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Microbial contamination of groundwater by viruses, bacteria, and parasitic protozoa is a significant human health problem when drinking water supplies are untreated or inadequately treated. The decision to treat groundwater supplies, if... more
Microbial contamination of groundwater by viruses, bacteria, and parasitic protozoa is a significant human health problem when drinking water supplies are untreated or inadequately treated. The decision to treat groundwater supplies, if sufficient resources are available, often depends on the adequacy of pathogen and indicator organism attenuation in the subsurface. Microbial fate and transport processes govern attenuation in the subsurface. Hence, a thorough understanding of the mechanisms and factors affecting the fate and transport of microbial contaminants in the subsurface environment is essential for the protection of public health from waterborne disease. First, the various sources and types of microbial contaminants found in the subsurface are presented. Sources of microbial contaminants may be zoogenic (e.g., wildlife) or anthropogenic (e.g., septic systems). Second, the surrogates and indicators most commonly used to assess microbial transport and fate in groundwater are discussed. These include pathogenic and nonpathogenic bacteria, bacteriophage, and microbe-sized microspheres. Next, the key processes governing microbial fate and transport are described. Microbial transport is mainly controlled by advection, whereas the key processes governing the fate of microorganisms are retention onto aquifer solid surfaces and inactivation (or survival) of the microbes. Groundwater chemistry and moisture content are identified as two of the main physicochemical factors that influence the retention and survival of microorganisms in the subsurface. Finally, the importance of linking this fundamental science to the development of appropriate public policy and land use strategy is highlighted.
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This article consolidates and updates available information on Cryptosporidium removal by filtration, with a focus on optimal and suboptimal filtration performance. Emphasis was placed on integrating various strategies for optimizing... more
This article consolidates and updates available information on Cryptosporidium removal by filtration, with a focus on optimal and suboptimal filtration performance. Emphasis was placed on integrating various strategies for optimizing filtration processes with the most current information regarding pathogen removal by filtration. As this review underscores, in response to regulations such as the Interim Enhanced Surface Water Treatment Rule (IESWTR) and the Long Term 2 ESWTR, there is a need to develop methods to compare the relative effectiveness of treatment alternatives and to understand the most significant operational effects on filter performance. In many cases, filters operated at or near optimal conditions can achieve in the vicinity of 3‐log (or better) removal of Cryptosporidium. Operational conditions such as coagulant upsets and end‐of‐run (early breakthrough) filtration may significantly decrease oocyst removal by drinking water filters, even when filter effluent turbidities are low (<0.3 ntu).
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Research Interests: Microbiology, Biology, Filtration, Medicine, Multidisciplinary, and 15 moreDrinking Water Treatment, Effect size, Parasite, Flocculation, Animals, Electrophoresis, Ozone, Operant Conditioning, Reproducibility of Results, Cryptosporidium, Coagulation, Floculation, Electrophoretic Mobility, Phosphate Buffer Saline, and Cryptosporidium parvum
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This investigation examined the removal of Cryptosporidium and several surrogates by granular medium filtration. The study focused on coagulation impacts on removals. Inactivated C. parvum oocysts and non-inactivated Bacillus subtilis... more
This investigation examined the removal of Cryptosporidium and several surrogates by granular medium filtration. The study focused on coagulation impacts on removals. Inactivated C. parvum oocysts and non-inactivated Bacillus subtilis were seeded in two pilot plants. The pilot plant locations were chosen to represent different coagulation regimes. Under optimized coagulation conditions (filter effluent turbidity < 0.1 NTU), approximately 5 log10 removal of Crypto. was obtained in one location, and approximately 3 log10 in the other. This difference is likely related at least in part to the difference in coagulation regimes. Suboptimal coagulation produced a substantial deterioration of Crypto. removal in both locations. The trends seen for Bacillus were generally similar to those observed for Crypto.. Although turbidity may be of value for assessing coagulation impacts on Crypto. removal, particle counts may be a more sensitive parameter in this regard.
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Research Interests: Materials Science, Glass, Filtration, Scanning Transmission Electron Microscopy, Medicine, and 15 moreMultidisciplinary, Surface Roughness, Environmental science and technology, Porosity, Computer Simulation, Diffusion, Colloids, Theoretical Models, Particle Size, Sewage, Surface Properties, Microspheres, Colloid, Surface Finish, and Particle Deposition
Pilot‐scale studies were performed to evaluate Cryptosporidium parvum oocyst removal by a dual‐media filter during optimized, end‐of‐run, and breakthrough operating conditions. Oocyst‐sized polystyrene microspheres were also evaluated as... more
Pilot‐scale studies were performed to evaluate Cryptosporidium parvum oocyst removal by a dual‐media filter during optimized, end‐of‐run, and breakthrough operating conditions. Oocyst‐sized polystyrene microspheres were also evaluated as surrogates for C. parvum removal by filtration. At optimal conditions, the pilot‐scale filter consistently achieved ~5‐log removal of C. parvum and microspheres. During end‐of‐run operation when filter effluent turbidity levels were &lt;0.1 ntu, median oocyst removals deteriorated to ~3 log. During early (0.1–0.3 ntu) and late (&gt;0.3 ntu) breakthrough, filtration oocyst removals deteriorated to ~2.1 and ~1.4 log, respectively. Microsphere removals by filtration were similar to oocyst removals during both stable and challenged operating periods, suggesting that microspheres are useful surrogates for investigating C. parvum removal.
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... Filter Operation Effects on Pathogen Prepared by: Peter M. Huck and Monica B. Emeiko NSERC Chair in Water Treatment, Department of ... mg/L polymer present) 191 Figure 7.12 Influent turbidity and coagulant dosages for full-scale... more
... Filter Operation Effects on Pathogen Prepared by: Peter M. Huck and Monica B. Emeiko NSERC Chair in Water Treatment, Department of ... mg/L polymer present) 191 Figure 7.12 Influent turbidity and coagulant dosages for full-scale testing at MWD's FE Weymouth filtration plant ...
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Pilot‐scale studies were conducted to determine if polystyrene microspheres are reasonable surrogates for Cryptosporidium parvum removal by filtration. Previously reported data from a conventional pilot plant using a high coagulant dose... more
Pilot‐scale studies were conducted to determine if polystyrene microspheres are reasonable surrogates for Cryptosporidium parvum removal by filtration. Previously reported data from a conventional pilot plant using a high coagulant dose optimized for combined total organic carbon and particle removal were contrasted with data from a pilot‐scale, in‐line filtration plant using a low coagulant dose optimized for particle removal. The removal of oocysts and microspheres was investigated during optimal operation as well as periods of process challenge and ranged from 0.5 log to &gt;5 logs. When data over a wide range of operating conditions (and oocyst and microsphere removals) were available, approximately linear relationships were discerned (the coefficient of determination [R2] ranged from 0.74 to 0.96). Although the exact relationship between oocyst and microsphere removals by filtration was somewhat site‐specific, it was demonstrated that oocyst‐sized microspheres are a useful tool during filtration‐optimization studies and performance assessments.
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Forest catchments can produce high quality source water with a low turbidity. However, the combination of low turbidity, low organic carbon, and low temperature water conditions presents operating challenges in conventional water... more
Forest catchments can produce high quality source water with a low turbidity. However, the combination of low turbidity, low organic carbon, and low temperature water conditions presents operating challenges in conventional water treatment processes. In this study, in-line filtration was tested using pilot-scale filter columns, and was found to be an appropriate option to treat a typical low turbidity water originating from the Rocky Mountains near Calgary, Alberta, Canada. When alum and cationic polymer were dosed simultaneously, in-line filtration produced high quality effluent with a turbidity and a particle count value of less than 0.1 NTU and 50 counts/mL, respectively. However, the alum and polymer doses and their ratios played important roles in the filtration efficiency. In general, short filter ripening times (i.e. &lt;15 min) required an alum dose of at least 3 mg/L and an alum to polymer dose ratio of less than 180:1. A longer filter stable period was associated with lower alum and polymer doses, as long as their doses were at least 2 and 0.024 mg/L, respectively, and their dose ratio was maintained in the range of 30:1 to 130:1. The optimal alum and polymer doses were observed to be 3 and 0.072 mg/L, respectively. Filter performance was enhanced when higher alum and polymer doses were used for ripening, and lower doses were applied during the stable filtration period. In addition, in-line filtration resulted in the reduction of microspheres by 3.6 logs under the tested water conditions. Hence, a similar removal efficiency is anticipated for Cryptosporidium.
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Physicochemical removal of protozoan pathogens is receiving increased attention because of the difficulty of chemically inactivating these organisms, particularly Cryptosporidium parvum. Most studies that have examined the removal of... more
Physicochemical removal of protozoan pathogens is receiving increased attention because of the difficulty of chemically inactivating these organisms, particularly Cryptosporidium parvum. Most studies that have examined the removal of these and other pathogens by filtration have been conducted under steady-state conditions with optimized pre-treatment. The research on which this paper is based evaluated the removal of Cryptosporidium and surrogates at various points in the filter cycle and under non-optimal conditions, at several pilot plants. The focus of this paper is on the relationship between removals of Cryptosporidium, and turbidity and particle counts. Under stable or optimal operating conditions all pilot plants produced similar low filter effluent turbidity and particle counts. Average Cryptosporidium removal varied among locations, however, by more than two log units. Cryptosporidium removal was impaired under all of the non-optimal conditions. Particle and turbidity performance was also worse, but the relationship of these parameters to Cryptosporidium removal varied. Particle counts show greater promise than turbidity as a tool to monitor filter performance in real time for possible deterioration in Cryptosporidium removal capability.
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Concentrations of particular types of microorganisms are commonly measured in various waters, yet the accuracy and precision of reported microorganism concentration values are often questioned due to the imperfect analytical recovery of... more
Concentrations of particular types of microorganisms are commonly measured in various waters, yet the accuracy and precision of reported microorganism concentration values are often questioned due to the imperfect analytical recovery of quantitative microbiological methods and the considerable variation among fully replicated measurements. The random error in analytical recovery estimates and unbiased concentration estimates may be attributable to several sources, and knowing the relative contribution from each source can facilitate strategic design of experiments to yield more precise data or provide an acceptable level of information with fewer data. Herein, variance decomposition using the law of total variance is applied to previously published probabilistic models to explore the relative contributions of various sources of random error and to develop tools to aid experimental design. This work focuses upon enumeration-based methods with imperfect analytical recovery (such as enumeration of Cryptosporidium oocysts), but the results also yield insights about plating methods and microbial methods in general. Using two hypothetical analytical recovery profiles, the variance decomposition method is used to explore 1) the design of an experiment to quantify variation in analytical recovery (including the size and precision of seeding suspensions and the number of samples), and 2) the design of an experiment to estimate a single microorganism concentration (including sample volume, effects of improving analytical recovery, and replication). In one illustrative example, a strategically designed analytical recovery experiment with 6 seeded samples would provide as much information as an alternative experiment with 15 seeded samples. Several examples of diminishing returns are illustrated to show that efforts to reduce error in analytical recovery and concentration estimates can have negligible effect if they are directed at trivial error sources.
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Wildfire can exert considerable influence on many watershed processes, including the partitioning of precipitation by forest canopies. Despite general acknowledgement that canopy interception is reduced following wildfire, effects on net... more
Wildfire can exert considerable influence on many watershed processes, including the partitioning of precipitation by forest canopies. Despite general acknowledgement that canopy interception is reduced following wildfire, effects on net rainfall and snow accumulation have not been quantified. The objectives of this study were to document net rainfall and snow water equivalent (SWE) in burned and unburned (reference) forest stands over a 10-year period to characterise the effects of severe wildfire on net precipitation in the Canadian Rocky Mountains. Differences in summer (June–September) rainfall between burned and reference stands suggest that wildfire reduced rainfall interception by 65%, resulting in a 48% increase in net rainfall from 2006 to 2008. This represented an average annual increase in net rainfall of 122mm (36%) for 10 years after the fire. Similarly, a burned stand had 152mm (78%) higher mean annual peak SWE than a paired reference stand. Collectively, burned stands had 274mm (191–344mm; 51%) more mean annual net precipitation for the first decade after fire. These results suggest that increases in net precipitation are likely following wildfire in subalpine forests and that, owing to the slow growth of these forests, post-fire changes may alter precipitation–runoff relationships for many years.
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Microbial contaminants are often regulated differently than chemical contaminants. Microorganisms are enumerated by techniques that are frequently susceptible to considerable losses, resulting in highly variable recoveries. Accordingly,... more
Microbial contaminants are often regulated differently than chemical contaminants. Microorganisms are enumerated by techniques that are frequently susceptible to considerable losses, resulting in highly variable recoveries. Accordingly, several treatment technique‐based regulations have evolved for microbial treatment. However, even these regulations ultimately require some reliance on microbial concentration data. Statistical approaches have been developed for the calculation of confidence intervals for microbial concentrations and removals by treatment processes, and these approaches take into account the various errors associated with microbial enumeration. The approaches were used here to demonstrate the relationship between methodological error and the practicality of concentration‐based regulations that require continuous and/or frequent monitoring, demonstrate the necessity of treatment technique‐based regulations such as the Long Term 2 Enhanced Surface Water Treatment Rule, demonstrate that methodological uncertainty is more substantially reduced by increasing organism count than by improving methodological recovery, and propose sampling targets of approximately 10 or more organisms to appreciably reduce the uncertainty associated with microbial quantification
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ABSTRACT Fluorescent microsphere has been used as pathogen surrogates in pathogen transport studies. A common technique, direct counting by epifluorescence microscopy, for the enumeration of virus- and bacteria-sized microsphere has been... more
ABSTRACT Fluorescent microsphere has been used as pathogen surrogates in pathogen transport studies. A common technique, direct counting by epifluorescence microscopy, for the enumeration of virus- and bacteria-sized microsphere has been applied in laboratory and field studies. However, few studies have focused on factors ensuring precise and accurate measures. Factorial experiment and two-way ANOVA with repeated measures performed to investigate the factors affecting the data quality. The evaluated factors were 1) the density of microspheres in each field and 2) the total number of counts in an enumeration. Two parameters, relative standard deviation and percent error, were used to assess methodological precision and accuracy. In addition, two water compositions with different ionic strength, i.e., calcite-saturated artificial groundwater (AGW) and deionized water (DIW) was used for assessing the effect of ionic strength and presence of precipitates. A standard method was used to prepare slides and enumerate microspheres, with particular care to randomly select fields for counting. As a result of visual observations of the slides, undulation in the filter membrane, bubble entrained in the mounting medium, and the presence of precipitates that form in AGW create biases in microsphere enumeration. As result of statistical assessment, microsphere density was found to be critical for ensuring methodological precision, whereas the total number of microspheres counted was essential to ensuring methodological accuracy. The results suggested that to minimize variability using the field approach, the enumeration of at least 350 microspheres and 25-40 microspheres field-1 is necessary.