# Remediation of Copper Contaminated Soils Using Water Containing Hydrogen Nanobubbles
## 3 Results  
### Batch Test  
Batch testing was carried out by varying the solid-liquid ratio and the contact time for different conditions of copper-contaminated soils, so as to allow samples to be purified, using nanobubbles as an enhancer. The results obtained from the batch test are as shown below.  
Figure 5 shows the incremental desorption percentage of copper according to changes in the solid-liquid ratios of soils contaminated with copper. After agitation for 24 h, the level of desorption of the heavy metal by the nanobubbles was found to be greater in sand than in clay. The increase in solid-liquid ratios in both sand and clay also increased the efficiency with which heavy metals were removed than compared to the use of distilled water alone. However, contrary to the proportional increase of the removal efficiency of the copper to solid-liquid ratio in sand, a solid-liquid ratio greater  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Parameters** & **Units** & **Conditions** \\ \hline \multirow{3}{*}{Fixed Factor} & Concentration (C\({}_{0}\)) & ppm & 500 (Copper) \\  & Electrokinetic & V/cm & 1 \\  & Gradient & & \\  & Contaminated Soil & x/L & 0.75 \\  & Bed & & \\  & Soil & - & Sand, Clay \\  & Enhancer & - & Distilled Water (DW) \\  & & & H\({}_{2}\)-Nanobubble Water (NBW) \\ Variable Factor & & & 10 (Clay) & Case 1 (DW) \\  & Duration Time & Day & 10 (Clay) & Case 2 (NBW) \\  & & & 5 (Sand) & Case 3 (DW) \\  & & & & Case 4 (NBW) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Electrokinetic test conditions.  
Figure 4: (a) Side view. (b) Floor plan. Diagram of the Electrokinetic system.  
than 1:20 in clay rendered no significant difference in the efficiency of the copper removal by DW and NBW. Taking both efficiency and economy into account, the optimal solid-liquid ratio, while using nanobubbles as an enhancer in sand, was determined to be 1:20. This finding was attributed to the comparatively larger specific surface area and zeta-potential of the nanobubbles, which is known to be advantageous for desorption and transfer of copper from the surface of particles [15; 18].  
The results of the batch test, according to variations in the reaction time with a constant solid-liquid ratio of 1:20, are presented in Figure 6. The nanobubbles demonstrated a greater efficiency for removing copper than distilled water. The efficiency of the copper removal varied according to the reaction time. Both distilled water and the nanobubbles initially increased desorption of copper. In the case of sand with 6 h of contact time, the highest removal efficiency of copper, by both distilled water and the nanobubbles, was 15.61% and 18.48% respectively. Thereafter, the removal efficiency of both distilled water and the nanobubbles tended to converge. In the case of clay, the highest removal efficiency (desorption of copper) of both distilled water and the nanobubbles was observed within the initial first hour. The appropriate interval for contact time by the nanobubbles was found to be 6 h for sand and 1 h for clay. The explanation for this variation could be that the characteristics of re-adsorption of copper from the surface of clay are greatly influenced by the clay's surface charge.  
Figure 5: Solid-liquid ration test.  
Figure 6: Contact time test (S:L = 1:20).