Authors:

Abstract

Owing to various anthropogenic activities our environment is being polluted especially by discharging effluents containing heavy metals. Heavy metals are non degradable and persist for a long time in the environment. Hence they pose potential risk on the environment. Cadmium is a toxic element and cause severe damages to both animals and plants. Biosorption which is a process that utilizes dead or living biomass to sequester heavy metals is currently gaining considerable important as an alternative low cost and eco-friendly technology to remove heavy metals from aquatic media. In this study, three aquatic plants such as Eichhornia crassipes, Ceratophyllum demersum and Salvinia mullets were screened for the biosorption of cadmium and the plant biomass was analyzed for Cd using Atomic Absorption Spectrometer. Ceratophyllum demersum was selected and batch experiments were carried out to examine the influence of biosorbent dosage, initial concentration of metal ion and contact time on the cadmium (II) ion adsorption. Sorption data was analyzed using linear and nonlinear regression methods of Langmuir and Freundlich isotherm models. Desorption experiment was also carried out. Biosorption of cadmium by Ceratophyllum demersum was very rapid (20 minutes) at pH 5 and at room temperature. Adsorption capacity of Ceratophyllum demersum for cadmium increased with increasing concentration of Cd ions. The nonlinear adsorption isotherm of Langmuir model did not fit well with the sorption data (high χ2 = 4.58). Although three linear forms (I, II and V) of Langmuir isotherm model supported the sorption data (R2=0.9316, 0.9124 and 0.912), however the separation factor, RL, was less than zero and also maximum adsorption capacity, qm were very low in all five linear forms. Both linear and nonlinear forms of Freundlich adsorption isotherm model exhibited a better fit with high correlation R2=0.92 and low χ2 = 1.95 respectively, which indicates a multilayer adsorption. Desorption experiments indicated that 0.1M EDTA, 0.1M HCl and 0.1M HNO3 were efficient desorbents for recovery of Cd (II) from the loaded biomass.

Journal of Environmental Professionals Sri Lanka: 2015 Vol. 4 No. 2: 10-24

Keywords: Biosorption, Cadmium, Ceratophyllum demersum, Isotherms models