BIOSORPTIVE POTENTIAL AND BINDING SITES OF HEAVY METALS ON THE CELL WALL OF SELECTED FILAMENTOUS ALGAE

Abstract

Indiscriminate release of heavy metal pollutants into the environment from point and non-point industrial sources has posed a major threat to all kinds of organisms inhabiting aquatic and terrestrial habitats. The application of biosorption i.e., removal of heavy metal ions by the use of biomass, has emerged as a promising technique in the past few years. Utilization of green filamentous algae in this technology still remains largely unexplored. In the present study, the biosorption capacities of biomass of filamentous green algae, Spirogyra cummunis, Cladophora delmatica, and Spirogyra spp. were evaluated for toxic heavy metals, such as Cadmium, Cd (II) and hexavalent Chromium, Cr (VI). The biosorptive binding sites were studied with the help of Scanning Electron Microscopy (SEM) and Fourier Transform Infra-red Spectrometer (FTIR). Results revealed that the rate and extent of uptake were influenced by pH, contact time, and biosorbent concentration. The optimum pH value for uptake of Cd (II) was found to be 5.0 and that of Cr (VI) 4.0 by all the studied biosorbents. The equilibrium sorption data for Cd (II) at pH 5.0 and that of Cd (II) at pH 4.0 were described by various adsorption isotherms, such as Langmuir, Freundlich, and Temkin models. Langmuir isotherm was found to be the best suited for the interpretation of acquired data, showing monolayer adsorption and Freundlich theorem, the worst. Values of Cd (II) sorption capacity, (qmax) for the studied species were found to be 1.44, 11.9 and 14.42 and those of Cr (VI) were 498, 411 and 312, respectively. Kinetic and thermodynamic parameters were also studied. The results showed that pseudo-second order kinetics was suitable for the interpretation of data and thermodynamically biosorption was found to be feasible and spontaneous under the given conditions, in case of all the biosorption investigations undertaken in the present study. SEM and FTIR revealed biosorptive binding sites and possible electronegative functional groups, such as carboxyl, hydroxyl, carbonyl, etc., on the surface of biosorbents which could favor the binding of cations, such as Cd (II) and Cr (VI) ions.