Influence of temperature on cadmium removal by Sphaerotilus natans from acidic solutions

A culture of Sphaerotilus natans (NCIMB 11196) was used for cadmium removal from acidic solutions, simulating the composition of industrial wastewaters. Tests were carried out at temperatures increasing from 15 up to 40degreesC, to check the actual possibility of utilizing a biological system to remove this heavy metal from water as well as, to shed light on the phenomenon responsible for its uptake. The highest values of the specific growth rate of this microorganism (mu(max)=0.11 to 0.13 h(-1)) and cadmium removal rate (k(r)=0.15 h(-1)) were obtained within 25 to 30degreesC. Under these conditions, biomass was able to increase the pH of the medium from 4.0 up to 7.0 to 7.8. The data of mu(max) and k(r) collected at different temperatures were finally used. to estimate, according to Arrhenius, the thermodynamic parameters of cell growth and cadmium removal as well as of the related thermal inactivations. On the basis of these results, cadmium seemed to be removed by S. natans following a mechanism controlled by cell growth, implying the quick electrostatic attraction of ions to the negative charges present on the cell surface.