Modeling Virus Transport and Removal during Storage and Recovery in Heterogeneous Aquifers (original) (raw)
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Modeling Virus Transport and Removal during Aquifer Storage and Recovery
Journal of Hydrology, 2019
A quantitative understanding of virus removal during aquifer storage and recovery (ASR) in physically and geochemically heterogeneous aquifers is needed to accurately assess human health risks from viral infections. A two-dimensional axisymmetric numerical model incorporating processes of virus attachment, detachment, and inactivation in aqueous and solid phases was developed to systematically evaluate the virus removal performance of ASR schemes. Physical heterogeneity was considered as either layered or randomly distributed hydraulic conductivities (with selected variance and horizontal correlation length). Geochemical heterogeneity in the aquifer was accounted for using Colloid Filtration Theory to predict the spatial distribution of attachment rate coefficient. Simulation results demonstrate that the combined effects of aquifer physical heterogeneity and spatial variability of attachment rate resulted in higher virus concentrations in the recovered water at the ASR well (i.e. reduced virus removal). While the sticking efficiency of viruses to aquifer sediments was found to significantly influence virus concentration in the recovered water, the solid phase inactivation under realistic field conditions combined with the duration of storage phase had a predominant influence on the overall virus removal. The relative importance of physical heterogeneity increased under physicochemical conditions that reduced virus removal (e.g. lower value of sticking efficiency or solid phase inactivation rate). This study provides valuable insight on site selection of ASR projects and an approach to optimize ASR operational parameters (e.g. storage time) for virus removal and to minimize costs associated with post-recovery treatment. Several studies have reported that viruses can travel several hundred meters or may be viable for several months (or even years) under certain environmental conditions (Sidhu et al., 2015; Torkzaban et al., 2006; Schijven et al., 2016). The potential for large transport distance and long-term survival for pathogenic viruses in aquifers is a significant public health concern. Indeed, one of the main impediments to the uptake of ASR has been attributed to the presence of pathogenic viruses in the recovered water (NRMMC-EPHC-NHMRC, 2009). Recovered ASR water is therefore subjected to expensive post-treatments to remove/ inactivate pathogens (Dillon et al., 2010). Schijven and Hassanizadeh (2000) presented a comprehensive review on factors and processes influencing virus removal in laboratory and field studies. Processes influencing virus transport and removal in aquifers include advective and dispersive transport, attachment to and detachment from sediment surfaces, and inactivation in aqueous and on
Transport and fate of viruses in sediment and stormwater from a Managed Aquifer Recharge site
Journal of Hydrology, 2017
Enteric viruses are one of the major concerns in water reclamation and reuse at Managed Aquifer Recharge (MAR) sites. In this study, the transport and fate of bacteriophages MS2, PRD1, and ΦX174 were studied in sediment and stormwater (SW) collected from a MAR site in Parafield, Australia. Column experiments were conducted using SW, stormwater in equilibrium with the aquifer sediment (EQ-SW), and two pore-water velocities (1 and 5 m day-1) to encompass expected behavior at the MAR site. The aquifer sediment removed >92.3% of these viruses under all of the considered MAR conditions. However, much greater virus removal (4.6 logs) occurred at the lower pore-water velocity and in EQ-SW that had a higher ionic strength and Ca 2+ concentration. Virus removal was greatest for MS2, followed by PRD1, and then ΦX174 for a given physicochemical condition. The vast majority of the attached viruses were irreversibly attached or inactivated on the solid phase, and injection of Milli-Q water or beef extract at pH=10 only mobilized a small fraction of attached viruses (<0.64%). Virus breakthrough curves (BTCs) were successfully simulated using an advective-dispersive model that accounted for rates of attachment (k att), detachment (k det), irreversible attachment or solid phase inactivation (μ s), and blocking. Existing MAR guidelines only consider the removal of viruses via liquid phase inactivation (μ l). However, our results indicated that k att > μ s > k det > μ l , and k att was several orders of magnitude greater than μ l. Therefore, current microbial risk assessment methods in the MAR guideline may be overly conservative in some instances. Interestingly, virus BTCs exhibited blocking behavior and the calculated solid surface area that contributed to the attachment was very small. Additional research is therefore warranted to study the potential influence of blocking on virus transport and potential implications for MAR guidelines.
Are Viruses a Hazard in Waste Water Recharge of Urban Sandstone Aquifers?
2007
Urban waste waters will often contain viruses, including human (and, topically, avian) viruses. Use of waste water in artificial recharge therefore requires a risk assessment of virus hazard, and establishing the knowledge needed for this in an example sandstone aquifer is the aim of the present SWITCH project (WP3.2). Presently there is some limited evidence that, even in predominantly matrix flow aquifers such as the Birmingham sandstone aquifer, viable human viruses can be transported to depths of at least 40 m. Horizontal transport distances are (even) less certain, but laboratory studies suggest survival times of < 2 years. To gain the knowledge necessary to develop rules for operation of AR schemes, a four-stranded approach is proposed: (i) field experimentation on a borehole array using bacteriophage as surrogates for human viruses; (ii) laboratory experimentation on intact cores; (iii) monitoring of virus concentrations at multi-level piezometers and pumping wells; and (iv) modelling. Work to date has concentrated on establishing the basic design of the field experiments, and has included hydraulic testing and checking for virus presence in the groundwaters of the test site.
Virus Transport Experiments in a Sandy Aquifer
Water, Air, and Soil Pollution, 2006
The occurrence of human enteric viruses in ground water has been well documented in the literature. Bacteriophages such as MS-2 and PRD1 have properties similar to pathogenic human viruses suggesting that bacteriophages can be used as proxies for virus transport. The objective of this study is to investigate a "worst case scenario" for virus transport in a ground water aquifer, i.e., sand and gravel aquifer under a forced-gradient, by using bacteriophages.
Advances in Water Resources, 2003
The likelihood for viruses, protozoan oocysts, and other human pathogens to enter groundwater, and in particular, sensitive or vulnerable water supplies, has increased as the numbers of anthropogenic sources such as septic systems, leaking sewers, animal farming operations, and artificial recharge of treated wastewater have proliferated. In this paper, we utilize a detailed numerical model of groundwater flow in a region encompassing a large artificial groundwater recharge operation in Orange County, California to evaluate the potential for transport of viruses and protozoan oocysts in such a system, as dictated by a transport model that includes colloid filtration and microbial inactivation components. The purpose of the model is not oriented towards the analysis of any perceived or real microbial contamination, but rather is directed at understanding the influence of aquifer heterogeneity within the modeled system. The transport model is based upon a novel representation of geologic heterogeneity, a high-resolution flow simulator, and an efficient streamline-based transport algorithm. Example virus transport simulations illustrate a large degree of variability in virus breakthrough across water supply pumping wells, with shallower wells providing less than two orders of magnitude of virus removal, and deeper wells indicating many orders of magnitude of virus removal. Simulation results also show variability among pathogens modeled, with Cryptosporidium parvum filtered to a much greater degree than other pathogens. Comparison to transport of an abiotic colloid and a conservative chemical tracer are provided to illustrate the influence of filtration and inactivation on the transport process. The results emphasize the need for improved microbial transport models in realistic aquifer systems, more reliable virus characterization methods and monitoring networks, and their ultimate integration into a broader epidemiological and regulatory framework for aquifer management.
Stochastic analysis of virus transport in aquifers
Water Resources Research, 1999
A large-scale model of virus transport in aquifers is derived using spectral perturbation analysis. The effects of spatial variability in aquifer hydraulic conductivity and virus transport (attachment, detachment, and inactivation) parameters on large-scale virus transport are evaluated. A stochastic mean model of virus transport is developed by linking a simple system of local-scale free-virus transport and attached-virus conservation equations from the current literature with a random-field representation of aquifer and virus transport properties. The resultant mean equations for free and attached viruses are found to differ considerably from the local-scale equations on which they are based and include effects such as a free-virus effective velocity that is a function of aquifer heterogeneity as well as virus transport parameters. Stochastic mean free-virus breakthrough curves are compared with local model output in order to observe the effects of spatial variability on mean one-dimensional virus transport in three-dimensionally heterogeneous porous media. Significant findings from this theoretical analysis include the following: (1) Stochastic model breakthrough occurs earlier than local model breakthrough, and this effect is most pronounced for the least conductive aquifers studied. (2) A high degree of aquifer heterogeneity can lead to virus breakthrough actually preceding that of a conservative tracer. (3) As the mean hydraulic conductivity is increased, the mean model shows less sensitivity to the variance of the natural-logarithm hydraulic conductivity and mean virus diameter. (4) Incorporation of a heterogeneous colloid filtration term results in higher predicted concentrations than a simple first-order adsorption term for a given mean attachment rate. (5) Incorporation of aquifer heterogeneity leads to a greater range of virus diameters for which significant breakthrough occurs. (6) The mean model is more sensitive to the inactivation rate of viruses associated with solid surfaces than to the inactivation rate of viruses in solution.
Water Research, 2020
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Virus Survival and Transport in Ground Water
Water Science and Technology, 1988
Viruses are a significant cause of waterborne disease in the United States; it has been estimated that they may be responsible for as much as 50% of the reported outbreaks. This fact has led the U.S. Environmental Protection Agency to propose a maximum contaminant level goal (MCLG) for viruses in drinking water. Septic tanks, which contribute over one trillion gallons of waste to the subsurface every year, are a major source of viruses in soils and ground water. The purpose of this research was to develop a model which could be used to estimate safe distances between septic tanks, or other sources of contamination, and drinking-water wells. The model was based on ground-water flow characteristics and the length of time that viruses remain infective in the subsurface environment. Water samples were collected from 71 continuously pumping municipal drinking-water wells. Viruses were inoculated into the water samples, and the rate at which the viruses were inactivated was calculated for...
Environmental Science & Technology, 2011
We propose an analytical solution in order to explain the processes that determine the fate and behavior of the viruses during transport in a fractured aquifer at Salento (Italy). The calculations yield the efficiency of filtration in fractures at a site near Nardò (Southern Italy) in reducing the numbers of enteric viruses (i.e., Enteroviruses and Norovirus) in secondary municipal effluents that have been injected in the aquifer over the period 2006-2007. The model predicted, by a theoretical expression, the time-dependent rate of virus reduction, which was in good agreement with field data. The analytical solution yields the achievable "Log reduction credits" (1) for virus reduction in wells located at the setback distances that are usually adopted in local drinking water regulations. The resulting new analytical formula for the time-dependent reduction of viruses during subsurface transport can easily be applied in health risk-based models used to forecast the spread of waterborne diseases and provides appropriate criteria (i.e., distances) needed to meet standards for the quality of drinking water derived from undisinfected groundwater.