# Remediation of Copper Contaminated Soils Using Water Containing Hydrogen Nanobubbles
## 3 Results
### Electrokinetic Test  
An electrokinetic remediation test was carried out, with the nanobubbles acting as an enhancer for copper-contaminated soil. The current density and effluent changes, according to the soil type, were then determined. The copper and pH in soil after completion of the experiment were also determined.  
Figure 7 illustrates changes in the current density according to different types of soil. Clay (DW) corresponds to a peak current density of 9.21 (mA/cm\({}^{2}\)) at 5 h from the start of the experiment. Clay (NBW) corresponds to a peak current density of 9.81 (mA/cm\({}^{2}\)) at 8 h from the start of the experiment. Sand (DW) corresponds to a peak current density of 0.88 (mA/cm\({}^{2}\)) at 24 h from the start of the experiment, and Sand (NBW) corresponds to a peak current density of 0.74 (mA/cm\({}^{2}\)) at 5 h from the start of the experiment. Both sand and clay exhibited an initial increase, followed by a decrease in the current density. The result of all the tests tended to converge as time went by. The migration of heavy metal ions increased initially and then decreased. [PERSON] et al. [19] postulate that this might be attributable to the migration and sedimentation of the heavy metal ions.  
Figure 8 illustrates the amount of effluent according to the remediation time for sand and clay as part of the remediation experiment, where nanobubbles were used as an enhancer. Effluents of Clay (DW), Clay (NBW), Sand (DW), and Sand (NBW) were 729, 662, 5855, and 1198 mL, respectively. The amount of effluent from the one treated with distilled water was found to be greater than the outflow observed with the nanobubbles treatment. This was attributed to bubbles of hydrogen gas being generated at the cathode by electrokinetic remediation with nanobubbles that disturbed the discharge of the effluent. The amount of effluent from sand appeared greater than that outflowing from clay. The removal of heavy metal from sand with greater effluent discharge was found to be highly efficient. This could be attributed to the comparatively larger specific surface area and zeta-potential of the nanobubbles that resulted in remediation being more efficient.  
Figure 9 illustrates the concentrations of residual heavy metals and pH level measured at each position in the cell upon completion of the experiment. In the case of sand and clay, all exhibited an increased pH due to the collision of acid and base at the point of 0.75 x/L by electrokinetic remediation.  
Remediation of copper contamination occurred, as compared to the initial state of the specimen. The migration and accumulation of heavy metal by electrokinetic remediation were identified at a point of 0.75 (x/L) [20]. The efficiency of the removal of heavy metals from the specimens contaminated by heavy metal increased by the contact of the nanobubbles and by the high ratio of the void in sand, which increased the flow of effluent through the copper-contaminated soil under basic conditions [21; 22].  
Figure 7: Current density.  
The nanobubbles were made of hydrogen gas in distilled water and have an initial neutral pH 7. In the case of sand, the initial pH was influenced by the initial pH due to the inflow of nanobubbles in water, and it can be seen that the pH change at the point of 0.1 to 0.7 (x/L) is small. Sand has a smaller void than clay, and heavy metals adhere to the surface, so the sand is considered to be desorbed when passing through the void of the nanobubbles.