Bioremediation of Cu(II) contaminated water by Saccharum ofcinarum: effect of oxalic acid modifcation on equilibrium, kinetic and thermodynamic parameters
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Date
2016
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Abstract
Background: Copper is one of the heavy metals whose presence in aquatic environment in higher concentration
poses a major threat to the environment. This is due to their toxic effects on the plants, animals and human health.
Biosorption an innovative biotechnological technique with superior advantages was used for the remediation of Cu2+
from aqueous solution in this study.
Methods: Biosorbent was prepared from raw (RAWB) and oxalic acid modifed (OAMB) Saccharum ofcinarum. They
were characterized by scanning electron microscopy (SEM/EDAX), fourier transform infrared (FTIR), and X-ray diffraction (XRD) for surface morphological study. Experimental data obtained from batch equilibrium studies were subjected to two-parameters [Freundlich, Langmuir, Tempkin and Dubinin–Radushkevich (D–R)] and three-parameter
[Redlich–Peterson (R–P), Sips, Hill and Toth] isotherm models. Kinetic data were analysed with pseudo frst-order,
pseudo second-order, Elovich and Avrami kinetic models.
Results: The results of proximate analysis and characterization show that the oxalic acid modifcation affected the
biosorbents content, surface modifcations and the functional groups present. The experimental data from the equilibrium studies were best ftted to the isotherms with R2 >0.9 for the OAMB and RAWB. The adsorption energies (E)
from the D-R isotherms were found to be 0.36 and 0.06 kJ/mol for OAMB and RAWB respectively, which is indication
of physisorption favoured processes. Pseudo second-order model best ftted the data with a coefcient of determination (R2) of above 0.998 with an average relative and hybrid errors lower than 5 %. Intraparticulate diffusion model
analysis showed that the adsorption process develops in two stages as rapid and slow phase. Changes in standard
free energy (∆G°), enthalpy (∆H°) and entropy (∆S°) for the biosorption processes were estimated using the thermodynamic equilibrium model. The calculated thermodynamics parameters indicated that the process is spontaneous and
endothermic in nature.
Conclusions: This study revealed the feasibility of Cu2+ removal through biosorption processes using S. ofcinarum
biomass as biosorbent. The improved surface morphology for increase biosorption by oxalic acid modifcation is also
favourable. The biosorption process for the removal of the Cu2+ is pH dependent as the efciency increased from 36.4
to 65.3 % for raw biomass while the OAMB has increase efciency from 57.5 to 88.6 as the pH increases from 2 to 6.
Keywords: Saccharum ofcinarum, Oxalic acid, Biosorption, Kinetics, Thermodynamics, Equilibrium