Comparison of biosorption and phytoremediation of cadmium and methyl parathion, a case-study with live Lemna gibba and Lemna gibba powder

• The Lemna gibba powder sorption.
• The overall adsorption is a physicochemical reaction.
• Sorption onto Lemna powder is governed by the film diffusion.
• Toxicity and the phytoremediation (phytodegradation) possibility combined to the adsorption process.

Heavy metals and pesticides can be adsorbed by several biomasses such as living or non-living aquatic plants. In this study adsorption properties of live Lemna gibba and Lemna gibba powder were investigated with regard to cadmium and methyl parathion (MP). Toxicity data (IC50) on live L. gibba indicated that the period of four days was adequate for phytoremediation. Initial adsorption studies showed that both adsorbents were capable of removing cadmium and methyl parathion. Cadmium and methyl parathion adsorption onto L. gibba powder was fast and equilibrium was attained within 120 min. The adsorption data could be well interpreted by the Freundlich model. The KF were: 7.8963 (Cd2+/ live Lemna); 0.7300 (MP/live Lemna); 11.5813 (Cd2+/Lemna powder); 1.1852 (MP/Lemna powder) indicating that Cd2+ was more efficiently removed by both biosorbents than MP. Adsorption kinetics for cadmium and methyl parathion in both systems and rate constants were determined for each contaminant. It was found that the overall adsorption process was best described by pseudo-second-order kinetics. Boyd model and external mass-transfer expression were tested. It was concluded that cadmium and methyl parathion sorption onto Lemna powder is governed by film diffusion.