Stephen A. Craik

Inactivation of cryptosporidium parvum oocysts using medium- and low-pressure ultraviolet radiation

The effect of ultraviolet radiation from low- and medium-pressure mercury arc lamps on Cryptosporidium parvum oocysts was studied using a collimated beam apparatus. Experiments were conducted using parasites suspended in both filtered surface water and phosphate buffered laboratory water. Inactivation of oocysts was measured as reduction in infectivity using a CD-1 neonatal mouse model and was found to be a non-linear function of UV dose over the range of germicidal doses tested (0.8-119 mJ/cm2). Oocyst inactivation increased rapidly with UV dose at doses less than 25 mJ/cm2 with two and three log-units inactivation at approximately 10 and 25 mJ/cm2, respectively. The cause of significant leveling-off and tailing in the UV inactivation curve at higher doses was not determined. Maximum measured oocyst inactivation ranged from 3.4 to greater than 4.9 log-units and was dependent on different batches of parasites. Water type and temperature, the concentration of oocysts in the suspension, and the UV irradiance did not have significant impacts on oocyst inactivation. When compared on the basis of germicidal UV dose, the oocysts were equally sensitive to low- and medium-pressure UV radiation. With respect to Cryptosporidium, both low- and medium-pressure ultraviolet radiation are attractive alternatives to conventional chemical disinfection methods in drinking water treatment.

Inactivation of Giardia muris cysts using medium-pressure ultraviolet radiation in filtered drinking water.

The effect of medium pressure ultraviolet radiation on Giardia muris was studied using a collimated beam apparatus with filtered surface water from the Grand River, Kitchener, Ontario, Canada. UV doses ranged from 5 to 83 mJ/cm2 and resulted in 2–3 log-units of reduction in infectivity measured by a C3H/HeN mouse infectivity model. In vitro excystation and nucleic acid staining with Live/Dead BacLight™ greatly underestimated the inactivation of Giardia when compared with animal infectivity. Medium pressure ultraviolet radiation is a potential alternative to conventional chemical disinfection methods.

Comparison of the action spectra and relative DNA absorbance spectra of microorganisms: information important for the determination of germicidal fluence (UV dose) in an ultraviolet disinfection of water.

The action spectra of Bacillus subtilis spores (ATCC6633) and Salmonella typhimurium LT2 were characterized using physical radiometry for irradiance measurements and a multiple target model to interpret the inactivation kinetics. The observed action spectrum of B. subtilis spores deviated significantly from the relative absorbance spectrum of the DNA purified from the spores, but matched quite well with the relative absorbance spectrum of decoated spores. The action spectrum of B. subtilis spores determined in this study was statistically different from those reported in previous studies. On the other hand, the action spectrum of S. typhimurium bacteria matched quite well with the relative absorbance spectrum of DNA extracted from vegetative cells, except in the region below 240nm. It is concluded that the common use of the relative DNA absorbance spectrum as a surrogate for the germicidal action spectrum can result in systematic errors when evaluating the performance of a polychromatic UV light reactors using bioassays. For example, if the weighted germicidal fluence (UV dose) calculated using the relative DNA absorbance spectrum as the germicidal weighting factor is found to be 40mJcm(-2) for a medium pressure lamp UV reactor, that calculated using the relative action spectrum of B. subtilis spores, as determined in this study, would be 66mJcm(-2).

Assessment of human virus removal during municipal wastewater treatment in Edmonton, Canada

To assess the removal of viruses through the multiple steps of wastewater treatment in a full‐scale municipal wastewater treatment plant in Alberta, Canada.

Pre-analytical and analytical procedures for the detection of enteric viruses and enterovirus in water samples

Practical pre-analytical and analytical procedures were developed and validated for detection of enteric viruses in three water matrices. Both RNA viruses (norovirus, coxsackievirus, echovirus, and rotavirus) and DNA virus (adenovirus 41) were included in the study. The NanoCeram 90mm laminated disc with electropositive filter and procedures of filtration, elution and flocculation were utilized to concentrate known amount of viruses in different water matrices. Real time quantitative PCR was used to evaluate the recovery of virus and cell culture to assess viral infectivity. There was no PCR inhibition using various concentrations and pH of beef extract eluting buffer. A good recovery of the viruses spiked in 10L of deionized water was achieved for serial dilutions of coxsackievirus (41-67%), echovirus (22-90%), norovirus (23-44%) and rotavirus (24-46%). Relatively lower recovery was observed for adenovirus 41 (24-35%). There was no significant difference in viral recovery from deionized, tap and river water samples. The infectivity of recovered adenovirus, coxsackievirus and echovirus was demonstrated using in vitro cell culture. The pre-analytical and analytic procedures attained consistent recovery of RNA and DNA viruses both as infectious viral particles and viral genome, provided effective removal of inhibitory substances, achieved reliable reproducibility, and were relatively inexpensive for monitoring viruses in water.

Infectivity of Giardia lamblia cysts obtained from wastewater treated with ultraviolet light

Several waterborne outbreaks of giardiasis have been linked to discharge of wastewater effluents into surface water. Little is known about the infectivity of Giardia lamblia cysts present in UV treated wastewater effluents. In this study, the infectivity of G. lamblia cysts, recovered from primary effluent and secondary effluent, both upstream and downstream of operating full-scale UV reactors at four wastewater treatment plants, was assessed using the Mongolian gerbil model. Infectivity of cysts obtained from the primary effluents was scored as either strong or moderate for induction of infection in gerbils at three out of four wastewater treatment plants. G. lamblia recovered from secondary effluent both upstream and downstream of the UV reactors caused weak infections in the gerbils. The probability of weak infections caused by inoculums of 50-1400 cysts per gerbil was, on the average, reduced by approximately 10% at the four wastewater UV installations with coliform reduction equivalent doses ranging from 6 to 18 mJ/cm2. The UV systems provided considerably less inactivation of the parasite than expected based on the UV dose response of Giardia reported in the literature.

Synergistic inactivation of Cryptosporidium parvum using ozone followed by free chlorine in natural water.

The synergistic effect of sequential exposure to ozone followed by free chlorine on inactivation of Cryptosporidium parvum oocysts suspended in natural waters was studied in bench-scale batch reactors. Animal infectivity using neonatal CD-1 mice was used to measure oocyst inactivation. The synergistic effect measured in two alkaline (pH 8.1) natural waters was statistically significant but was considerably smaller than previously reported in buffered de-ionized water at pH 6.0. Temperature, ozone primary treatment level, and water type did not have measurable impacts on the synergistic effect. Efforts to increase the synergistic effect by reducing the pH from 8 to 6 by acid addition were unsuccessful. In the two low alkalinity (pH 6.0) natural waters tested, the measured synergistic effect was greater than in the alkaline waters, but was still less than that measured previously in buffered de-ionized water. It was concluded that the synergistic effect reduction in the natural waters tested was due in part to alkalinity and in part to other unidentified water quality characteristics. Sequential treatment with ozone followed by free chlorine may only be a feasible strategy for achieving synergistic C. parvum inactivation credit for water treatment facilities with natural waters having a low pH (near 6.0).

The assessment of particle association and UV disinfection of wastewater using indigenous spore-forming bacteria.

Studies have shown that association between particles and coliform bacteria in wastewater influence the inactivation of these microorganisms by ultraviolet (UV) irradiation. This research investigated the potential use of indigenous aerobic spore-forming (ASF) bacteria for studying the particle - microorganism interaction and its effect on UV disinfection of protozoan pathogens, such as Giardia spp. and Cryptosporidium spp., present in effluents from full-scale municipal wastewater treatment plants. The effect of particle - ASF association was determined by homogenizing wastewater effluent samples before and after exposure to controlled UV doses delivered by a bench-scale collimated beam apparatus. Particle association between Bacillus subtilis spores added to wastewater and wastewater particles was also assessed. The results indicate that spores are not significantly associated with wastewater particulate matter and particle association does not significantly affect the inactivation of indigenous spores present in wastewater by UV radiation in this study.

Comparison of levels of inactivation of two isolates of Giardia lamblia cysts by UV light.

ABSTRACT The effects of 254-nm UV irradiation on two human isolates (WB and H3) of Giardia lamblia cysts were assessed using a collimated beam protocol and a Mongolian gerbil model. The levels of infection of cysts in the gerbils were assessed based on the presence of cysts in feces and the presence and activity of trophozoites in the small intestine of inoculated gerbils. The results suggest that there were differences in the infectivities of the WB and H3 isolates, as well as in susceptibilities of the parasites to UV light. Without UV exposure, gerbils were more readily infected by isolate H3 cysts. After UV exposure of the cysts, however, the gerbils were more susceptible to isolate WB cysts.

Effect of turbulent gas-liquid contact in a static mixer on Cryptosporidium parvum oocyst inactivation by ozone.

Static mixers may be used to dissolve gaseous ozone in water treatment facilities in order to provide protection against the waterborne parasite Cryptosporidium parvum. The objective of this study was to determine the effect of a brief exposure to turbulent gas-liquid mixing conditions in a static mixer on inactivation of C. parvum oocysts by ozone. Inactivation measured in an ozone contacting apparatus that employed a static mixer for ozone dissolution was compared to predictions based on a previously published kinetic model of C. parvum inactivation by dissolved ozone in gently stirred batch reactors. Although initial contact in the static mixer had no immediate effect on the oocysts, a 20% increase in the rate of inactivation during subsequent contact with dissolved ozone was observed. Increasing the degree of turbulence within the static mixer did not yield additional inactivation. Use of static mixers for dissolution of ozone in drinking water treatment systems may provide limited enhancement of C. parvum inactivation by dissolved ozone.