Biosorption of Heavy Metals from Aqueous Solution using Bacillus Licheniformis

More documents

Recommendations

Info

Int. J. Pure Appl. Sci. Technol., 10(2) (2012), 12-19. 13 Introduction: Certain species of micro organisms have found to adsorb surprisingly large quantities of heavy metals. Many of these metals include those causing toxicity to humans and metals of commercial and economic importance. Removal of metals and their recovery is one of the major concerns in sewage and industrial effluent treatment, which is both in municipal and industrial interest. The heavy metals of widespread concern to human health are mercury, cadmium, lead, arsenic, chromium, copper, and zinc (Lazrova et al., 2005). Nriagu (1988) estimated that over one billion human beings are currently exposed to elevated concentrations of toxic metals and metalloids in the environment and several million people may be suffering from subclinical metal poisoning. Adverse effect of heavy metals include i) suppression of the immune system ii) carcinogenicity (Peakall, 1992), iii) neurotoxicity, mainly in children (Cohen, 2005) iv) inhibition of the activity of some critical enzymes related to synthesis of vital bio-molecules v) accumulation in the body of different organisms causing biomagnification (Paknikar et al., 2003). Physico-chemical methods, such as chemical precipitation, oxidation or reduction, electrochemical treatment, evaporative recovery, filtration, ion exchange and membrane technologies are widely used to remove heavy metal ions from industrial wastewater. However, application of these treatment processes has been found to be sometimes restricted, because of investment, operational costs and the potential generation of secondary pollution. These processes may be ineffective or expensive, especially when the heavy metal ion concentrations in solutions are 1-100 mg L -1 (Volesky, 1990a, b). It was only in the 1990s that a new scientific area developed that could help to recover heavy metals using biological means i.e. 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 (Vieira and Volesky 2000). The technique of biosorption utilizes the characteristics of microoganisms to adsorb metals in a commercial manner. Microorganisms uptake metal, either actively (bioaccumulation) and/or passively (biosorption) (Fourest and Roux, 1992). This is due to affinity of bacterial surfaces for heavy metals leading to their adsorption and precipitation. The biosorption is passive non-metabolic process of binding various chemicals on biomass (Volesky, 1990a). Most studies of biosorption for metal removal deal with the use of either laboratory-grown microorganisms or biomass generated by the pharmacology and food processing industries or wastewater treatment units (Tsezos and Volesky, 1981; Hussein et al. 2004). Bacillus licheniformis (B.licheniformis) is frequently used in waste water treatment in combination with Bacillus subtilis (Hiatt 2000, Kalia et al. 1994) due to the production of extracellular enzymes, mainly protease and lipase. The extraordinary characters of organism which support its application in sewage treatment are its diverse habitat, ease of cultivation, non pathogenic nature to humans, spore forming ability and its tolerance to environmental stress, starvation etc. There are many reports describing metal binding sites of B. licheniformis. Other than peptidoglycan (basic component of cell wall), B. licheniformis cell wall has high proportion of teichoic and teichouronic acid, both of which are responsible for about 60% of metal binding (Beveridge, 1982). These characteristics of B.licheniformis prompted us to study efficacy of its living biomass in heavy metal removal. This work mainly deals with biosorption of hexavalent chromium ion, cupric ion and ferric ion by whole cell broth of B.licheniformis (NCIM 2471). Effects of change in pH and incubation temperature on metal removal were also studied. Our studies also aimed at determination of heavy metal tolerance of the organism using the metal ions individually and in combination. Materials and Methods: All the chemicals were procured from Merck, India and were of A.R grade whereas all media components were from Hi Media, India. B. licheniformis (NCIM 2471) was obtained from National Collection of Industrial Microorganisms, National Chemical Laboratory, Pune, India. The strain was maintained by subculturing on nutrient agar. The culture was stored at 4° C between transfers and subcultured before experimental use.
Int. J. Pure Appl. Sci. Technol., 10(2) (2012), 12-19. 14 Metal Solutions: Experimental metals used in the study were chromium (VI), copper (II) and iron (III) in the form of their respective metal solutions. A synthetic multi-element standard solution of liquid media (1% tryptone, 0.5% yeast extract, 0.5% NaCl) containing 150 mg L -1 of each Cr, Cu and Fe ions was prepared from their respective stock solutions (1000 mg L -1 ). Chemicals used for preparing these stock solutions where potassium dichromate, copper sulphate and ferric chloride. Stock solutions of these metals were prepared using deionized water and autoclaved separately. Prior to addition of stock solution of metals the liquid media were autoclaved at 121°C for 20 min. All the additions were performed aseptically. Effect of pH on Biosorption: The experiments were carried out in the batch mode for the measurement of biosorption capabilities. Medium containing synthetic multi-element solution (15 mg % of each metal) in 500 ml Erlenmeyer flask was used. Before the addition of the biosorbant inoculum to the solution the samples were adjusted to different pH values viz. pH- 2.5, 3, 3.5, 4, 4.5. The pH of solution was adjusted with 1 M HCl and 1 M NaOH solutions. Samples were inoculated with 10% overnight grown culture of B.licheniformis and then incubated at 120 rpm for 48 hrs. The inoculated samples were then incubated at 28°C for 48 hrs. After the incubation period the cells were harvested by centrifugation for 30 min at 5000 rpm. Total metal concentration biosorbed by B. licheniformis was analysed using Inductive Coupled Plasma-Atomic Emission Spectrophotometer (ICP-AES) (JY-24, Jobin yvon, France). Effect of Incubation Temperature on Biosorption: A set of three samples was prepared as described above and pH was adjusted to 3.5 for all three samples. After inoculation, samples were incubated at temperatures i.e. 20°C, 28°C, 37°C respectively and incubated at 120 rpm for 48 hrs. Total metal concentration biosorbed by B. licheniformis was analyzed using ICP-AES as described above. Determination of Metal Tolerance: Colorimetric method was used to determine maximum tolerable concentration (MTC) of B. licheniformis for hexavalent chromium ion, cupric ion and ferric ion. Four sets of experiments were prepared using liquid media as mentioned above. First three sets had varying concentrations (200 mg L -1 to 1500 mg L -1 ) each of chromium, cupric and ferric ion respectively. In the fourth set, the samples contained all metal ions in the range of 200 mg L -1 to 1500 mg L -1 . Thus total metal concentration varied from 600 mg L -1 to 4500 mg L -1 in the samples in fourth set of experiments. The pH was maintained at 3.5 for all four sets. 10 % overnight grown culture of B. licheniformis was inoculated in these samples and incubated at 28°C, 120 rpm for 48 hrs. Growth was determined by measuring absorbance at 540 nm. Samples showing zero absorbance were further confirmed for growth by examining total viable count (TVC). Maximum tolerable concentration (MTC) of heavy metal was designated as the highest concentration of heavy metal that allowed growth after 2 days (Schmidt and Schlegal, 1994). All the experiments were carried out in triplicates and the results indicate the mean values. Results and Discussion: Biosorption Studies: The living biomass of B. licheniformis (NCIM 2471) was used for biosorption studies of Cr (VI), Cu (II) and Fe (III) ions. Effect of pH and incubation temperature was studied on removal efficiency of the organism.
Page 1: Int. J. Pure Appl. Sci. Technol., 1
Page 5 and 6: Int. J. Pure Appl. Sci. Technol., 1
Page 7 and 8: Int. J. Pure Appl. Sci. Technol., 1

Biosorption of Heavy Metals from Aqueous Solution using Bacillus Licheniformis

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?