Biofilms consisting of a matrix of exopolysaccharide and microorganisms developed over granular activated carbon (GAC) enhance metal uptake from solution several times more than that achieved by GAC alone. By specifically employing GAC, there is also the opportunity of developing biofilm/GAC systems that can both entrap metals and also adsorb, and ultimately degrade, polluting organic residues such as pesticides. Targets for this type of process could be dump site leachates, mine tailings and other industrial wastes. The conditions under which the biofilm is developed, including pH and temperature have, therefore, been studied in terms of subsequent influence on metal bisorption.

Uptake capacity of many low boiling point volatile organic compounds (VOCs) by granular activated carbon (GAC) is reduced by the released heat of absorption. However, by heat-fixing over GAC a biofilm consisting of bacteria in exopolysaccharide there was a significant reduction in the exotherm in subsequent chloroform vapour adsorption. This reduction was apparently related to a marked increase in surface basicity, possibly due to functional groups, such as hydroxyl and amino, present in the biofilm. Furthermore, incorporation of biosorbed zinc prior to heat-fixation resulted in a significant increase in chloroform loading due, at least in part, to the reduced exotherm allowing greater time for zinc/VOC interaction.

Selected biofilms attached to granular activated carbon significantly enhance metal recovery through biosorption. To describe uptake of five metals, the Freundlich isotherm model was found superior to the Langmuir. Calculated diffusion coefficients through the biofilm indicated a dependence between diffusivity and metal ion concentration.

A comprehensive biofilm of bacteria bound together in an excreted polysaccharide matrix and attached to granular activated carbon (GAC), is shown to enhance both rate and quantity of metal uptake from contaminated solutions. Electron micrographs illustrate an open film that provides a high surface area for biosorption of metal ions such as cadmium, copper, zinc and nickel. Studies have provided data on both equilibrium loadings (mg metal/g adsorbent) and adsorption rate coefficients. This data indicated the superior performance of the biofilm. This system, employing GAC as a biofilm support, has been demonstrated to both entrap metals and also adsorb other contaminants, including an organic residue (atrazine).

The bacteriumEnterobacter aerogenes has been used to develop a biofilm over activated carbon for biosorption from various strength cadmium solutions (25–500ppm). High bacterial resistance to metal poisoning allowed biofilm regeneration to raise the net loading of cadmium over the carbon by repeated biosorption runs.