## 5 Results and Discussion
### Wastewater Treatment
#### 5.2.2 Centella asiatica  
Figure 3 also shows readings for the Al content accumulated by _C. asiatica_ for 10 days of treatment. Readings recorded on day 0, 2, 4, 6, 8, and 10 were \(\sim\)0.30, 0.20, 0.13, 0.0, 0.10, and 0.05 mg/L, respectively.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Industrial Wastewater** & \
\begin{tabular}{c} **Department of Environment (DOE) (2009)** \\ **Standard A** \\ \end{tabular} &
\begin{tabular}{c} **Standard B** \\ \end{tabular} \\ \hline pH & 7.86 & 6.0–9.0 & 5.5–9.0 \\ Temperature (°C) & 31.0 & 40 & 40 \\ Turbidity (NTU) & 20.07 & - & - \\ Total Dissolved Solid (mg/L) & 1132 & - & - \\ Conductivity (\(\mathrm{\SIUnitSymbolMicro s}\)) & 1613 & - & - \\ Fluoride (\(\mathrm{\SIUnitSymbolFace}\)) & 0.8 & 2.0 & 5.0 \\ Nitrate (mg/L) & 41.52 & - & - \\ Chemical Oxygen Demand (mg/L) & 40 & - & - \\ Biological Oxygen Demand (mg/L) & 5.6 & - & - \\ Hardness (mg/L) & 829 & - & - \\ \hline \multirow{2}{*}{**Element**} & \multicolumn{2}{c}{**Heavy Metals**} & \multirow{2}{*}{**Department of Environment (DOE) (2009) (mg/L)**} \\  & **Concentration (mg/L)** & & & \\ \hline Aluminum & 0.30 & 10 & 15 \\ Barium & 0.12 & 1.0 & 2.0 \\ Calcium & 136.84 & - & - \\ Iron & 1.09 & 1.0 & 5.0 \\ Potassium & 12.58 & - & - \\ Lithium & 0.02 & - & - \\ Magnesium & 11.02 & - & - \\ Manganese & 0.07 & 0.20 & 1.0 \\ Nickel & 0.01 & 0.20 & 1.0 \\ Rubidium & 0.03 & - & - \\ Strontium & 0.35 & - & - \\ Zinc & 0.07 & 2.0 & 2.0 \\ \hline \hline \end{tabular}  
* not detected, elements: Arsenic, Beryllium, Bismuth, Cadmium, Cobalt, Chromium, Caesium, Copper, Gallium, Lead, Selenium, silver.  
\end{table}
Table 1: Analysis of the heavy metal content from industrial wastewater.  
Figure 3: Reduction of: (**a**) Al concentration by _Ipomnea aquatic_; (**b**) Al concentration by _Centella asiatica_; (**c**) Fe concentration by _Ipomnea aquatic_; and (**d**) Fe concentration by _Centella asiatica_.  
On the final day of treatment, the heavy-metal concentration decreased by 83%. A significant drop was recorded on the second day of treatment, which was \(\sim\)33%. Figure 3 also shows readings for the Fe content for 10 days of treatment. Readings recorded on day 0, 2, 4, 6, 8, and 10 were \(\sim\)1.09, 0.90, 0.83, 0.78, 0.79, and 0.60 mg/L, respectively. The heavy-metal concentration decreased by 45% on the final day of treatment. A significant drop was recorded on the second day of treatment, which was \(\sim\)17%.  
The present study found evidence of the ability of _C. asiatica_ and _I. aquatica_ as phytoremediation plants for removing Al and Fe. These results were in good agreement with those reported previously, indicative of the ability of _C. asiatica_ and _I. aquatica_ for removing various pollutants. _C. asiatica_ and _I. aquatica_ were assessed in previous studies for its ability to remove various pollutants and water quality parameters, e.g., chemical oxygen demand (COD), biochemical oxygen demand (BOD), and ammoniacal nitrogen (NH\({}_{3}\)-N) [34], cadmium [35], lead [36], nitrate [37], total suspended solid (TSS) [38; 39], copper [40], phosphate [41; 42], nitrogen and phosphorus [43], and chromium (VI) [44]. Based on the previous studies, _C. asiatica_ was found to be more efficient to remove most of the pollutants compared to _I. aquatica_. By comparing the efficiency rate of _C. asiatica_ and _I. aquatica_ obtained from the present study, a similar pattern of results was found in [PERSON] et al. [3] that have identified _S. grossus_ as a hyperaccumulator in the phytoremediation of Al and Fe. It should be noted that, however, the removal percentage rate of pollutants varies depending on the type of wastewater, duration of treatment, concentration of pollutant, etc.