Purpose
The purpose of this study is to obtain insights into how bacterial adhesion to soils affect the surface charges of soil Fe/Al hydroxides.
Materials and methods
Adhesion of Escherichia coli and Bacillus subtilis by amorphous Fe and Al hydroxides was investigated using a batch method. Zeta potential measurements and potentiometric titrations were used to study the effects of bacteria adhesion on the surface charges of Fe and Al hydroxides.
Results and discussion
The amorphous Al(OH)3 adhesion capacity of the two bacteria species was greater than that of amorphous Fe(OH)3 due to the much larger positive charge on amorphous Al(OH)3 compared to amorphous Fe(OH)3. The maximum Al(OH)3 adhesion capacities, obtained by fitting a Langmuir equation, were 2,689.6 and 2,358.7 g/kg for E. coli and B. subtilis, respectively, and the maximum Fe(OH)3 adhesion capacities of the two bacteria were 750.5 and 893.6 g/kg, respectively. Adhesion of both E. coli and B. subtilis to amorphous Fe and Al hydroxides decreased with increasing pH at pH < their points of zero charge (PZC), which was consistent with the change in interaction energy, as calculated by the classical DLVO theory, between the bacteria and the Fe/Al hydroxides. The electrostatic force plays an important role in bacterial adhesion by the Fe and Al hydroxides. The FTIR spectra revealed that chemical bond formation also contributed to the interactions between the bacteria and amorphous Fe and Al hydroxides. E. coli and B. subtilis adhesion decreased the positive charges and zeta potentials of the Fe and Al hydroxides, and shifted the PZCs of the Fe and Al hydroxides to lower pH. The larger number of negative charge on B. subtilis meant that it had a greater effect on the surface charge properties of the Fe and Al hydroxides compared to E. coli.
Conclusions
Electrostatic force plays an important role in E. coli and B. subtilis adhesion to amorphous Fe and Al hydroxides. Bacterial adhesion led to the decreases in positive charges and PZCs of the hydroxides.