Toxic cadmium removal from water effluents by Rhizobium sp. (BJVr-12) Extracellular Polysaccharides (EPS)

Issue Date

1999

Abstract

Cadmium is one of the "big three" toxic metals (mercury, lead, and cadmium) well recognized for their deleterious effects on the environment.

The capacity of coconut husk-immobilized Rhizobium sp. (BJVr-12) cells to adsorb Cd²⁺ from aqueous solutions was studied. A maximum of 98.7% removal of Cd²⁺ or 0.3 mg. Cd²⁺ gˉ¹ cells was observed after two hours of elution at a flow rate of one milliliter per minute.

The optimum flow rate for adsorption was determined by passing a solution containing 30 ppm Cd²⁺ ions through the column at different flow rates. The slower flow rate (1 ml/min) gave the highest adsorption.

The biosorption of Cd²⁺ generally follows the Langmuir model of adsorption at low metal concentrations. The Langmuir constants for immobilized cells (EPS) in coconut husk are: Qo = 0.04 mMCd (II) gˉ¹ biomass; b = 19.42 mMˉ¹ Cd (II)gˉ¹.

The Freundlich constants are K = 0.7221 mM Cd(II) gˉ¹ biomass; n = -1.4296 gˉ¹ biomass Lˉ¹, while those for the coconut husk alone are Qo = 0.0023 mM Cd²⁺ gˉ¹ biomass b = -942.64 mMˉ¹ Cd²⁺ gˉ¹ and K = 0.2916 mM Cd²⁺ gˉ¹ biomass and n = 18.027 gˉ¹ biomass Lˉ¹. High values for Qo and K suggest many available binding sites for Cd²⁺ on the bacterial surface. High values for b and n suggest high affinity of the biomass for Cd²⁺.

Recovery of the biosorbed cadmium from the biotraps using hydrochloric acid (6 M HCI) and citric acid (o.3 mM) was also studied. Results showed that hydrochloric acid desorbed 0.3396 mg Cd (II) per 30 ml (72% Cd²⁺ desorption) compared to citric acid which only desorbed 0.0833 mg Cd(II) per 30 ml (25% Cd²⁺ desorption).

Source or Periodical Title

Journal of Environmental Science and Management

ISSN

0115-463x

Volume

2

Issue

1

Page

17-26

Document Type

Article

Frequency

semi-annually

Physical Description

diagrams, graphs, tables

Language

English

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