Study On Natural Colloid Characteristic And Itstransportation Under Managed Aquifer Recharge Condition

Managed aquifer recharge can reduce a lot of environment geological problems such as ground subsidence, cracks and also on. At the same time, the injection of recharge water will damage the balance of dynamic condition and chemical condition of original groundwater. Then it will influence the groundwater quality of recharge area. As colloid exists widely in groundwater, and it can affect the transport of heavy metal and inorganic constituents in groundwater.In order to clarify the kind and transport regularity of natrure colloid in groundwater, field investigations, laboratory experiments, numerical simulations were used in this study. Main results of this paper are as follows:1. Field recharge water and original groundwater were ultrafiltrated for analysis. According to the test results of water quality and each filtration membrane, the kind of natrure colloid were identified. Results shows: inorganic colloid accounted for the main part in the particle size range of 50~100KDa and organic colloids accounted for the main part of in 50 KDa. According to the site conditions, considering all components in the proportion of organic and inorganic colloid, humic acid(HA) was selected to represent organic colloid and silica was selected to represent inorganic colloid in this study.2. On the basis of colloid species identification, size and zeta potential of HA and silica under different chemical condition and dynamic condition were examined. Including size and zeta potential of HA and silica colloid change with pH and IS. Which humic acid and silica colloidal particle diameter and zeta potential were with the increase of suspension p H, and with the increase of IS, its size increases and potential(negative potential) showed a downward trend.3. Monitored the transport of HA throughout the migration process by colloid realtime monitoring platform. Studied migration mechanism of natural colloid in aquifer under different IS(<0.0005 M, 0.02 M, 0.05M), different pH(5, 7, 9) and different flow rate(0.1ml/min,0.2ml/min, 0.4ml/min) by monitoring variations of concentration and size of HA and silica colloid with DLVO interaction energy correlation. Results show that the migration process in porous media of HA and silica colloid are different under different conditions. It indicates that except IS and pH, the kind of colloid has influence on the transport process. IS has the most significantly effect on its migration process and flow rate and pH also affect its migration in aquifer.4. On the basis of field investigation and laboratory experimental results, COMSOL Multiphysics were used to simulate the migration process of HA and silica colloid in porous media. It was found that with the increase of IS, the Attachment rate attk increased obviously, that is to say the effect of IS on the deposition process was obvious. The simulation results show that the leaching of early 1PV, there are two colloid release phenomenon, along with the continuous leaching, The colloid concentration is lower than the detection limit, which indicates that the colloid migration ability is strong, and there is a threat to the water quality in the irrigation area.