Abstract
Colloids may have an important role in regulating the structure and function of groundwater ecosystems, and may influence the migration of low solubility contaminants in groundwater. There is, however, a degree of uncertainty about how colloids behave under the variable hydrogeochemical and hydrodynamic conditions that occur during managed aquifer recharge. We used an online monitoring system to monitor the transport of silica colloid in saturated porous media under different hydrogeochemical conditions, including a range of pH values (5, 7, and 9), ionic strengths (<0.0005, 0.02, and 0.05 M), cation valences (Na+, Ca2+), flow rates (0.1, 0.2, and 0.4 mL/min). The results showed that silica colloid was more likely to deposit on the surface of porous media in acidic conditions (pH = 5) than in alkaline conditions (pH = 9), indicating that the risks of pollution from colloidal interactions would be higher when the pH of the recharge water was higher. Colloid deposition occurred when the ionic strength of the colloidal suspension increased, and bivalent cations had a greater effect than monovalent cations. This suggests that bivalent cation-rich recharge water might affect the porosity of the porous medium because of colloid deposition during the managed aquifer recharge process. As the flow rate increased, the migration ability of silica colloid increased. We simulated the migration of silica colloid in porous media with the COMSOL Multiphysics model.
Highlights
In recent years, managed aquifer recharge (MAR) has been used to mitigate a wide range of geological problems in the environment, such as ground subsidence, surface cracks, seawater intrusion, and groundwater depressions
By simulating different water chemical and hydrodynamic conditions, we tested the migration of inorganic colloids, represented by silica colloid in this study, in an aquifer that was receiving
The four groups of experimental results showed that, under variable water chemistry and hydrodynamic conditions, the migration of silica colloid in porous media was governed by different rules
Summary
In recent years, managed aquifer recharge (MAR) has been used to mitigate a wide range of geological problems in the environment, such as ground subsidence, surface cracks, seawater intrusion, and groundwater depressions. While MAR has some clear benefits, the injection of recharge water will negatively impact the equilibrium and chemical conditions of the original groundwater, which may have further consequences for the quality of the groundwater in the recharged aquifer [1]. Colloids are distributed widely in groundwater, and can affect the transport of heavy metal and inorganic constituents in groundwater [2,3]. It can affect a variety of other contaminants such as organic matter, bacteria, viruses, engineered nanoparticles, etc. To date, we still have not been able to determine the influence of changes in the groundwater dynamic and chemical conditions during MAR on colloid migration.
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