## 3 Results and Discussion
### Removal of TSS, NH\({}_{3}\)-N and COD
#### 3.2.3 Reduction Rate of COD  
The graph of COD content reduction in sewage wastewater sample by phytoremediation treatment by _Lemma minor_, _Salvinia minima_, _Ipomoea aquatic_ and _Centella asiatica_ is shown in Figure 5. The average of initial reading for COD was about 96 mg/L. The reading of COD content was decreased on day 2 of treatment with the average value of 66.33 mg/L, 56.33 mg/L, 90 mg/L and 91 mg/L when treated with _Lemma minor_, _Salvinia minima_, _Ipomoea aquatica_ and _Centella asiatica_, respectively. The average of final COD value was approximately 24 mg/L, 17.33 mg/L, 53 mg/L and 61 mg/L for the phytoremediation by _Lemma minor_, _Salvinia minima_, _Ipomoea aquatica_ and _Centella asiatica_, respectively. The reduction in COD was obtained because the plants underwent the process of photosynthesis. The photosynthesis activity increases the dissolved oxygen in water, thus creating aerobic conditions in wastewater in favor of aerobic bacterial activity to reduce BOD and COD contents [34]. This can be an indication that wastewater would have a lesser impact on the environment after being treated using the phytoremediation method [35]. Figure 4: The average of NH\({}_{3}\)-N reading by the phytoremediation using _Lemma minor_, _Salvinia minima_, _Ipomoea aquatica_ and _Centella asiatica_. Figure 5: The average COD reading by the phytoremediation method using _Lemma minor_, _Salvinia minima_, _Ipomoea aquatica_ and _Centella asiatica_. 2.4. Phytoremediation Efficiency by _Lenna minor_, _Salvinia minima_, _Ipomoea aquatica_ and _Centrella asiatica_  
The results indicated that all plants used as phytoremediation agents in this study were able to reduce the TSS, NH\({}_{3}\)-N and COD contents in sewage wastewater samples with different rates of reduction. Figure 6 shows the percentage of reduction of the three parameters after the 8 days of phytoremediation treatment by _Lenna minor_, _Salvinia minima_, _Ipomoea aquatica_ and _Centrella asiatica_. Based on the results, _Lenna minor_ reduced about 50.8% of the TSS content. While the average reading of NH\({}_{3}\)-N was reduced by up to 80.4%. For COD content in the sewage wastewater sample, _Lenna minor_ able to absorbed approximately 75% of COD after 8 days of treatment. A one-way ANOVA test showed that there was a significant difference (\(p>0.05\)) in the contaminants reduction. According to [PERSON] and [PERSON] [18], _Lenna minor_ was able to remove COD and NH\({}_{3}\)-N by 93.7% and 66.4%, respectively. [PERSON] et al. [36] found that _Lenna minor_ reduced the TSS content by 96.3%. _Lenna minor_ has been reported as a highly efficient floating macrophtye in organic pollutant removal [37; 38]. As for _Salvinia minima_, the results showed that after 8 days of treatment, this plant had reduced the content of TSS, NH\({}_{3}\)-N and COD by 77.6%, 89.9% and 82%, respectively. The ANOVA analysis conducted shows that there was a significant difference (\(p>0.05\)) in the reduction reading of pollutants. _Salvinia minima_ is a fast-growing aquatic fern which has high adaptability to various aquatic environments [39; 40; 41]. Salvinia minima was able to accumulate pollutants in different physiological conditions, as it consists of floating leaves and a submerged leaves structure [42; 43]. According to [PERSON] et al. [44], their study indicated that _Salvinia minima_ was more effective compared to _Spirodela polyrrhizza_ in the phytoremediation of high-strength organic wastewater at a maximum initial NH\({}_{3}\)-N concentration of 70 mg/L and at a pH of 6. [PERSON] et al. [45] reported that _Ipomoea aquatica_ can accumulate up to 80% of TSS, 36.3% of COD and 30% of NH\({}_{3}\)-N in palm oil mill wastewater. In this study, 85.6% of TSS was removed by _Ipomoea aquatica_ after the phytoremediation treatment of sewage wastewater for 8 days. _Ipomoea aquatica_ was able to trap TSS because of its larger and longer root structure with a lot of hair. Ammonia is one of the nutrients that macrophytes need to survive.