Comparative study of biosorption of Zn 2+ by Pseudomonas aeruginosa and Bacillus cereus

Abstract

Pseudomonas aeruginosa ASU 6a (Gram-negative) and Bacillus cereus AUMC B52 (Gram-positive) were used as an inexpensive and efficient biosorbent for Zn (II) removal from aqueous solutions. The effects of various physicochemical factors on Zn (II) biosorption such as pH – 1.0–7.0, initial metal concentration – 0.0–200 mg/L, and contact time – 0–60.0 min were studied. The optimum pH for Zn (II) removal was 6.0, while the optimal contact time was 30 min at 30 °C by the two bacterial species. The nature of the biosorbents and metal ion interactions were evaluated by Fourier transform infrared (FTIR) spectroscopy. FTIR analysis of bacterial biomass revealed the presence of amino, carboxyl, hydroxyl, and carbonyl groups, which are likely responsible for the biosorption of Zn (II). The Gram-negative bacterium showed more zinc biosorption compared to the Gram-positive bacterium. The maximum adsorption capacities by P. aeruginosa ASU 6a and B. cereus AUMC B52 calculated from Langmuir adsorption isotherms were 83.3 and 66.6 mg/g, respectively. The adsorption isotherms fitted well with both the Langmuir and Freundlich isotherm models with high values of correlation coefficient ( r 2 > 0.97). The biosorption kinetic data were properly fitted well with the pseudo-second-order kinetic model.