This study investigates the potential for an aquifer to provide treatment of stormwater in addition to engineered treatment for the safe use of recovered water for drinking and non-drinking supplies. ...A brackish limestone aquifer was investigated as a treatment barrier when assessing microbial health-based targets of stormwater harvesting systems. Aquifer treatment was assessed based on pathogen inactivation and attachment to the aquifer sediments. The results showed that the health-based targets for different end uses including open space irrigation, domestic and industrial non-potable uses and drinking water could be met with additional treatment. The aquifer was estimated to have potential for ~4 log₁₀removal based on inactivation studies and attachment to the aquifer.
We investigated transport of viruses through saturated and unsaturated sand columns. Unsaturated experiments were conducted under conditions of uniform saturation and steady state water flow. The ...water saturation ranged from 1 to 0.5. Bacteriophages MS2 and ϕX174 were used as surrogates for pathogenic viruses in these studies. Phosphate‐buffered solutions with different pH values (7.5, 6.2, 5.5, and 5) were utilized. Virus transport was modeled assuming first‐order kinetic adsorption for interactions to the solid‐water interface (SWI) and the air‐water interface (AWI). Under saturated conditions, virus retention increased as pH decreased, and a one‐site kinetic model produced a good fit to the breakthrough curves. Under unsaturated conditions a two‐site kinetic model was needed to fit the breakthrough curves satisfactorily. The second site was attributed to the adsorption of phages to the AWI. According to our results, ϕX174 exhibits a high affinity to the AWI at pH values below 6.6 (the isoelectric point of ϕX174). Although it is believed that MS2 is more hydrophobic than ϕX174, MS2 had a lower affinity to the AWI than ϕX174, presumably because of the lower isoelectric point of MS2, which is equal to 3.9. Under unsaturated conditions, viruses captured within the column could be recovered in the column outflow by resaturating and immediately draining the column. Draining columns under saturated conditions, however, did not result in any recovery of viruses. Therefore the recovery can be attributed to the release of viruses adsorbed to the AWI. Our results suggest that electrostatic interactions of viruses with the AWI are much more important than hydrophobicity.
With the release of the Australian Guidelines for Water Recycling: Managed Aquifer Recharge (MAR), aquifers are now being considered as a treatment barrier when assessing the human health risk of ...recycled water systems. An MAR research site recharging urban stormwater in a confined aquifer was used in conjunction with a quantitative microbial risk assessment to assess the microbial pathogen risk in the recovered water for drinking. The assessment involved undertaking a detailed assessment of the treatment steps and exposure controls, including the aquifer, to achieve the microbial health-based targets.
The transport of viruses in unsaturated porous media has been a subject of great interest in recent years because of the enhanced removal of these microorganisms compared with saturated conditions. ...We studied the transport of bacteriophages MS2 and φX174, used as surrogate pathogenic viruses, at various water contents and solution chemistries in terms of pH and ionic strength (IS). The objective was to explore the interaction of viruses with the solid-water interfaces (SWI) and air-water interfaces (AWI) for a range of conditions. The experimental data were fitted with a transport model to determine the adsorption (attachment and detachment rate) parameters. Our results show that the retention of viruses in the soil column increases as water saturation decreases when the chemical conditions are favorable for adsorption (pH 7 and relatively high IS). Our analysis indicates that the enhanced retention of φX174 viruses at lower water contents is caused by increased attachment to the SWI and that retention by the AWI is not significant. Results obtained from a first series of experiments (pH 9 and low IS) showed insignificant attachment of MS2 viruses to both the SWI and the AWI. The MS2 breakthrough data for a second series of experiments (pH 7 and high IS) did not allow us to separate out the role of the AWI. Although attachment of MS2 viruses to the AWI cannot be ruled out in our experiments, we suspect that the increased retention of this phage under unsaturated condition was also due to enhanced attachment to the SWI. Increased attachment to the SWI under unsaturated conditions is attributed to increased mass transfer of viruses to the SWI due to a reduced diffusion length at lower water contents. Our results demonstrate that if there is any attachment to the AWI, it is reversible. When unfavorable conditions occur for attachment to the SWI, the attached viruses may be detached by moving solid-water-air contact lines (SWA).
Our ability to accurately simulate the transport and retention of colloids in the vadose zone is currently limited by our lack of basic understanding of colloid retention processes that occur at the ...pore scale. This review discusses our current knowledge of physical and chemical mechanisms, factors, and models of colloid transport and retention at the interface, collector, and pore scales. The interface scale is well suited for studying the interaction energy and hydrodynamic forces and torques that act on colloids near interfaces. Solid surface roughness is reported to have a significant influence on both adhesive and applied hydrodynamic forces and torques, whereas non-Derjaguin-Landau-Verwey-Overbeek (DLVO) forces such as hydrophobic and capillary forces are likely to play a significant role in colloid interactions with the air-water interface. The flow field can be solved and mass transfer processes can be quantified at the collector scale. Here the potential for colloid attachment in the presence of hydrodynamic forces is determined from a balance of applied and adhesive torques. The fraction of the collector surface that contributes to attachment has been demonstrated to depend on both physical and chemical conditions. Processes of colloid mass transfer and retention can also be calculated at the pore scale. Differences in collector- and pore-scale studies occur as a result of the presence of small pore spaces that are associated with multiple interfaces and zones of relative flow stagnation. Here a variety of straining processes may occur in saturated and unsaturated systems, as well as colloid size exclusion. Our current knowledge of straining processes is still incomplete, but recent research indicates a strong coupling of hydrodynamics, solution chemistry, and colloid concentration on these processes, as well as a dependency on the size of the colloid, the solid grain, and the water content.
Filtration theory does not include the potential influence of pore structure on colloid removal by straining. Conversely, previous research on straining has not considered the possible influence of ...chemical interactions. Experimental and theoretical studies were therefore undertaken to explore the coupling of physical and chemical mechanisms of colloid straining under unfavorable attachment conditions (pH=10). Negatively charged latex microspheres (1.1 and 3
μm) and quartz sands (360, 240, and 150
μm) were used in packed column studies that encompassed a range in suspension ionic strengths (6–106
mM) and Darcy water velocities (0.1–0.45
cm
min
−1). Derjaguin–Landau–Verwey–Overbeek (DLVO) calculations and torque analysis suggests that attachment of colloids to the solid–water interface was not a significant mechanism of deposition for the selected experimental conditions. Effluent concentration curves and hyperexponential deposition profiles were strongly dependent on the solution chemistry, the system hydrodynamics, and the colloid and collector grain size, with greater deposition occurring for increasing ionic strength, lower flow rates, and larger ratios of the colloid to the median grain diameter. Increasing the solution ionic strength is believed to increase the force and number of colloids in the secondary minimum of the DLVO interaction energy profile. These weakly associated colloids can be funneled to small regions of the pore space formed adjacent to grain–grain junctions. For select systems, the ionic strength of the eluant solution was decreased to 6
mM following the recovery of the effluent concentration curve. In this case, only a small portion of the deposited colloids was recovered in the effluent and the majority was still retained in the sand. These observations suggest that the extent of colloid removal by straining is strongly coupled to solution chemistry.
Packed column and mathematical modeling studies were conducted to explore the influence of water saturation, pore-water ionic strength, and grain size on the transport of latex microspheres (1.1 μm) ...in porous media. Experiments were carried out under chemically unfavorable conditions for colloid attachment to both solid–water interfaces (SWI) and air–water interfaces (AWI) using negatively charged and hydrophilic colloids and modifying the solution chemistry with a bicarbonate buffer to pH 10. Interaction energy calculations and complementary batch experiments were conducted and demonstrated that partitioning of colloids to the SWI and AWI was insignificant across the range of the ionic strengths considered. The breakthrough curve and final deposition profile were measured in each experiment indicating colloid retention was highly dependent on the suspension ionic strength, water content, and sand grain size. In contrast to conventional filtration theory, most colloids were found deposited close to the column inlet, and hyper-exponential deposition profiles were observed. A mathematical model, accounting for time- and depth-dependent straining, produced a reasonably good fit for both the breakthrough curves and final deposition profiles. Experimental and modeling results suggest that straining — the retention of colloids in low velocity regions of porous media such as grain junctions — was the primary mechanism of colloid retention under both saturated and unsaturated conditions. The extent of stagnant regions of flow within the pore structure is enhanced with decreasing water content, leading to a greater amount of retention. Ionic strength also contributes to straining, because the number of colloids that are held in the secondary energy minimum increases with ionic strength. These weakly associated colloids are prone to be translated to stagnation regions formed at grain–grain junctions, the solid–water–air triple point, and dead-end pores and then becoming trapped.
Aquifer Storage and Recovery (ASR) has been used for decades as a technique to store harvested urban stormwater in aquifers for subsequent reuse. However, stormwater recycling via ASR may also ...provide a means of improving the quality of the recharged water through passage and storage in the aquifer, thereby allowing improved prediction and management of recovered water quality. In this study, water quality data were evaluated from four stormwater ASR sites operating for up to 14 years in Salisbury, South Australia. Stormwater was injected and stored in a confined carbonate aquifer that initially contained brackish water. Long term operational monitoring of stormwater recycling via ASR was used to quantify the changes in salinity, turbidity and Escherichia coli concentrations. At all sites, E. coli concentrations in recovered water was 2–3log10 (90 to 99%) less than injected water. Positive detections of E. coli were found >98% injected water samples in comparison with ∼20% of recovered water samples from all four sites. Turbidity reduction was >50% for three of the ASR sites. Reductions could not be explained through dilution alone and are the result of bacteria retention and inactivation in the aquifer. The magnitude of E. coli removal, and to a lesser degree turbidity reduction, highlights the potential for integration with engineered treatments.
1 We investigated transport of viruses through saturated and unsaturated sand columns. Unsaturated experiments were conducted under conditions of uniform saturation and steady state water flow. The ...water saturation ranged from 1 to 0.5. Bacteriophages MS2 and phiX174 were used as surrogates for pathogenic viruses in these studies. Phosphate-buffered solutions with different pH values (7.5, 6.2, 5.5, and 5) were utilized. Virus transport was modeled assuming first-order kinetic adsorption for interactions to the solid-water interface (SWI) and the air-water interface (AWI). Under saturated conditions, virus retention increased as pH decreased, and a one-site kinetic model produced a good fit to the breakthrough curves. Under unsaturated conditions a two-site kinetic model was needed to fit the breakthrough curves satisfactorily. The second site was attributed to the adsorption of phages to the AWI. According to our results, phiX174 exhibits a high affinity to the AWI at pH values below 6.6 (the isoelectric point of phiX174). Although it is believed that MS2 is more hydrophobic than phiX174, MS2 had a lower affinity to the AWI than phiX174, presumably because of the lower isoelectric point of MS2, which is equal to 3.9. Under unsaturated conditions, viruses captured within the column could be recovered in the column outflow by resaturating and immediately draining the column. Draining columns under saturated conditions, however, did not result in any recovery of viruses. Therefore the recovery can be attributed to the release of viruses adsorbed to the AWI. Our results suggest that electrostatic interactions of viruses with the AWI are much more important than hydrophobicity.
Coronary artery disease (CAD) is among the main causes of death in adults. Increase of oxidative stress and defects in antioxidant defense play a major role in endothelium performance and are ...affecting factors in the progress of atherosclerosis. The aim of this study was to measure serum levels of uric acid (UA) and vitamin C as well as the antioxidant status in patients with CAD, and compared them with those in healthy individuals. The present case-control study was performed on 44 cases and 44 controls. Demographic data and anthropometric indices were measured. The Food Frequency Questionnaire (FFQ) and International Physical Activity Questionnaire (IPAQ) were completed. After 12 hours of fasting,10 mL blood was sampled from the participants. Serum levels of UA, vitamin C, Total Antioxidant Capacity (TAC) and Malondialdehyde (MDA) were also measured. The data were finally analyzed by SPSS v22. A significant difference was observed between the groups in terms of UA and vitamin C. However, mean levels of MDA and TAC were not significantly different between groups. The differences between groups in terms of vitamin A, vitamin E, beta-carotene, zinc and selenium intakes were not significant either. A significant difference was detected between the groups in terms of vitamin C intake. Our results suggest that increase in UA and decrease in vitamin C in serum levels can be considered as risk factors for CAD patients. Due to a lack of any significant correlation between TAC and CAD risk in this study, further study with bigger sample size is needed.
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