Search

In this study, we determined the removal of a prototype human norovirus (Norwalk virus, NV) by bench-scale alum coagulation, flocculation and sedimentation processes using reverse transcriptase polymerase chain reaction (RT-PCR) for norovirus assays. After determining optimum conditions for the coagulation, flocculation and sedimentation processes in terms of turbidity reduction, jar tests were performed using the same waters seeded with test viruses. For comparison, two other important health-related viruses, poliovirus 1 (PV1) and coliphage MS2, were included in this study. The removal of NV by coagulation, flocculation and sedimentation processes based on RT-PCR assay in this study was 1.5 log10, which was similar to that of PV1 and a little lower than that of coliphage MS2 (2 log10) based on the same RT-PCR assay. The removal of NV in this study (1.5 log10) is considerably higher than the one in a recent study using recombinant norovirus virus-like particles (∼0.7 log10). Overall, the results of this study suggest that human noroviruses can be appreciably reduced by a properly-operated coagulation, flocculation and sedimentation processes and the contamination of drinking water by noroviruses should be controlled by conventional water treatment processes with conventional physico-chemical processes and disinfection.

Aims: In this study, we determined the ability of a promising alternative UV technology – a polychromatic emission from a medium-pressure UV (MP UV) technology – to inhibit the reactivation of UV-irradiated Giardia lamblia cysts. Methods and Results: A UV-collimated beam apparatus was used to expose shallow suspensions of purified G. lamblia cysts in PBS (pH 7·2) or filtered drinking water to a low dose (1 mJ cm−2) of MP UV irradiation. After UV irradiation, samples were exposed to two repair conditions (light or dark) and two temperature conditions (25°C or 37°C for 2–4 h). The inactivation of G. lamblia cysts by MP UV was very extensive, and c. 3 log10 inactivation was achieved with a dose of 1 mJ cm−2. Meanwhile, there was no apparent reactivation (neither in vivo nor in vitro) of UV-irradiated G. lamblia under the conditions tested. Conclusion: The results of this study indicated that, unlike the traditional low-pressure (LP) UV technology, an alternative UV technology (MP UV) could inhibit the reactivation of UV-irradiated G. lamblia cysts even when the cysts were exposed to low UV doses. Significance and Impact of the Study: It appears that alternative UV technology has some advantages over the traditional LP UV technology in drinking water disinfection because of their high level of inactivation against G. lamblia cysts and also effective inhibition of reactivation in UV-irradiated G. lamblia cysts.

In an effort to validate previous research suggesting remarkable resistance of norovirus to free chlorine disinfection, we characterized the disinfection response of purified and dispersed Norwalk virus (NV) by bench-scale free chlorine disinfection using RT-PCR for virus assays. The inactivation of NV by two doses of free chlorine (1 and 5mg/L) at pH 6 and 5 degrees C based on two RT-PCR assays was similar to that of coliphage MS2, but much faster than that of poliovirus 1. Despite the underestimation of virus inactivation by RT-PCR assays, the predicted CT values for NV based on RT-PCR assays are lower than the ones for most other important waterborne viruses and the CT guidelines for chlorine disinfection of viruses under the Surface Water Treatment Rule by the United States Environmental Protection Agency. Overall, the results of this study indicate that NV is not highly resistant to free chlorine disinfection as suggested by previous research and it is likely that NV contamination of drinking water can be controlled by adequate free chlorine disinfection practices with provision of proper pre-treatment processes before chlorination.

In this study, we determined the repair capabilities of Giardia lamblia cysts when they were exposed to low-pressure (LP) UV and then 4 different repair conditions. A UV collimated beam apparatus was used to expose shallow suspensions of G. lamblia cysts in buffered reagent water (PBS, pH 7.2) to various doses of LP UV irradiation. After UV irradiation, samples were exposed to 4 repair conditions (light and dark repair conditions with 2 temperatures (25 °C and 37 °C) for each condition). The inactivation of G. lamblia cysts by LP UV was very extensive (∼5 log10) even with a low dose of LP UV (1 mJ/cm2). More importantly, there was significant restoration of infectivity in G. lamblia cysts when they were exposed to a low dose of LP UV and then to all the repair conditions tested. Overall, the results of this study indicate that G. lamblia cysts do have the ability to repair their UV-damaged DNA when they are exposed to low doses of LP UV irradiation. This is the first study to report the presence of repair in UV-irradiated G. lamblia cysts.

To elucidate the roles of physical and chemical properties of viruses and their sensitivity to UV radiation, the kinetics and extent of inactivation of several waterborne pathogenic viruses and bacteriophages with different virion sizes and genomic composition by monochromatic, low-pressure (LP) UV was determined in phosphate buffered saline or a filtered drinking water. The inactivation rates of the small RNA viruses, poliovirus 1 and Coxsackievirus B4, by LP UV were very rapid and reached ~4 log10 and >5 log10, respectively, within a UV dose of 30 mJ/cm2. In contrast, the inactivation of the small RNA bacteriophage, MS2, was much slower and only 2 log10 inactivation was achieved at a UV dose of 30 mJ/cm2. The inactivation of the large DNA virus, adenovirus 2, was relatively slow and only 2 log10 inactivation was achieved with a UV dose of 60 mJ/cm2. In contrast, the inactivation rates of the three large DNA bacteriophages were very rapid and reached >5 log10 with a UV dose of 10 mJ/cm2. Therefore, the results of this study indicate that inactivation of human enteric viruses and bacteriophages by UV irradiation is not simply predictable by the type and size of the virus or its nucleic acid genome and there is no strong correlation between virion size and genetic composition of enteric viruses and their response to LP UV irradiation. Key words: low pressure ultraviolet (LP UV), poliovirus 1, Coxsackievirus B4, bacteriophage MS2, bacteriophage PRD1, adenovirus 2, UV disinfection.

The Greater Cincinnati (Ohio) Water Works strives to continually improve the effectiveness of its water treatment processes. Questions regarding the vulnerability of the Ohio River watershed to microbial contamination and concerns about compliance with the Long Term 2 Enhanced Surface Water Treatment Rule led the utility to initiate an in-depth study of ultraviolet (UV) disinfection. The study was designed to determine how exposing treated Ohio River water to UV affected (1) the inactivation of Cryptosporidium parvum, bacteria, and viruses, (2) the susceptibility of these microorganisms to free chlorine after partial inactivation with UV, (3) the formation of oxidation and chlorinated disinfection by-products (DBPs), and (4) microbial regrowth (measured by assimilated organic carbon) following UV disinfection. Results indicated that UV alone or UV followed by free chlorine effectively controlled all microorganisms tested. Additionally, no evidence of increased DBP formation or regrowth was observed at UV doses typically used for disinfection.

Norwalk virus and other human caliciviruses (noroviruses) are major agents of gastroenteritis, and water is a major route of their transmission. In an effort to control Norwalk virus in drinking water, Norwalk virus reduction by bench-scale ozone disinfection was determined using quantitative reverse transcription (RT)-PCR for virus assays. Two other enteric viruses, poliovirus 1 and coliphage MS2, were included for comparison, and their reductions were assayed by infectivity assays as well as by RT-PCR. Virus reductions by ozone were determined using a dose of 0.37 mg of ozone/liter at pH 7 and 5°C for up to 5 min. Based on two RT-PCR assays, the reductions of Norwalk virus were >3 log 10 within a contact time of 10 s, and these were similar to the reductions of the other two viruses determined by the same assay methods. Also, the virus reductions detected by RT-PCR assays were similar to those detected by infectivity assays, indicating that the RT-PCR assay is a reliable surrogate assay for both culturable and nonculturable viruses disinfected with ozone. Overall, the results of this study indicate that Norwalk virus as well as other enteric viruses can be reduced rapidly and extensively by ozone disinfection and that RT-PCR is a useful surrogate assay for both culturable and nonculturable viruses disinfected with ozone.

Cryptosporidium parvum oocysts in water were exposed to distinct wavelength bands of collimated beam ultraviolet (UV) radiation across the germicidal UV wavelength range (210-295 nm) that were emitted from a medium pressure (MP) mercury vapour lamp. The dose of UV radiation transmitted though each narrow bandpass filter was measured utilising potassium ferrioxalate actinometry. Oocyst infectivity was determined using a cell culture assay and titre was expressed as an MPN. The log10 inactivation for each band of radiation was determined for a dose of 2 mJ/cm2. Doses from all wavelengths between 250-275 nm resulted in approximately 2 log10 inactivation of Cryptosporidium parvum oocyst infectivity while doses with wavelengths higher and lower than this range were less effective. Because polychromatic radiation from MP UV lamps had about the same germicidal activity between the wavelengths of 250-275 nm for inactivation of oocyst infectivity, there was no unique advantage of MP UV over low pressure (LP) UV except for the simultaneous delivery of a wide range of germicidal wavelengths.

In an effort to reduce human exposure to adenoviruses through drinking water, we determined the effectiveness of sequential disinfection with an alternative ultraviolet (UV) technology (medium-pressure (MP) UV) and monochloramine. The results of this study showed that MP UV was much more effective than traditional UV technology (low-pressure (LP) UV) against human adenovirus 2 (Ad2). Specifically, an inactivation of ~3 log10 was achieved by a dose of 40 mJ/cm2 of MP UV compared to ~1 log10 by the same dose of LP UV. However, because of the ineffective inactivation of Ad2 by monochloramine, a very high dose (40 mJ/cm2) of MP UV and a very large Ct99 value (~1200 mg/L·min) was still needed to achieve a significant inactivation (e.g., 4 log10) of Ad2. Also, it appears that the inactivation of Ad2 by monochloramine is not enhanced by prior exposure to MP UV. Overall, the results of this study indicated that, in spite of the enhanced effectiveness of alternative UV technologies on human adenoviruses, sequential disinfection with an alternative UV technology (MP UV) and monochloramine still may not provide adequate inactivation of human adenoviruses — especially at high pH and low temperature — in drinking water treatment processes.

There has been growing concern over human exposure to adenoviruses through drinking water due to their apparent high resistance to UV irradiation and the anticipated widespread use of ultraviolet (UV) disinfection in drinking water treatment processes. However, most inactivation studies on adenoviruses were performed using only one type of UV technology—low-pressure (LP) UV, and little is known about the effectiveness of different UV technologies such as medium- pressure (MP) UV or other polychromatic UV technologies. In this work, the kinetics and extent of inactivation of a human adenovirus (adenovirus 2 (Ad2)) by both monochromatic LP and polychromatic MP UV were evaluated to determine the effectiveness of these UV technologies on human adenoviruses. Inactivation of Ad2 by LP UV was very slow and only 0.87 and 2.17 log10 inactivation was achieved with UV doses of 30 and 90 mJ/cm2, respectively. However, inactivation of Ad2 by MP UV was much faster and 2.19 and 5.36 log10 inactivation was observed with the same UV doses (30 and 90 mJ/cm2, respectively). It appears that MP UV is more effective against Ad2 than LP UV and the enhanced effectiveness of MP UV on Ad2 is likely due to its ability to inhibit the repair process in UV-irradiated Ad2.

Aims: Giardia lamblia is one of the most important waterborne pathogens in the world. In this study, we determined the effectiveness of a promising alternative UV technology – a polychromatic emission from a medium-pressure (MP) UV lamp – against G. lamblia cysts in phosphate buffered saline (PBS) and a filtered drinking water. Methods and Results: A UV collimated beam apparatus was used to expose shallow suspensions of purified G. lamblia cysts in PBS or a filtered drinking water and the UV-irradiated G. lamblia cysts were assayed in Mongolian gerbils. The inactivation of G. lamblia cysts was very rapid and reached a detection limit of >3 log10 within a UV dose of 1 mJ cm−2. Conclusion: The results of this study indicate that MP UV irradiation is very effective against G. lamblia cysts in both PBS and a filtered drinking water. Significance and Impact of the Study: It is likely that contamination of drinking water by G. lamblia cysts can be readily controlled by typical MP UV disinfection practises.

The human and animal pathogen Giardia lamblia is a waterborne risk to public health because the cysts are ubiquitous and persistent in water and wastewater, not completely removed by physical-chemical treatment processes, and relatively resistant to chemical disinfection. Given the recently recognized efficacy of UV irradiation against Cryptosporidium parvum oocysts, the inactivation of G. lamblia cysts in buffered saline water at pH 7.3 and room temperature by near monochromatic (254 nm) UV irradiation from low-pressure mercury vapor lamps was determined using a "collimated beam" exposure system. Reduction of G. lamblia infectivity for gerbils was very rapid and extensive, reaching a detection limit of4 log within a dose of 10 JM-2. The ability of UV-irradiated G. lamblia cysts to repair UV-induced damage following typical drinking water and wastewater doses of 160 and 400 JM(-2) was also investigated using experimental protocols typical for bacterial and eucaryotic DNA repair under both light and dark conditions. The infectivity reduction of G. lamblia cysts at these UV doses remained unchanged after exposure to repair conditions. Therefore, no phenotypic evidence of either light or dark repair of DNA damage caused by LP UV irradiation of cysts was observed at the UV doses tested. We conclude that UV disinfection at practical doses achieves appreciable (much greater than 4 log) inactivation of G. lamblia cysts in water with no evidence of DNA repair leading to infectivity reactivation.

The reduction of Norwalk virus (NV) by a 2 mg/L dose of pre-formed monochloramine was determined at pH 8 and 5°C in bench-scale, batch disinfection experiments using quantitative RT-PCR for NV assays. Two other enteric viruses, poliovirus 1 (PV1) and coliphage MS2, were included for comparison and assayed by infectivity as well as RT-PCR. After 3h, reductions of PV1 and MS2 by infectivity assays were about 1 log 10 but there were no reductions of these viruses by RT-PCR assays. Hence, RT-PCR underestimated virus inactivation by monochloramine. However, NV reduction by monochloramine was about 1 log 10 by RT-PCR assay, suggesting that it is more susceptible to monochloramine than the other two viruses tested. Based on RT-PCR titre reduction, the CT 99 value for NV was about 775 mg-min/L. If the reduction of NV infectivity by monochloramine is ever greater than the reduction of RT-PCR signals, the CT 99 value would be smaller. However, the results of this study indicate that NV and the other enteric viruses tested are not rapidly and extensively reduced by disinfection with pre-formed monochloramine.

Nucleic acid (NA) amplification techniques are useful to detect viruses in water and other environmental samples because they are highly sensitive, specific and can detect fastidious enteric viruses that do not grow well or not at all in cell cultures. However, RT-PCR was found to detect inactivated viruses. In terms of risks to public health this constitutes a false positive result, as inactivated viruses are no longer infectious. When poliovirus type 1 and coliphage MS2 were studied for (a) persistence in water and sewage and (b) inactivation in water by free chlorine, chlorine dioxide and UV radiation, RT-PCR assays underestimated virus inactivation. The use of multiple RT-PCR amplification sites, larger RT-PCR genomic targets and immunocapture RT-PCR sometimes reduced, but did not eliminate, the discrepancy between loss of infectivity and loss of RT-PCR titre. Virus presence based on RT-PCR detection must be interpreted with caution when predicting human health risks.