A comparative study of the adsorption of humic acid, fulvic acid and phenol onto Bacillus subtilis and activated sludge

The specific adsorption values collected at optimum pH revealed that with the materials used in this work both B. subtilis and activated sludge follow the same adsorption trend: humic > fulvic > phenol. The lower adsorption of fulvic acid as compared with humic acid may be explained in terms of its lower hydrophobicity rather than its lower molecular size. On comparing the specific adsorption values of activated sludge versus B. subtilis, similar but lower figures were found for the three organic compounds studied. This similar behaviour suggests that both types of biomass base their adsorption capacity on the general characteristics of the bacterial cell wall, and the lower adsorption by the sludge would be due to a lower specific area due to clustering of the cells. This is remarkable, since sludge is a heterogeneous and cheap material in comparison with cultured bacterial cells.