Biosorption and desorption studies of chromium (III) by free and immobilized rhizobium (BJVr 12) cell biomass

Abstract

Experiments with free cell biomass (cells + exopolysaccharides) of Rhizobium BJVr 12 (mungbean isolate) showed that amount of Cr3+ ion sorbed is influenced by the amount of biomass to Cr3+ concentration ratio and time of contact. A ratio of 0.5 g fresh biomass to 10.0 ml 5.03 ppm Cr3+ sorbed 0.0275 mg Cr equivalent to an uptake of 2.86 mg Cr g-1 dry biomass and 1.0 g: 10.0 ml sorbed 0.0366 mg Cr equivalent to an uptake of 1.9 mg Cr g-1 biomass. Immobilized cell biomass in ceramic beads and in aquacel (a porous cellulose carrier with a charged surface) were more efficient than free cell biomass in adsorbing Cr(III). A reduction of 49.7% of Cr(III) for free cells, 95.6% for cells immobilized in ceramic beads and 94.6% for cells in aquacel was achieved after 48 hours under shaken conditions. Sorption capacities of immobilized cell biomass in ceramic beads and aquacel ranged from 5.01 to 5.06 mg Cr g-1 dry cell biomass. The biosorption of Cr3+ follows generally the Langmuir and Freundlich models of adsorption at low Cr3+ concentrations. The Langmuir constant for immobilized cells in ceramic beads are: Q0, 0.065 mmol Cr g-1 biomass; b (affinity constant), - 694 1 mmo1-1 Cr and for cells in aquacel Q, 0.07 mmol Cr g-1 biomass; b, - 694 1 mmol Cr g-1 Cr. The Freundlich constants are: K, 0.071 mmol Cr g-1 biomass; n, 0.13 g-1 biomass 1-1 and for aquacel: K, 0.074 mmol g-1 biomass; n, 0.13 g-1 biomass. Biotraps made up of immobilized cells in ceramic beads and aquacel were tested for adsorbing Cr(III) using two different flow rates: 0.5 ml/min and 1.5 ml/min. A significantly higher amount of Cr(III) was adsorbed at the lower flow rate of 0.5 ml/min. Biosorption of Cr3+ is competitive. The treatment of a waste water sample containing 6.03 ppm Cr3+ and other cations with the biomass reduced the Cr3+ concentration to that much lower than for the test solution containing only Cr. Recovery of biosorbed Cr(III) was by treatment at a different pH using dilute HCl solution. Recovery was higher for cells imbibed in ceramic beads than aquacel. Percentage recoveries for cells in aquacel are 46.4% at pH 1.0, 33.0% at pH 3.0 and 6.6% at pH 6.0-7.0. For cells in ceramic beads, percentage recoveries are: 93.1% at pH 1.0, 75.6% at pH 3.0 and 16.4% at pH 6.0-7.0. Biosorption of Cr3+ by cells immobilized in ceramic beads is reversible but only partially for cells in aquacel.

Source or Periodical Title

Biodegradation

ISSN

9239820

Page

275-285

Document Type

Article

Subject

Biosorption of Cr(III), Biotraps, Desorption, Rhizobium cells

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