## 3 Results
### Ammoniacal Nitrogen Reduction  
The results of the ammoniacal nitrogen analysis obtained from the biological treatment of domestic wastewater using _P. striatiotes_, _S. molesta_, and _E. crassipes_ aquatic weed plants for a 14-day duration with different retention times of 6, 12, and 24 h are represented in Figures 9-11, respectively. Figure 9: Bar plot of the average ammoniacal nitrogen vs. the sampling period with a 6 h retention time. From Figure 9, the ammoniacal nitrogen concentration of the influent wastewater samples from the STP was observed to be inconsistent throughout the sampling period and ranged from 12.8-23.89 mg/L. The results presented demonstrated that a slow reduction of the influent ammoniacal nitrogen level was recorded during the 14-day treatment. The ammoniacal nitrogen removal efficiencies with a 6 h retention time for _P. stratotes_, _S. molesta_, and _E. crassipes_ were within the ranges of 12.86-20.41%, 4.17-14.07%, and 4.04-35.92%, respectively. However, the _S.-molesta_-treated effluent samples showed a lower ammoniacal nitrogen concentration compared to the _P.-stratotes_- and _E.-crossipes_-treated wastewater samples. The performance of the influent samples compared to the individual test plants was found to be significant (_p_ < 0.05). Based on the results presented in Figure 10, it was found that the ammoniacal nitrogen concentration of the influent wastewater samples fell within the range of 13.4 to 21.86 mg/L. A gradual decrease was observed in the ammoniacal nitrogen reduction of the influent samples throughout the 14-day  
Figure 11: Bar plot of the average ammoniacal nitrogen vs. the sampling period with a 24 h retention time. Figure 10: Bar plot of the average ammoniacal nitrogen vs. the sampling period with a 12 h retention time. treatment process. Similarly, the ammoniacal nitrogen level of the influent sample was recorded as \(13.4\pm 0.1\) mg/L on the second day, which was slightly reduced to \(12.5\pm 0.1\) mg/L, \(13.04\pm 0.01\) mg/L, and \(10.1\pm 0\) mg/L by _P. striatiotes_, _S. molesta_, and _E. crassipes_, respectively. The changes showed small reduction efficiencies of 6.71% for _P. striatiotes_, 2.68% for _S. molesta_, and 24.6% for _E. crassipes_. However, after 10 days, a significant reduction in the influent ammoniacal nitrogen concentration was observed. On the 12 th day of the sampling period, the initial ammoniacal nitrogen value of \(23.2\pm 0.04\) mg/L was drastically reduced to \(8.0\pm 0\) mg/L, \(10.04\pm 0.01\) mg/L, and \(11.13\pm 0.05\) mg/L by _P. striatiotes_, _S. molesta_, and _E. crassipes_, respectively. On the 14 th day, the three test plants improved the concentration of the influent wastewater sample from \(21.86\pm 0\) to \(6.36\pm 0.05\) mg/L (_P. striatiotes_), \(8.01\pm 0.02\) mg/L _S. molesta_), and \(10.8\pm 0.1\) mg/L (_E. crassipes_). Furthermore, the ammoniacal nitrogen removal efficiencies with a 12 h retention time for _P. striatiotes_, _S. molesta_, and _E. crassipes_ were estimated to be in the ranges of 60-71%, 45-65%, and 36-50%, respectively, at the end of the 14-day treatment. _P. striatiotes_ performed better than _S. molesta_ and _E. crassipes_ at lowering the ammoniacal nitrogen concentration of the influent wastewater samples. Moreover, the performance of the influent samples compared to the individual test plants was found to be significant (\(p<0.05\)). Based on the results presented in Figure 11, it can be seen that the concentration of ammoniacal nitrogen in the influent samples varied during the sampling period. However, the effluent samples indicated a constant rate of reduction in the ammoniacal nitrogen compared to the influent samples from the beginning to the last day of the sampling period with a little inconsistency on the fourth day of the sampling period. Similarly, it was observed that _P.