Biosorption of heavy metal ions by Citrobacter freundii Bryan S Wang, Pek Jie Hui, Quah Jun Zhi James Hwa Chong Institu

1. Biosorption of heavy metal ions by Citrobacter freundii Bryan S Wang, Pek Jie Hui, Quah Jun Zhi James Hwa Chong Institution (High School Section) • Introduction • Heavy metal ions are non-degradable. Thus they pose health risks to organisms including humans. • Some plants are known to hyperaccumulate heavy metal ions. However, they are slow-growing plants with low biomass. • Microorganisms such as Bacillus sp. and Pseudomonas sp. have been shown to adsorb these ions. • The rationale of this study is to identify other types of bacteria that adsorb ions. Abstract Heavy metal pollution in the environment is mainly caused by illegal disposal of industrial wastes. These ions include lead, cadmium, zinc, mercury, manganese, copper (II) and iron (III). This project explores the effectiveness of using the Gram-negative bacterium, Citrobacterfreundii, in biosorption of these ions. C. freundii was most efficient at adsorbing copper (II) and iron (III) ions, at 26.8% and 28.9%, respectively, probably due to the least inhibition of its growth in the presence of these two ions. Copper (II) ions were adsorbed with the highest efficiency at pH 5.65. A significant degree of adsorption of copper (II) ions was also observed with cells of C. freundii immobilized in sodium alginate. Variables • Objectives • To investigate the type of heavy metal ions most effectively adsorbed by C. freundii with minimal decrease in its growth rate • To investigate the optimal pH at which C. freundii adsorbs heavy metal ions • To investigate the effect of immobilization of C. freundii cells on biosorption • Hypotheses • C. freundii can efficiently adsorb copper (II), iron (III), zinc and manganese ions, resulting in a decrease in their concentrations in the culture supernatant • Efficiency of adsorption of ions is affected by pH of growth medium • Immobilized C. freundii cells are able to adsorb ions Adsorption of heavy metal ions Growth of C. freundii Determination if growth of C. freundii is affected by metal ions C. freundii grown in LB broth with metal ion (test) C. freundii cells wereprecultured in 25 ml LB broth at 30C for 24 h with shaking Cells were harvested by centrifugation at 8000 rpm for 10 min C. freundii grown in LB broth (control) C. freundii grown in LB broth containing each heavy metal ion (test) 1 ml of preculture transferred LB containing metal ion without C. freundii (control) Supernatant was collected 9 ml LB broth containing each heavy metal ion (Cu2+, Fe3+, Zn2+, Mn2+) 9 ml LB broth (basis of comparison to find out if metal ions affected growth) Absorbance at 600 nm was taken to determine cell density Concentration of ions was determined with ion test kits and colorimeter Incubated at 30C for 48 h with shaking Test for effect of pH on adsorption Test for effect of immobilized cells on adsorption Test for adsorption of heavy metal ions Set-ups Set-ups Immobilization of C. freundii cells in sodium alginate LB + copper (II) ions, in 5 different pH values To find out if pH of broth results in decrease in ion concentration in the absence of C. freundii Control without C. freundii LB + heavy metal ions (Cu2+, Fe3+, Zn2+, Mn2+) Basis of comparison to find out if concentration of ions decreases in the absence of C. freundii Control without C. freundii • C. freundii suspension was concentrated and added to equal volume of sodium alginate • Sodium alginate was added dropwise to calcium chloride solution • 30 beads were used for each set-up Control with C. freundii Control with C. freundii LB only Basis of comparison to find out if ions affect growth of C. freundii LB only, in 5 different pH values To find out effect of different pH on growth of C. freundii LB + copper (II) ions, in 5 different pH values LB + heavy metal ions (Cu2+, Fe3+, Zn2+, Mn2+) Test with C. freundii Test with C. freundii Set-ups LB + copper (II) ions Basis of comparison to find out if concentration of ions decreases in the absence of C. freundiibeads Control without C. freundii beads LB + copper (II) ions Test with C. freundii beads • Applications • C. freundii is fast-growing, thus effective in biosorption • Immobilization of cell biomass ensures that C. freundii cells are not released directly into the ecosystem, thus maintaining balance in ecosystem • Further Work • Investigate minimal cell biomass of C. freundiifor adsorption • Test effectiveness of C. freundiiin adsorption of other ions such as lead • Test on ways of immbolisingC.freundii into real life polluted water sources (including the use of other encapsulating methods and by using dead C. freundii cells). • C. freundii was most efficient at adsorbing copper (II) and iron (III) ions, at 26.8% and 28.9%, respectively • This is probably due to least inhibition of growth in the presence of these two ions C. freundii was most efficient at adsorbing copper (II) ions at pH 5.65 and 7.65. • Bibliography • Alloway, B.J. (1995). Plant uptake of metals. Heavy Metals in Soils. (Ed. B. J. Alloway). pp. 20-28. England: Springer. • Alluri H.K., Ronda S.R., Settalluri V.S., Bondili J.S., Suryanarayana V., Venkateshwar P. (2007), Biosorption: An eco-friendly alternative for heavy metal removal. African Journal of Biotechnology,6(25), 5-12. • Duruibe, J.O., Ogwuegbu, M.O.C. and Egwurugwu, J.N. (2007) Heavy metal pollution and human biotoxic effects, International Journal of Physical Sciences, 2(5), 112-118. • Prasad, M.N.V. and Freitas H.M.O. (2003). Metal hyperaccumulation in plants – Biodiversity prospecting for phytoremediation technology, Electronic Journal of Biotechnology,6(3), 286-297.