Browsing by Author "Surya Kant Mehta"

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Characterization and optimization of Ni and Cu sorption from aqueous solution by Chlorella vulgaris
(2001) Surya Kant Mehta; Jai Prakash Gaur
Sorption of Ni and Cu by Chlorella vulgaris showed the second-order rate kinetics. Change in biomass concentration altered the kinetic parameters of sorption. When biomass concentration was increased from 5 to 1000 mg 1-1, the initial rates of sorption of Ni and Cu were reduced by about five- and three-times, respectively. The metal sorption capacity of the test alga was studied taking different concentrations of Ni and Cu at different biomass concentrations as well as different pH. The sorption of test metals fitted better in Freundlich than the Langmuir model thereby indicating multi-layer adsorption of Ni and Cu onto C. vulgaris. The Kf and Qmax both decreased with increase in biomass concentration thereby suggesting that the metal sorption capacity of the test alga was impaired at higher biomass concentrations. The maximum sorption of Ni and Cu occurred at pH 5.5 and 3.5, respectively. Heat-killed cells showed a greater potential of metal sorption than the live cells. The test alga was subjected to different pre-treatments to enhance its metal sorption capacity; acid (HCl and HNO3) pre-treatments were most effective. The maximal removal of Ni and Cu, 93 and 96%, respectively, occurred from solutions having their 2.5 mg 1-1 concentration. Thus C. vulgaris has a great potential for removing Ni and Cu especially when concentrations of these metals are low in the external environment. © 2001 Elsevier Science B.V. All rights reserved.
Recovery of uptake and assimilation of nitrate in Scenedesmus sp. previously exposed to elevated levels of Cu2+ and Zn2+
(Elsevier GmbH, 2004) Bhumi Nath Tripathi; Surya Kant Mehta; Jai Prakash Gaur
A study of the effects of elevated levels of Cu2+ and Zn 2+ on NO3- uptake and nitrate reductase (NR) activity in Scenedesmus sp. was carried out. The two metals inhibited NR and NO3- uptake in a concentration-dependent manner, with the latter process being inhibited more strongly than the former. After withdrawal of metal stress, NR activity and NO3- uptake recovered in a metal ion concentration-dependent manner. Dark pretreatment of the alga enhanced the toxic effects of the metal ions on NR activity and NO 3- uptake. The recovery from metal stress was slower in the dark-pretreated cells in comparison to the light-pretreated cells. No recovery of NR and NO3- uptake occurred in the presence of the photosynthetic inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), suggesting that photosynthesis was required for the recovery from metal stress. Cycloheximide blocked the recovery of NR activity in metal-treated alga, suggesting that new enzyme synthesis was required for the recovery from metal stress.
Removal of Ni and Cu from single and binary metal solutions by free and immobilized chlorella vulgaris
(Elsevier GmbH, 2001) Surya Kant Mehta; Jai Prakash Gaur
The potential of calcium alginate-entrapped Chlorella vulgaris in removing Ni and Cu from single and binary metal solution was determined. Almost complete removal of test metals from the solution by Chlorella beads (biomass concentration, 100 mg dry weight I-1) was achieved within 1 h when metal concentration was <10 mg l-1. The metal sorption capacity of free and immobilized biomass from binary metal solution was also determined using 3-D plots. The presence of the secondary metal (Cu and Ni) inhibited the sorption of the primary metal (Ni and Cu) by free as well immobilized cells but inhibition in sorption of Ni due to Cu was stronger than inhibition of Cu sorption by Ni. The total metal (Ni + Cu) sorbed from the binary metal solution by free as well as immobilized cells always remained lower than the total sorption of individual metals from their respective single metal solutions, thereby suggesting competition between Ni and Cu for the common binding sites on Chlorella. Better fitness of equilibrium metal sorption data to the Freundlich than the Langmuir model suggests multilayer adsorption of test metals onto the cell surface. Higher Kf and qm (Freundlich and Langmuir constants, respectively) for Cu than Ni sorption suggested that the test alga has a greater affinity for Cu than for Ni. It may be possible to use Chlorella beads for complete removal of Ni and Cu from dilute solutions having their concentrations below 10 mg l-1.