Phytoremediation of Nickel (II) Ions by Floating Aquatic Plants

Heavy metal pollution is a global issue that requires a proper solution as it can have adverse effects on human health. Conventional techniques for removing the heavy metals from wastewater are costly and environmentally unfriendly. Phytoremediation using floating aquatic plants is one of the cost-effective and promising ways to treat heavy metals in wastewater. However, the cultivation conditions of various types of floating aquatic plants need to be further investigated as information on this technique is very limited. The objective of this research is to develop a novel technique for the removal of heavy metals (Nickel (II) ions) by the phytoremediation technique using four floating aquatic plants (Salvinia natans, Pistia stratiotes, Eichhornia crassipes, and Salvinia auriculata) with a high reproductive rate. A comparative analysis was conducted by studying the cultivation conditions of these species and the kinetics of nickel (II) phytoremediation. In addition, parameter studies on the effect of solution pH, initial concentration of Nickel (II) Ions, and addition of a chelating agent on the phytoremediation efficiency were performed. From the study of surface morphology, two species belonging to the Salviniaceae family with numerous thin and tiny extended roots were found to be beneficial for phytoremediation. The uptake ability of the heavy metal by the floating aquatic plants followed the trend: P. stratiotes < E. crassipes < S. auriculata < S. natans. Optimal cultivation conditions were found to be at pH 7–8, 4 mg/L nickel (II) ions and 0.1 mg/L ethylenediaminetetraacetic acid (EDTA) as chelating agents to remove 93.52% of nickel (II) ions by Salvinia natans after seven days. The phytoremediation of nickel (II) ions using Salvinia natans could be well-described by the pseudo-second kinetic model. In conclusion, phytoremediation by floating aquatic plant was applicable to remove nickel (II) ions from wastewater.