Activated carbon surface modifications by adsorption of bacteria and their effect on aqueous lead adsorption

The adsorption of Escherichia coli on different activated carbons has been studied. The activated carbon samples used have been characterized, determining their surface area, pore size distribution, elemental analysis, mineral matter analysis and pH of the point of zero charge. The adsorption capacity of these carbons increased with their hydrophobicity and macropore volume. The number of bacteria adsorbed on the demineralized activated carbon in a solution of pH value equal to the iso-electric point of the carbon was negligible. However, in the presence of cations the proportions of bacterial cells adsorbed were 87.8% (Fe 3‡), 54.7% (Ca 2‡) and 24.8% (Mg 2‡) respectively. This increase in adsorption capacity in the presence of electrolytes has been explained on the basis of both the reduction in electrostatic free energy and the increase in cell surface hydrophobicity due to the metal bound by some compounds of the cell membrane. When the solution pH was intermediate between the pH values of the point of zero charge of the carbon and bacteria the number of bacteria adsorbed increased due to the attractive interactions between the carbon and bacteria. The adsorption of bacteria on activated carbons decreased the porosity and increased the negative charge density of the latter. Depending on the experimental conditions used, the presence of bacteria can enhance the capacity of activated carbons to adsorb lead. 1 INTRODUCTION Granular activated carbon (GAC) ®lters are used as a ®nal polishing step in drinking water treatment to remove compounds that are not usually present in the water at high concentrations (algae toxins, pesticides, taste, odours and industrial micropollutants). In addition, this treatment is recognized as an effective process for removing naturally occurring organic material formed by the breakdown of animal and vegetable matter in the environment. Nevertheless, this process can result in bacterial colonization of GAC,