KINETICS OF BIOSORPTION OF THREE HEAVY METALS BY FIVE SELECTED MICROORGANISMS

In the recent time, the use of low cost biosorbents like bacteria, fungi, algae and some agricultural by-products have been investigated for their biosorption capacities. In this work, the biosorptions of three heavy metals (zinc, copper and manganese) from aqueous wastewater solution by five micro-organisms (Bacillus circulans, Pseudomonas aeruginosa, Staphylococcus xylosus, Streptomyces rimosus and Saccharomyces sp.(Yeast) were investigated using a combined flow and batch process. The biosorbents were air/sundried without subjecting them to oven heat. Factors such as solution pH, initial metal ion concentration of heavy metals, mass of biosorbent and contact time were investigated. The removal efficiencies of the individual microbes were also calculated. The maximum metal uptakes for the biosorption of heavy metals occurred at pH between 5.5 - 6.5. The biosorption of zinc ion by Staphylococcus xylosus yielded the highest removal efficiency of 94%. Also, the biosorption of Copper and Managense ions by Bacillus circulans produced removal efficiencies of 97% and 90% respectively. The biosorption characteristics of the heavy metal ions using five selected microorganisms were investigated. Five existing kinetic equations namely: First order kinetic equation, second order kinetic equation, pseudo first-order kinetic equation, pseudo second-order kinetic equation, Elovich Kinetic Equation, Webber-Morris Kinetic Equation and two proposed kinetic equations were used to evaluate the kinetic properties of biosorption of the heavy metals. This was to know which of the kinetic equation could best describe the mechanism(s) of biosorption of each of the above three heavy metals by the individual microorganisms. Two parameters namely; linear regression coefficient of correlation (R2) and average relative error (ARE%) were used to study the effectiveness of each of the kinetic models. Highest value of R2 and least value of ARE% were established. In terms of highest values of R2, first proposed kinetic equation accounted for 46.7%, Pseudo second-order kinetics 40% while Elovich, Webber-Morris and second proposed kinetic equations accounted for 6.7% respectively of the results for biosorption of the three heavy metals by five selected micro-organisms. But comparison based on least values of ARE%, first proposed kinetic equation accounted for 93.3% while Pseudo second-order kinetic equation accounted for 6.7% of the results for biosorption of the three heavy metals by the five microbes. From the results, it is obvious that in terms of concentration, first proposed kinetic model should be adopted and in terms of biosorption capacity pseudo second-order model should be adopted for biosorption of heavy metals with infinite contact time. For the two biosorption isotherms, the range of value of linear regression coefficient of correlation (R2) produces by Langmuir isotherm are: zinc (0.8247 – 0.9986), Copper (0.6521 – 0.9902), Manganese (0.6803- 0.9880) while those of Freudlinch isotherm are: Zinc (0.9040 – 0.9999), Copper (0.7233 – 0.9832) and Manganese (0.7891 – 0.9753). The results of completely mixed flow equation show that biosorption rates are higher at the inception than towards the equilibrium.