## 4 Discussion
crassipes_) were observed for the 24 h treatment systems relative to the average ammoniacal nitrogen level of 21.26 mg/L of the influent wastewater samples. Additionally, the maximum ammoniacal nitrogen reduction percentages for the _P. stratites_, _S. molesta_, and _E. crassipes_ treatment systems were found to be 88.66%, 90.47%, and 89.11%, respectively, on the 14 th day of the experiment with a 24 h retention time. Therefore, the overall trend of the reduction efficiency for the three treatment systems was in the pattern of 24 h \(>\) 12 h \(>\) 6 h. As such, the findings obtained from this present indicated that the 6 h retention treatment was not ideal or efficient for the selected test plants to take up a substantial amount or break down the ammoniacal nitrogen present in the influent wastewater samples. This could be attributed to the short contact time observed in the 6 h treatment systems. Furthermore, plants take up nutrients through both direct (i.e., plant uptake) and indirect (microbial activity at rhizosphere) ways; plants play a significant role in absorbing ammoniacal nitrogen from wastewater. For plant uptake to support biomass growth and development, ammoniacal nitrogen present in wastewater can be directly absorbed by roots, either via accumulation in the plant parts or assimilation by the plant in nitrogen-transported amino acids [32; 33]. By way of the acceleration of nitrogen decomposition in the rhizosphere, an enhancement of other elements' activity, and an improvement in bioavailability, microbial activity is another major route to remove nitrogen through plant uptake [34]. Additionally, the results obtained from the 12 and 24 h retention time scenarios corroborates with the findings reported by [PERSON] et al. [35], who reported an up to 84.8% ammoniacal nitrogen reduction from sewage wastewater by _P. stratites_. Furthermore, [PERSON] and [PERSON] [27] recorded an up to 94.36% removal of ammoniacal nitrogen from kitchen wastewater samples using _E. crassipes_. For the nitrate analysis, the overall results showed that the three tested aquatic plants were effective at removing nitrate from the wastewater samples. For the 6 h retention time, overall average nitrate reductions of 2.74 mg/L (_P. stratites_), 4.1 mg/L (_S. molesta_), and 3.47 mg/L (_E. crassipes_) were found relative to the average nitrate level of 7.05 mg/L of the influent samples. For the 12 h retention time, the overall average nitrate concentrations of 3.6 mg/L (_P. stratites_), 2.71 mg/L (_S. molesta_), and 3.45 mg/L (_E. crassipes_) were recorded relative to the average nitrate concentration of 8.52 mg/L of the influent samples. Overall average nitrate reductions of 4.03 mg/L (_P. stratites_), 4.85 mg/L (_S. molesta_), and 3.95 mg/L (_E. crassipes_) were observed for the 24 h treatment systems relative to the average nitrate concentration of 12.05 mg/L of the influent samples. Among the three wastewater treatment (6, 12, and 24 h) systems, the 24 h retention system showed a better performance in the nitrate uptake compared to the 6 and 12 h retention time treatment systems. Furthermore, the outcome of this research demonstrated that _E. crassipes_ and _S. molesta_ plants exhibited higher efficiencies regarding nitrate uptake relative to _P. stratites_ plants at 12 and 24 h retention times. Similarly, rapid growth was observed in all three test plants, which contributed to the high nitrate uptakes into the plant roots in the 12 and 24 h treatment systems. For the 12 h treatment system, _S. molesta_ (82.90%) performed better than _E. crassipes_ (68.38%) and _P. stratites_ (68.06%). The trend of the nitrate reduction efficiency for the three test plants with a retention time of 6 h was in the order of _P. stratites_\(>\)_E. crassipes_\(>\)_S. molesta_. Furthermore, it was observed that the water quality of the influent nitrate concentration was improved to class I by the test plants from the 6 th day to the 14 th day of the sampling period with a 24 h retention time.