Micro-nano Bubbles Characteristics For Potential Application In Groundwater Remediation

Groundwater pollution by organic contaminants is becoming more and moresevere, making groundwater remediation imperative. Research on the remediationtechnology is of theoretical and practical importance.Based on the review of in-situ groundwater remediation technology for organiccontaminants, this study first evaluated the effectiveness of air sparging. Then,micro-nano bubbles (MNBs) technology was proposed for groundwater remediation.The MNBs’ physical properties, transport behavior in porous media and groundwaterremediation process were investigated systematically by experimental investigation,theoretical study and numerical simulation.In the study of air sparging, the centrifuge tests of air sparging were carried out toinvestigate the zone of influence, air flow pattern, etc. Based on the experimental results,the3D numerical model coupling two-phase (air-water) flow and contaminantstransport processes was established. The numerical simulation showed the contaminantswere removed mainly by inter-phase exchange within the zone of influence.Biodegradation was limited due to the poor supply of dissolved oxygen in groundwater.However, the dissolved oxygen in groundwater can be greatly enhanced by MNBs,which have high mass transfer efficiency and long stagnation time. In the study ofMNBs, the meso-scale observation system was designed, including camera, microscope,laser device, adjustable holder and postprocessing software. The observation system,together with size distribution analyzer and zeta potential analyzer was applied forresearch on MNBs’ properties. The MNBs size distribution and zeta potential wereobtained. High gas mass transfer efficiency and long stagnation time of MNBs in waterwere verified by test data. The transport behavior in water and porous media wasunderstood as well.The theoretical model of MNBs transport in porous media was proposed. MNBstransported in porous media as colloid, with neglectable diffusion effect. The advection,dispersion, adsorption and dissolution of MNBs should be considered in the proposedmodel. The numerical model was developed, coupling MNBs transport, groundwaterflow and dissolved oxygen transport, to simulate the MNBs water flow in porous media.The result of numercal model was reasonable, verified by laboratory test data.The scheme using MNBs for in-situ groundwater remediation was presented. Thecontaminants can be removed by biodegradation enhanced by MNBs. The numerical simulation results of in-situ application showed a great enhancement on dissolvedoxygen and a significant influence zone for contaminant removal.MNBs technology was effective, energy-efficient and environment-friendly toclean up contaminants, which has great potential in groundwater remediation.