 2 Enhanced Surface Water Treatment Rule.
The research presented here was undertaken to determine sufficient UV doses required from low-pressure lamps for inactivation of 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 Toljatti 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).
The laboratory UV apparatus used is shown in Figure 1. This apparatus uses three low-pressure, 9-watt (W) mercury-arc UV lamps. Measurement of irradiation intensity is provided by photodetector. Mixing of water via magnets and magnetic stirrer provides equal irradiation of testing water. The volume of water was 400 milliliters (ml). The thickness of water layer was 4 centimeters (cm). UV doses were determined by varying time of exposure (from 4 to 18 minutes).
Bench lab experiments
Water inoculated with protozoa oocysts was exposed by UV radiation (UV doses of 16, 40 and 80 milliJoules per centimeter squared, mJ/cm2). After that testing, water was centrifuged three times to decrease volume from 400 ml to 1 ml. Invasive material was orally introduced to neonatal laboratory mice (0.2 ml for each mouse). Non-UV treated water passed the same procedure and 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. Seven days after inoculation, animal feces and samples of terminal ileum (the last part of the small intestine) were examined for Cryptosporidium parvum oocyst presence using staining by hemotxylin and eosin. All experiments were conducted three times. Results are shown in Table 1.
All control animals were infected. In experiments with initial concentration of pathogens (1x102 oocysts per 1 ml), all UV doses provided total inactivation of Cryptosporidium parvum oocysts. Experiments with initial concentration of oocyts 1x103 per 1 ml, showed a UV dose of 16 mJ/cm2 provided effectiveness of disinfection in at least 67 percent of cases and 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 >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 infectivity. The attributes of biologically treated wastewater used in the experiments are shown in Table 2. The results of mouse infectivity assays are shown in Table 3.
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 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
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. Samples were filtrated and centrifuged to reduce the volume from 30 or 50 L to 1 ml. Protozoa infectivity was assessed in vitro and in vivo assays. Three mice were used in each sample. The study lasted from September 2000 until June 2001. During this period, 26 samples were investigated.
Water sources of these plants are different from one 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 ranged from four to 26 and the number of Cryptosporidium parvum oocysts increased from four to 52 per volume of sample (30 L). 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 per 30 L were detected in these samples. At the same time, animal infectivity assays indicated UV systems provided a highly effective inactivation of protozoa—only one mouse was infected from 30 used in these experiments. Sampling during an April flood showed an absence of infection by all mice in the experiment. In the samples from drinking water reservoirs, cysts or oocysts weren’t discovered via in vivo nor in vitro assays.
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