Biosorption potential of Bacillus anthracis PM21 for the sequestration of cadmium, chromium, and nickel from contaminated water

Heavy metal pollution is a serious threat to the environment. The current study aims to assess the role of Bacillus anthracis PM21 for the adsorption of cadmium Cd(II), chromium Cr(VI), and nickel Ni(II) from contaminated water. Possible mechanisms and bacterial surface changes during the adsorption process were evaluated at constant temperature (35 +/- 2 degrees C). The maximum biosorption (q) values 22, 57.04, and 5 mg/g for Cd, Cr, and Ni were observed at pH 8, 6, and 4, respectively. The optimum contact time for biosorption was 60 min at 50 mg L-1 concentration of heavy metals. Isotherm models were used to simulate the metals biosorption onto Bacillus anthracis PM21 surface at equilibrium. Langmuir's model gave the best fit with R-2 values for Cd = 0.997, Cr = 0.996, and Ni = 0.976. The adsorption kinetics followed the pseudo-second-order kinetic model. The Fourier-transform infrared spectroscopy analysis showed that different surface ligands: OH, C-O-C, C=O, S=O, N-O, CH2, and C-H, could be involved in the biosorption of metals on to Bacillus anthracis PM21. The scanning electron microscope analysis showed that bacterial cells exposed to Cd, Cr, and Ni were rough and exhibited more cell size relative to the unexposed cells. There was adhesion of polymeric substances on the bacterial cell wall. Results revealed a variation in cell size, but cells maintained their shape. It is concluded that the B. anthracis PM21 is a promising biosorbent for the elimination of Cd(II), Cr(VI), and Ni(II) from aqueous solutions.