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Study of the Biosorption of Cd(II) from Aqueous Solution by Biomass Bacillus sp. Isolated from Desert-Maranjab Soil

 

Salman Ahmady-Asbchin, University of Ilam, Ilam, Iran

Naser Jafari, University of Mazandaran, Babolsar, Iran

 

Abstract

Microorganisms play a vital role in heavy metal contaminated soil and wastewater by the mechanisms of biosorption. The first reports described how abundant biological materials could be used to remove, at very low cost, even small amounts of toxic heavy metals from industrial effluents. Biosorption of toxic metals can be an effective process for the removal and recovery of heavy metal ions from aqueous solutions. The objective of this research was to isolate microorganisms which produce uptake of Cadmium ions, from soils in Desert-Maranjab. In this study various soil samples were collected in Desert Maranjab and were cultured on nutrient agar and saboroud dextrose agar and the patent isolates were purified. Twenty soil samples were collected from various areas of Desert-Maranjab, Iran. Initial screening of a total of 40 bacterial isolates at pH 5, resulted in the selection of one isolate with maximum uptake capacity of cadmium ions 0.62 mmol/g dry weights. It was tentatively identified as Bacillus sp. according to morphological and biochemical properties and named strain AEJ-89. This Bacillus sp. gram positive bacteria were used to investigate the biosorption of cadmium ions. In the next step the effects of some ecological parameters (temperature, pH, kinetics and isotherm were studied on the biosorption. The equilibrium time was about 5 min and the adsorption equilibrium data were well described by the Langmuir`s equation.

 

Keywords: biosorption, Desert-Maranjab, cadmium, uptake, bacterium

 

1. Introduction

Heavy metals, especially at trace concentration in a large volume of solution, are considerably difficult to remove by conventional techniques such as chemical precipitation of metals (changing the pH), reverse osmosis and other methods. The need for an economic and effective method for the removal of heavy metals has resulted in the development of new separation technologies. Bacteria are quite adequate for heavy metals biosorption due to their ability to adsorb metal ions, suitability for natural environments and low cost. The surface envelopes of bacterial cells can adsorb various heavy metals by virtue of ionic bonds to their intrinsic chemical groups. The sites for metal binding are different according to bacterium species and metals. The discovery and development of biosorption phenomena provide a basis for a whole new technology aimed at removal of heavy metallic species from dilute solutions in the range of 1 to 100 mg/L. Recovery of some of these metals is a possibility. Biomass from various natural or industrial origins can be used as complexing materials to recover toxic or strategic elements from industrial wastewaters. The major mechanisms responsible for it include ionic interactions and complex formation between metal cations and ligands contained in the structure of the biomaterials. However, very little is known about the actual tissue structure and composition of different organisms, which also vary widely depending on the growth conditions for industrial or laboratory grown biomass, and the location or the season for natural harvested biomass. The unknown features of most biosorbents reduce their chance to be used as competitive products compared to well-known synthetic ion exchangers, even if their costs are expected to be significantly lower. The knowledge of the chemical structure of biosorbents is essential for modeling and predicting their metal binding performance in water purification systems.

 

2. Materials and methods

 

Biomass production

Twenty soil water samples were collected from the Desert Maranjab in Isphahan province. It is situated between 34°16' 54" North latitude and 51°48'16" East longitude in the Isphahan region of Iran. The bacterial strain Bacillus sp. was isolated from Desert Maranjab soil. The bacterial strain was isolated on nutrient agar medium comprising (g/l): bacteriological peptone, 5.0; sodium chloride, 8.0; beef extract, 3.0, agar, 2% and pH 7.0. Pure bacterial culture was obtained by repeat streaking on basal agar medium using standard isolation techniques. For isolation, inculcated plates were incubated at 37°C for 72 h. The pure colony was obtained and identified from microbial type culture collection, University of Ilam.

 

Preparation of bacterial biosorbents

For biosorption study, bacterial strain Bacillus sp. was cultivated aerobically in 250 ml Erlenmeyer flask containing sterile nutrient broth on a rotary shaker 130 rpm at 37°C. Cells were harvested at the end of experimental phase. After cultivation, the cells were centrifuged at 10.000×g for 20 min and then washed three times with deionized water and wet weight of the cells equivalent to 0.8 g dry weight/L was used in the experiments.

 

Table1

Morphological, physiology and biochemical characteristics of Bacillus sp. strain AEJ-89

 

 

 

Biosorption studies

In terms of initial pH of solution impacts on biosorption, the cadmium concentration of working solution was selected at 10 mg/L, and 1 mol/L NaOH and 1 mol/L HCl were used to regulate the initial pH to the investigating range, from 1.1 to 7.8 standard values. The determination of the equilibrium time of cadmium removal was carried out with three working solutions with the same pH at 4.8 and different cadmium concentration, 50, 200, and 400 mg/L. Samples via reaction for 1, 2, 3, 4, 5, 10, 20, 30, 60, 90, and 120 min would be analyzed to determine the equilibrium time. In addition, metal solutions with various concentrations ranging from 50 to 500 mg/L were used to assess the effect of initial metal ion concentration on biosorption. Metal analysis was carried out by an inductively an, atomic absorption spectrometer (Chem., Tech, Analytical CTA 2000). The metal adsorption uptake (q, mg/g) was calculated with Eq.

 

  

where V (L) is the volume of solution in flask, C₀ (mg/L) is the initial metal concentration, C_e (mg/L) is the residual metal concentration, and W (g) is the weight of adsorbent.

 

3. Results and discussion

Because pH is one of the main controlling parameters affecting the  adsorption process, the biosorption of cadmium on Bacillus sp. were measured at initial cadmium concentration of 100 mg/L, with pH ranging from 1.0 to 7.8 (Fig.1). The increase of pH has a positive effect on metal uptake. The maximum adsorption of cadmium ions on Bacillus sp. was observed at pH 5.2.

 

Fig. 1. Effect of pH on cadmium biosorption by biosorbent

 (initial concentration 100 mg/L; biosorbent concentration 1 g/L; 25°C; 150 r/min)

 

Effect of initial cadmium concentration is graphically shown in Fig 2. The increase of biosorbent concentration caused a decrease in the metal specific uptake and an increase in the biosorption removal efficiency. Indeed, the specific uptakes dropped from 142 to 61 mg/g biomass and the biosorption removal efficiency increased from 71.2 to 91.2%, respectively, as the biomass dose increased from 500 to 1500 mg/L. Such a trend is mainly attributed to an increase in the sorptive surface area and the availability of more adsorption sites.

 

Our results suggest that Bacillus sp. biomass could be an interesting biosorbent for cadmium removal from aqueous solutions.

 

 

Fig. 2. Effect of initial cadmium concentration on removal efficiency by Bacillus sp.

 (biosorbent concentration 1 g/l; 25°C, 150 rpm)

 

Acknowledgments

This research was supported by the Ilam University of Iran.

 

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Salman Ahmady-Asbchin, Assistant Professor, Department of Biology, Faculty of Science, University of Ilam, Ilam, Iran. Tel./ fax +98 (841) 223-48-60. E-mail
 

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