Abstract
Micro-nano bubbles (MNBs) technology has shown great potential in groundwater bioremediation because of their large specific surface area, negatively charged surface, long stagnation, high oxygen transfer efficiency, etc. Groundwater salinity, which varies from sites due to different geological and environmental conditions, has a strong impact on the bioremediation effect. However, the groundwater salinity effect on MNBs’ behavior has not been reported. In this study, the size distribution, oxygen transfer efficiency and zeta potential of MNBs was investigated in different salt concentrations. In addition, the permeability of MNBs’ water through sand in different salt concentrations was studied. The results showed that water salinity has no influence on bubble size distribution during MNBs generation. MNBs could greatly enhance the oxygen transfer efficiency from inner bubbles to outer water, which may greatly enhance aerobic bioremediation. However, the enhancement varied depending on salt concentration. 0.7 g/L was found to be the optimal salt concentration to transfer oxygen. Moreover, MNBs in water salinity of 0.7 g/L had the minimum zeta potential. The correlation of zeta potential and mass transfer was discussed. The hydraulic conductivities of sand were similar for MNBs water with different salt concentrations. The results suggested that salinity had a great influence on MNBs performance, and groundwater salinity should be taken into careful consideration in applying MNBs technology to the enhancement of bioremediation.
Highlights
In situ groundwater bioremediation is one of the most common and environment-friendly methods to remediate polluted groundwater [1,2,3,4,5]
The water salinity had no impact on the Micro-nano bubbles (MNBs) water permeability of sand
Water salinity had no influence on MNBs size
Summary
In situ groundwater bioremediation is one of the most common and environment-friendly methods to remediate polluted groundwater [1,2,3,4,5]. The activity of microorganisms is related to dissolved oxygen availability, groundwater salinity, nutrients, pH value, etc. Sea water invasion in offshore area and human activities will influence the groundwater salinity [12]. Micro-nano bubbles (MNBs) technology has attracted much interest in bio-related areas such as bioremediation, aquaculture and plant cultivation [18,19,20]. Micro bubbles with a 30 μm radius were first found by Turner [21] in water and existed for long time, probably because the surface properties were changed to support the excess inner gas pressure which would slow down the gas diffusion process
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