Title of Thesis
Biosorption of Heavy Metals (Cr, Ni and Pb) by
Department of Botany / University of the Punjab,
|Number of Pages|
|Keywords (Extracted from title, table of contents and
abstract of thesis)|
Biosorption, Heavy, Metals, Cr, Ni, Pb Immobilized, Microalgae, loofa,
sponge, equilibrium, microalgal, adsorption, desorption
A unique immobilized disc biosorbent was developed by entrapping an indigenous microalgal strain of Chlorella sorokiniana onto a fibrous network of loofa sponge using a novel technique of immobilization and evaluated as a new biosorption system for the removal of heavy metals (chromium. nickel and lead) from aqueous solution.
The loofa immobilized biomass of C. sorokiniana (LIBCS) disc biosorbent removed heavy metals very efficiently with maximum metal removing capacity of 68.=1. 59.58 and 121.29 mg g-1 biosorbent for chromium(III), nickel(II) and lead(II) at equilibrium, respectively. These values were 17.26, 23.01 and 15.07% higher than the amount of chromium(Ill), nickel(II) and lead(II), respectively, removed by free biomass of C sorokiniana (FBCS) under the identical conditions. During these biosorption studies, LIBCS exhibited excellent physical and chemical stability without any significant release/loss of microalgal biomass from loofa sponge matrix.
Biosorption of all three metals by LIBCS was found to be pl-I dependent and the maximum adsorption was noted at a solution pH 4-5. The biosorption of metal ions by LIBCS increased as the initial concentration of metal ions increased in the medium. The kinetics of metal removal by LIBCS was extremely fast;reaching equilibrium in about 15 min. The biosorption equilibrium perfectly fit the Langmuir adsorption
isotherm model with 0.99 regression coefficient(r2) for all three metals. The fit on Freundlich adsorption isotherm model was acceptable but not as good. The pseudo-firs: and second order kinetic models were also applied to the experimental data. The
sorption data for all three metals was found to follow the second order kinetic model with r2
of 0.99. The first order was not applicable to the data. The metal removing capacity of LIBCS was also tested in continuous flow fixed-bed column bioreactors and was found to be highly effective in removing chromium(III), nickel(II) and lead(II) from aqueous solution. On plotting breakthrough curves it was noted that LIBCS in fixed bed column was capable of bringing down heavy metals concentration from 10 mg I-1 to 0.05, 0.02 and 0.1 mg I-1 for chromium(III), nickel(II) and lead(lI).respectively, well below from the WHO limits for drinking water. The LIBCS was regenerated using dilute solution of HCI for lead(II) and nickel(II), with up to 99% recovery and dilute HNO3 for chromium(III), with up to 9S% recovery. The LIBCS were shown to be robust and stable with 6.71%, 7.64% and 11.21% loss in the lead(II), nickel(II) and chromium(III) uptake capacity after seven adsorption-desorption cycles in batch experiments and only 4.97%, 6.10% and 7.32% loss in lead(ll), nickel(II) and chromium(Ill) sorption capacity, respectively, after five adsorption-desorption cycles in continuous flow fixed bed column operations. Biosorption of heavy metals was not affected in the presence of other light metals. In view of its possible practical application in the industrial wastewater treatment, metal removing potential of LIBCS was investigated for the removal of heavy metals from authentic wastewater, collected from a local electroplating industry. The LIBCS packed in fixed bed column bioreactor removed the metal ions from wastewater very effectively thus confirming the possibility of developing a biological treatment process for the removal of toxic metals from authentic wastewater.
The efficient metal removing ability of LIBCS in both batch flask experiments and continuous flow fixed bed column bioreactors, low cost of loofa sponge and simplicity of the immobilization technique used to produce the LIBCS biosorbent system suggest that this novel biosorbent could lead to the development of a viable and cost-effective technology for metal removal from industrial wastewaters containing heavy metals.