## 4 Discussion  
Turbidity is the cloudiness of water [23] that occurs as a result of suspended materials, such as clay, silt, organic material, plankton, and additional particulate materials found in water [24]. The present study evaluated the turbidity reduction efficiency in the phytoremediation process of domestic wastewater using _P. stratiodes_, _S. molesta_, and _E. crassipes_ aquatic plants for a duration of 2 weeks with different retention times of 6, 12, and 24 h. After the 14-day phytoremediation process, the overall average turbidity values for the _P.-stratiodes-_, _S.-molesta-_, and _E.-crossipes_-treated wastewater samples with a 6 h retention time were recorded as 7.58 NTU (_P. stratiodes_), 12.82 NTU (_S. molesta_), and 9.61 NTU (_E. crassipes_) relative to the overall average influent turbidity value of 22.8 NTU. The overall average turbidity values for _P. stratiodes, S. molesta_, and _E. crassipes_ with a 12 h retention time were found to be 9.97 NTU, 6.17 NTU, and 9.80 NTU, respectively, relative to the overall average influent turbidity value of 28.9 NTU. Furthermore, the average turbidity values for the _P.-stratiodes-_, _S.-molesta-_, and _E.-crossipes_-treated water samples with a retention time of 24 h were found to be 7.1 NTU, 3.7 NTU, and 5.93 NTU, respectively, relative to the overall average influent turbidity value of 34.9 NTU. In the overall experiment, a turbidity reduction efficiency of the influent wastewater samples of up to 93.9% was attained in the course of this study. These findings showed that _P. stratiodes, S. molesta,_ and _E. crassipes_ plants were effectual at refining the water quality properties of the secondary treated domestic wastewater. The ideal conditions for the effective reduction of the turbidity level for this present study were found in the _S. molesta_ treatment systems with a retention time of 24 h; it was observed that the strength of the _S. molesta_ plants regarding absorbing the excess nutrient declined when the retention time was decreased to 12 and 6 h. Furthermore, during the 14-day sampling period, the roots were observed to hold and filter the suspended solids through a process known as rhizfiltration. This action was possible due to the long hairy roots of the selected test plants. Root hairs carry an electrical current that draws in suspended solids, resulting in them being committed to the roots, where they are gradually digested and assimilated by the plants [25]. Furthermore, the shallow system of the hydroponic method of phytoremediation process used in this study played a key role in improving the clarity of the wastewater because it provided a conducive environment for the trapped suspended particle sediment at the ground level of the pond. At the same time, the polished/filter water stayed at the upper level of the pond. These findings showed that the selected plants were efficient at refining the water properties of the secondary treated domestic wastewater to the permissible Malaysian water standard of class I (5 NTU) from the 10 th day to the final day of the sampling period with a retention time of 24 h. [PERSON] [26] reported up to an 85.66% improvement of turbidity in the phytoremediation of kitchen wastewater by _P. stratiodes_ after 10 days of retention time. Furthermore, [PERSON] and [PERSON] [27] indicated that _E. crassipes_ improved the wastewater quality significantly, as up to an 86.75% turbidity reduction was achieved in the treatment of kitchen wastewater samples during the 4-week study period. For the phosphate reduction analysis, with a 6 h retention time, overall average phosphate reductions of 3.97 mg/L (_P. stratites_), 4.29 mg/L (_S. molesta_), and 3.65 mg/L (_E. crassipes_) were obtained relative to the average phosphate level of 5.08 mg/L of the influent wastewater samples. For the 12 h retention time, overall average phosphate concentrations of 4.38 mg/L (_P. stratites_), 4.11 mg/L (_S. molesta_), and 2.5 mg/L (_E.