## 3 Results and Discussion
### Removal of TSS, NH\({}_{3}\)-N and COD
#### 3.2.3 Reduction Rate of COD
It can be seen in this study which the average reading of NH\({}_{3}\)-N was decreasing during the phytoremediation treatment. _Ipomoea aquatica_ reduced approximately 97.3% of NH\({}_{3}\)-N in the sewage wastewater sample. This plant was useful for removing nitrates from polluted water. By means of COD content, _Ipomoea aquatica_ has absorbed about 44.8% of COD in the sewage  
Figure 6. Percentage of reduction in TSS, NH\({}_{3}\)-N and COD for _Lenna minor_, _Salvinia minima_, _Ipomoea aquatica_ and _Centrella asiatica_. wasetwwater sample. The long and fibrous roots of _Ipomoea aquatic_ make it able to absorb nutrients in wastewater efficiently. This species is a fast-growing plant and needs pollutants as food to grow [46]. The statistical analysis using a one-way ANOVA test showed a significant difference (\(p<0.05\)) for the rate of reduction in the TSS, NH\({}_{3}\)-N and COD contents during the 8 days of phytoremediation treatment of sewage wastewater. With regards to _Centella asiatica_, the reduction percentage of TSS, NH\({}_{3}\)-N and COD in the sewage wastewater sample was about 67.6%, 79.1% and 36.46%, respectively. According to [PERSON] et al. [19], _Centella asiatica_ can remove 98% of NH\({}_{3}\)-N from wastewater. A medicinal plant such as _Centella asiatica_ can serve as phytoremediation agent as it has the ability to absorb different concentrations of contaminants in wastewater [47]. _Centella asiatica_ can accumulate heavy metals through its roots, stems and leaves [48; 49]. The roots of _Centella asiatica_ play an important role in this study which the roots trapped the suspended particles in wastewater sample. At the beginning of the phytoremediation treatment, the average reading of NH\({}_{3}\)-N was high. This is due to the decomposition of organic solid matter by the existing bacterial reaction in the sewage wastewater sample [50; 51]. Ammonia is one of the important nutrients for _Centella asiatica_ to grow. The reduction in pollutants such as TSS, NH\({}_{3}\)-N and COD in this study showed that sewage wastewater can be treated using _Centella asiatica_. The one-way ANOVA analysis conducted showed that there was a significant difference (\(p<0.05\)) in the reduction rate of the selected parameters. Based on the percentage of reduction as shown in Figure 5, it can be observed that _Ipomoea aquatic_ was more efficient in reducing the contents of TSS and NH\({}_{3}\)-N, while _Salvinia minima_ was more efficient in accumulating COD in the sewage wastewater sample. In a study conducted by [PERSON] et al. [52], _Ipomea aquatic_ was found to be more efficient than _Centella asiatica_ by its ability to accumulate higher concentration of aluminum (Al) and iron (Fe). [PERSON] et al. [19] found that _Centella asiatica_ was the most efficient for NH\({}_{3}\)-N removal compared to _Pistia stratiotes_, _Salvinia molesta_, _Ipomea aquatica_ and _Eichhornia crussipes_. It was indicated that each plant that acts as phytoremediation agent has its own efficiency rate in removing different pollutants. However, there are several factors that may affect the reduction percentage of contaminants, such as the type of pollutant and wastewater, treatment duration and pollutant concentration [52; 53; 54].