## 4 Discussion
crassipes_) were recorded relative to the average phosphate level of 5.50 mg/L of the influent wastewater samples. Similarly, overall average phosphate reductions of 4.46 mg/L, 5.45 mg/L, and 2.92 mg/L were observed for the 24 h treatment systems relative to the average phosphate level of 11.01 mg/L of the influent wastewater samples. These results proved that the plants reduced the phosphate concentration of the influent samples to varying degrees. The intrinsic variances in macronutrient requirements for physiological processes may have attributed to the alterations detected by the three plants [28]. Similarly, a rise in phosphate levels during the sampling period was observed on the 10 th day with a 6 h retention time. However, the findings of this present study demonstrated that the treatment systems with 6 and 12 h retention times did not provide favorable conditions for the plant roots to absorb and assimilate the phosphates present in the wastewater samples. Thus, these findings strongly agree that retention time is a fundamental factor that determines and controls the rate at which nutrient absorption and assimilation by plants takes place in plant-based wastewater treatment systems. Furthermore, the overall results obtained from the three treatment systems (6, 12, and 24 h retention times) show that _E. crassipes_ displayed better properties regarding absorbing the excess phosphate concentration in the wastewater samples than the _P. stratites_ and _S. molesta_ plants. Furthermore, phosphorous is a macronutrient of plants. It is also a chief constituent in adenosine diphosphate (ADP) and adenosine triphosphate (ATP), which is critical for energy storage. It also aids in energy transfer in photosynthesis and respiration, and is essential in the formation of ADP and ATP, and the building of their biochemical structural components, such as the nucleic acids, nucleotides, and sugar building up their biomass [28]. Hence, a significant quantity of phosphate, or more precisely, free orthophosphate was taken up from the wastewater throughout the 14 days. Therefore, the phytoremediation systems helped to reduce the phosphate concentration in the water body significantly and steadily. Additionally, the reduction of phosphorous was similarly testified by many authors in other research works that found effective nitrogen and phosphorous removal by _E. crassipes_[29]. Furthermore, the results obtained from this study corroborate with the report of [PERSON] et al. [13], who stated that to treat phosphate in wastewater; _E. crassipes_ was the best plant among five species (_P. stratites_, _I. aquatic_, _S. molesta_, _C. asiatica_, and _E. crassipes_). Aquatic plant species have long fibrous roots that have the ability to provide an extensive surface area for the plant to carry out physical, chemical, and microbial processes for nutrient absorption and nitrification processes [30]. [PERSON] et al. [31] reported up to 82%, 83.3%, and 72.1% reductions in phosphorous by _E. crassipes_, _P. stratites_, and _S. molesta_ from Nile tilapia pond wastewater. For ammoniacal nitrogen reduction, the overall results demonstrated that an up to 80-90% ammoniacal nitrogen reduction was achieved by the cultivation of the test plants in wastewater samples. Similarly, overall average ammoniacal nitrogen reductions of 15.10 mg/L (_P. stratites_), 16.33 mg/L (_S. molesta_), and 14.76 mg/L (_E. crassipes_) were achieved relative to the average ammoniacal nitrogen of 18.23 mg/L of the influent wastewater samples with a 6 h retention time. For the 12 h retention time, overall average ammoniacal nitrogen reductions of 13.62 mg/L (_P. stratites_), 14.60 mg/L (_S. molesta_), and 14.26 mg/L (_E. crassipes_) were recorded relative to the average ammoniacal nitrogen concentration of 20.01 mg/L of the influent wastewater samples. Similarly, overall average ammoniacal nitrogen concentrations of 9.08 (_P. stratites_) mg/L, 9.05 mg/L (_S. molesta_), and 8.25 mg/L (_E.