Cadmium biosorption by cells of Spirulina platensis TISTR 8217 immobilized in alginate and silica gel
Introduction
The presence of heavy metals in the aquatic environment is a source of great environmental concern. Conventional techniques, such as chemical precipitation, ion exchange, activated carbon adsorption and membrane separation processes have limitations for the removal of heavy metals from wastewater. They become inefficient and expensive especially when the heavy metal concentration is less than 100 ppm Leusch et al., 1995, Yan and Viraraghavan, 2001. The ability of microorganisms to accumulate metal ions from aqueous solutions has been widely reported. Ting and Sun, 2000, Rangsayatorn et al., 2002, Tangaromsuk et al., 2002. It is a potential alternative to conventional processes for the removal of metals. Some researchers have found that stripping metals out of the biosorbents was difficult (Macaskie et al., 1997). However, Gaedea-Torresday et al. (2002) and Manju et al. (2002) have shown that desorption and regeneration of biosorbent can be easily done. The low strength and small particle size make it difficult to use in column application as well (Yan and Viraraghavan, 2001). Cell immobilization, which is applied to various biotechnological processes, is one approach that can avoid the biomass–liquid separation requirement. It can prevent the independent movement of cells during the aqueous phase of the system. Cell immobilization is a general term that describes many different forms of cell attachment or entrapment (Lopez et al., 1997). Various techniques are used for cell or biomass immobilization, such as flocculation, adsorption on surfaces, covalent bonding to carriers, cross-linking of cells, encapsulation in a polymer gel, and entrapment in a polymeric matrix. The physical entrapment of organisms inside a polymeric matrix, generally described as a gel, is one of the most widely used techniques for immobilization because a polymeric matrices can be made as beads with optimize mechanical strength, rigidity, and porosity characteristics Lu and Wilkins, 1995, Annadurai et al., 2000. Many diverse gel matrices have been proposed as possible carriers. Either natural biopolymers (polysaccharides, alginate, carrageenan, agar) or synthetic polymer (polyacrylates, polyurethanes, polyethers) can be used as gel-forming agents (Lozinsky and Plieva, 1998).
Alginate gel and silica gel are two commonly used entrapment matrices. Alginate is a heteropolymer of l-guluronic acid and d-monouronic acid. It is extracted from several species of marine algae and, after processing, is available as water-soluble sodium salts (Tampion, 1987). When the monovalent counter ion of sodium is replaced by divalent calcium, ionic cross-linking among carboxylic acid groups occurs and gives a gelatinous substance, calcium alginate. As a result of cross-linking, a polymeric network of polysaccharide molecules is formed in which about 60% of water is entrapped in gel (Phillips and Poon, 1998). Another inorganic synthetic polymeric matrix often used to entrap cells is porous silica gel. The use of silica gel cell for entrapment is called the sol–gel technique (Weller, 2000). The silica gel is generated by decreasing the pH of alkali silicate solution to less than 10. The solubility of silica is then reduced to form the gel. As the silica begins to gel, cells in silica are trapped in a porous gel, which is a three-dimensional SiO2 network (Chaiko et al., 1998).
The kinetics of metal uptake, assumed to be a physical adsorption to the cell surface, is very rapid and occurs shortly after the biosorbents contact the metal ions in solution. Kinetic studies of sorption are significant since the data can be used: (1) for determining the time required to reach equilibrium, and (2) to evaluate the maximum adsorption capacity (Singh et al., 2001). The metal uptake (q), for the construction of sorption isotherms, is determined as follows:where Ci and Cf are the initial and final metal concentrations (mg/l), respectively; V is the volume of sample solution (l); and M is the dry weight of added biomass (g). Traditionally, the Langmuir model has been used to evaluate maximum metal uptake. It is based on the basic assumptions that: (1) metal ions are chemically adsorbed at a fixed number of sites, (2) each site can hold one sorbed ion, (3) all sites are energetically equivalent, and (4) there is no interaction between ions adsorbed on neighboring sites (Inthorn et al., 1996). The Langmuir equation has the following formwhere b is a constant related to the energy of adsorption/desorption and qmax is the maximum uptake.
In this study, immobilized cyanobacterial cells, Spirulina platensis, were entrapped in two kinds of gel, alginate gel and silica gel. The cadmium adsorption capacity and reusability of the biosorbents were investigated.
Section snippets
Culture of cynobacteria
The cyanobacteria, S. platensis TISTR 8217, were obtained from the Thailand Institute of Scientific and Technology Research (TISTR), Bangkok, Thailand. S. platensis was inoculated onto Zarrouk medium (Becker and Venkataraman, 1984) and incubated under the continuous illumination of a cool white fluorescent lamp. Cell growth was determined by measuring the optical density of S. platensis at 560 nm. After 12 days, the culture was in the linear growth phase. The cells were collected and washed
Biosorption rates
Fig. 1 shows the changes in cadmium adsorbed onto beads with time. Rapid biosorption rates were observed at the beginning (first 5 min), which then reached the equilibrium stage at about 45 min for both alginate and silica gels. At the equilibrium stage, the cadmium adsorption was higher than 95% for both immobilized cells on alginate and on silica gels. For the negative control, which was the gel bead alone with no biomass entrapped in it, cadmium was adsorbed by 5.75% and 7.88% for the silica
Conclusion
The removal of heavy metal ions from aquatic systems is carried out using classical adsorption techniques. S. platensis immobilized on alginate and silica gels were applied to remove cadmium from the solution. The results of this study showed a high cadmium sorption capacity of immobilized cyanobacterial cells. They could be repeatedly used in multiple adsorption–desorption cycles. Metal sorption decreased after the first desorption, but sorption capacity was still high. Temperature did not
Acknowledgements
This work was supported by the Royal Golden Jubilee PhD program of the Thailand Research Fund (grant no. 00093/2541) and the Development and Promotion of Science and Technology Talents Project (DPST).
References (31)
- et al.
Production and utilization of the blue-green alga Spirulina in India
Biomass
(1984) - et al.
Synthesis and analytical properties of a chelating resin functionalised with bis-(N,N′-salicylidene)1,3-propanediamine ligands
Talanta
(1996) - et al.
Immobilized marine algal biomass for multiple cycles of copper adsorption and desorption
Sep. Purif. Technol.
(2000) - et al.
Removal of cadmium from aqueous solution by the filamentous cyanobacterium Tolypothrix tenuis
J. Ferment. Bioeng.
(1996) - et al.
The interphase technique—a simple method of cell immobilization in gel-beads
J. Microbiol. Method
(1997) - et al.
Poly(vinyl alcohol) cryogels employed as matrices for cell immobilization. 3. Overview of recent research and developments
Enzyme Microb. Technol.
(1998) - et al.
An investigation into the sorption of heavy metals from wastewaters by polyacylamide-grafted iron(III) oxide
J. Hazard. Mater.
(2002) - et al.
Cross-frontal exchange of Antarctic intermediate water and Antarctic bottom water in the Crozet basin
Deep-Sea Res., Part 2, Top. Stud. Oceanogr.
(1997) - et al.
Phytoremediation potential of Spirulina (Arthrospira) platensis: biosorption and toxicity studies of cadmium
Environ. Pollut.
(2002) - et al.
Trace metal analysis: selective sample (copper II) enrichment on an AlgaSORB column
Process Biochem.
(2000)
Ni(II) and Cr(VI) sorption kinetics by Microcystis in single and multimetallic system
Process Biochem.
Cadmium biosorption by Sphingomonas paucimobilis biomass
Biores. Technol.
Heavy metal removal in a biosorption column by immobilized M-rouxii biomass
Biores. Technol.
Adsorption of copper and chromium by Aspergillus carbonarius
Biotechnol. Prog.
Adsorption and bio-degradation of phenol by chitosan-immobilized Pseudomonas putida (NICM 2174)
Bioprocess Eng.
Cited by (178)
Microalgal-based macro-hollow loofah fiber bio-composite for methylene blue removal: A promising step for a green adsorbent
2023, International Journal of Biological MacromoleculesPhotobioreactor design and parameters essential for algal cultivation using industrial wastewater: A review
2023, Renewable and Sustainable Energy ReviewsFast-growing cyanobacteria bio-embedded into bacterial cellulose for toxic metal bioremediation
2022, Carbohydrate PolymersCyanobacterial biofilms: Formation, distribution, and applications
2022, Expanding Horizon of Cyanobacterial BiologyA review on advances and mechanism for the phycoremediation of cadmium contaminated wastewater
2021, Cleaner Engineering and Technology