ACCUMULATION OF LEAD BY ANABAENA-CYLINDRICA - MATHEMATICAL-MODELING AND AN ENERGY-DISPERSIVE X-RAY STUDY

The ability of microorganisms to selectively adsorb various heavy meta l ions has been recognized for over a decade. We have investigated the biosorption of lead by an active culture of the cyanobacterium Anabae na cylindrica. Energy dispersive X-ray microanalysis was used to evalu ate the different uptake mechanisms in the various subcellular regions . Three were identified: a very fast adsorption mechanism in the cell envelope; a time-dependent deposition reaction on the cell surface; an d an adsorption mechanism, also time dependent, on the polyphosphate b ody inside the cell. Atomic absorption spectrometry was then used to q uantify the changes with time of bulk fluid concentrations of lead sol utions exposed to cyanobacteria. A mass transfer kinetic model was dev eloped which quantitatively predicts the concentration of lead in cell s of Anabaena cylindrica as a function of spatial dimensions and time. The model predictions are consistent with a pattern, documented in li terature and confirmed by our own experimental evidence, of a very fas t uptake in the cell envelope and then a longer uptake period inside t he cell. Our experimental evidence also revealed a time-dependent upta ke mechanism on the surface of the cells, which is included in the mod el. (C) 1997 John Wiley & Sons, Inc.