Elsevier

Bioresource Technology

Volume 99, Issue 10, July 2008, Pages 4185-4191
Bioresource Technology

Removal of cadmium(II) ion from aqueous system by dry biomass, immobilized live and heat-inactivated Oscillatoria sp. H1 isolated from freshwater (Mogan Lake)

https://doi.org/10.1016/j.biortech.2007.08.068Get rights and content

Abstract

Oscillatoria sp. H1 (Cyanobacteria, microalgae) isolated from Mogan Lake was used for the removal of cadmium ions from aqueous solutions as its dry biomass, alive and heat-inactivated immobilized form on Ca-alginate. Particularly, the effect of physicochemical parameters like pH, initial concentration and contact time were investigated. The sorption of Cd(II) ions on the sorbent used was examined for the cadmium concentrations within the range of 25–250 mg/L. The biosorption of Cd(II) increased as the initial concentration of Cd(II) ions increased in the medium up to 100 mg/L. Maximum biosorption capacities for plain alginate beads, dry biomass, immobilized live Oscillatoria sp. H1 and immobilized heat-inactivated Oscillatoria sp. H1 were 21.2, 30.1, 32.2 and 27.5 mg/g, respectively. Biosorption equilibrium was established in about 1 h for the biosorption processes. The biosorption was well described by Langmuir and Freundlich adsorption isotherms. Maximum adsorption was observed at pH 6.0. The alginate–algae beads could be regenerated using 50 mL of 0.1 mol/L HCl solution with about 85% recovery.

Introduction

Heavy metal pollution of waters is a common environmental problem due to industrial processes which result in the release of heavy metals into natural water. Toxic metal ions such as Cd(II) can eventually reach the top of food chain and thus, become a risk factor for people’s health. Most of the heavy metal salts are soluble in water and form aqueous solutions and consequently cannot be separated by ordinary physical separation methods (Hussein et al., 2004). Conventional techniques for removing dissolved heavy metals include precipitation (Berbenni et al., 2000), adsorption (Nadeem et al., 2006), ion-exchange (Gode and Pehlivan, 2007). In recent years, alternative methods for metal removal and recovery based on biological materials have been considered. Biosorption and/or bioaccumulation have emerged as a cost-effective and efficient alternative method. Biosorption means the passive process for adsorbing the metal ions by metabolically inactive biomass, which is dependent on the affinity between the metallic species or its ionic forms and the binding sites on the molecular structure of the cellular wall (Manriquez et al., 1997, Pardo et al., 2003). Bioaccumulation is the term usually employed to describe the active sequestering of metal ions by metabolically active biomass (Hussein et al., 2004).

Microorganisms, including algae, bacteria, yeast, fungi, plant leaves and root tissues can be used as biosorbents for the removal of heavy metals (Pavasant et al., 2006, Bhanoori and Venkateswerlu, 2000, Hussein et al., 2004, Arıca et al., 2004, Ergene et al., 2006, Tüzün et al., 2005, Kaçar et al., 2002, Yang and Volesky, 1999, Chojnacka et al., 2005). Different species often had different sorption characteristics. There are evidences that some phenomena for metal binding, such as adsorption, ion exchange, chelating, precipitation and crystallization take place in cellular membrane of microorganisms (Pardo et al., 2003). The external factors such as pH, temperature, concentration of metal ion, contact time always affect the sorption of metal ions.

Cyanobacteria are the largest and most diverse group of photosynthetic prokaryotes whose habitats vary from fresh and marine water to terrestrial environments. The microorganism selected for this study was a filamentous cyanobacterium, Oscillatoria sp. H1. It is known that the filamentous cyanobacterium has a wide polysaccharide capsule surrounding its entire filament. Some cyanobacterial species such as Oscillatoria, Spirulina and Gleocapsa synthesize extracellular organic material such as siderophores with metal complexing properties. Aside from metal complexation with functional groups and proteins on algal surfaces, significant concentrations of metal cations are able to pass through the plasma membrane into the cell interior. In cyanobacteria, it was demonstrated that heavy metals are accumulated in intracellular storage compartments, called polyphosphate bodies, where metals accumulate, protect algal cells from toxicity (Kelly, 1988).

In industrial or technical operations, immobilized microbial cell systems could also provide additional advantages over freely suspended cells. These advantages include ease of regeneration and reuse of the biomass, easier solid–liquid separation and minimal clogging in continuous flow systems (Özdemir et al., 2005). Natural and synthetic sorbents such as alginate (Arıca et al., 2004), chitosan (Qi et al., 2006), cellulose (Sakurai et al., 2000), amberlite XAD resins (Baytak and Türker, 2005), sepiolite (Tunçeli et al., 2001) and silica gel (Godlewska-Zylkiewichz, 2003) have been mostly used as support material for the immobilization of microbial cells.

Alginate is a water-soluble natural polymer, which can be converted into hydrogels via crosslinking with divalent calcium ions. It was preferred over other materials as a support material due to such advantages as biodegradability and hydrophilicity, the presence of carboxylic groups. It was reported that the scanning electron micrographs of Synechocystis aquatilis immobilized on Ca-alginate beads were showed the uniform distribution of S. aquatilis in alginate structure and did not indicate any change in the morphology of S. aquatilis by immobilization (Ergene et al., 2006). This uniform distribution is an important criterion for the proper biosorption of heavy metal ions over the whole surface area of the algal immobilized beads.

In this study, Oscillatoria sp. H1, a cyanobacterium, was used as dead cell (dry biomass), immobilized live cell and immobilized heat-inactivated cell in order to remove cadmium(II) ion from aqueous solution. The purpose of the heat-treatment is to improve the surface characteristics of the fungal biomass in relation to their adsorbing mechanisms. It was then assumed that the pretreatment may lead to an increase of the charge on the cell surface or open the available sites for the adsorption and enhance ion-exchange (Bayramoğlu and Arıca, 2007). Thermal inactivation of microorganisms is associated with irreversible denaturation of membranes, ribosomes, and nucleic acids. However, the patterns of macromolecular changes that induce the cell death of microorganisms during heat treatment are still not clearly known (Lee and Kaletunç, 2002). Calcium alginate beads were used as a support material for immobilization. Comparative results have been obtained for dry biomass, immobilized live cell, immobilized inactivated cell and calcium alginate alone. The effect of immobilization and inactivation of the cyanobacterium has been evaluated. In this work, Oscillatoria sp. H1 was first used for heavy metal removal as a biosorbent. Oscillatoria sp. H1 has showed promising characteristics and it is not a hazardous microorganism for human (no toxicity). Toxins are produced by some strains of Oscillatoria sp. H1 (e.g. O. agardhii, O. erythraea) (Katırcıoğlu et al., 2004).

The effect of pH, initial concentration of cadmium, biosorbent dose and contact time on the biosorption were investigated. The effectiveness of desorbing agent (HCl) in stripping adsorbed metal ions from immobilized biomass was also investigated.

Section snippets

Apparatus

A Philips PU 9285 model flame atomic absorption spectrometer equipped with deuterium lamp background correction, hollow cathode lamp (HCL) and air acetylene burner was used for the determination of cadmium. Absorption measurements were performed under the following conditions: wavelengths, 228.8 nm; fuel flow rate, 1.1 L min−1; HCL lamp current, 9.0 mA; bandpass, 0.5 nm and integration time, 4 s. All pH measurements were performed with a JENWAY 3010 model digital pH meter.

Reagents

All chemicals were of

Effect of pH on Cd(II) biosorption

Metal ion biosorption onto biosorbents from aqueous solutions is depend on the pH of solution as it affects biosorbent surface charge, degree of ionization, and the species of biosorbents. The pH of the solution influence both metal binding sites on the cell surface and the chemistry of metal in solution. In order to demonstrate the effect of pH on biosorption, uptake of cadmium ion (100 mg/L) on the biosorbents as a function of pH was studied in the pH ranges of 2.0 to 8.0 adjusting by a

Conclusion

In this study, Cd(II) adsorption properties of dry biomass, plain alginate, immobilized live and heat inactivated Oscillatoria sp. H1 (cyanobacteria, microalgae) were studied. The immobilized live Oscillatoria sp. H1 showed a higher biosorption capacity than the dry biomass and heat-inactivated Oscillatoria sp. H1. Biosorption of Cd(II) took place very fast during the initial stage of contact. Biosorption capacities for Cd(II) were found to be strongly dependent on the pH of the solution and

Acknowledgements

The authors are grateful to Gazi University Research Fund for support of this work.

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