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Parameters determining sorption processes for heavy metal recovery

Several different systems have been developed to use biomass for the removal and/or recovery of heavy metals from waste water streams after establishing the genetic, biochemical, cellular and microenvironmental parameters that influence bacterial sorption and bioprecipitation processes. No general model could be made but descriptive models specific for each strain and for each metal were developed.

Metal bioprecipitation is a process that is always preceded by an adsorption process. So it will first obey the model of adsorption and afterwards be followed by an active system that can be described by a stoichiometry where, as long as reacting components are available, the reaction proceeds in one direction taking the metal ion from the ionic solution state into a form that is no longer in solution. Thus, metals can be accumulated continuously against a concentration gradient.

So for the different systems model bacteria were used which focused on cellular surface adsorption extracellular polymer adsorption, nonselective adsorption, neutral charge adsorption, phosphatase mediated bioprecipitation, heavy metal resistance mediated bioprecipitation and bioprecipitation via reduction. It may also be clear that these mechanisms are not just single phenomena but do have some interactions in some bacteria.

The use of such bacterial metal adsorption or bioprecipitation systems for metal removal or metal recovery in industrial applications is determined by the metal binding capacity and the regeneration and restoration of biomass. As a conclusion it can be said that strains useful for application do need a high binding capacity or high precipitation capacity together with a good regeneration capacity. Therefore it is necessary to find not only good bacteria but also good regeneration systems or systems that make new biomass in order to keep these 2 requirements high.

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