Bacterial Adhesion to Metal Oxide-Coated Surfaces in the Presence of Silicic Acid

Abstract

This study investigated the effect of silicic acid to the adhesion of Bacillus subtilis to metal oxide-coated surfaces. The first sets of column experiments were conducted under various concentrations of silicic acid. The second and third experiments were performed under various concentrations of sulfate and nitrate to compare the results from silicic acid. Bacterial breakthrough curves were obtained by monitoring effluent, and mass recoveries were quantified from these curves. The results show that, at silicic acid concentrations between 0 and 0.2 mM, bacteria were negatively charged, while the charges of metal oxides were changed from positive to negative. Bacterial adhesion to metal oxide-coated surfaces decreased sharply with increasing silicic acid concentration (bacterial mass recovery increased from 11.5 to 82.2%), as a result of the hindrance effect of silicic acid adsorbed onto metal oxide-coated surfaces. Between 0.2 and 10 mM, both bacteria and metal oxides were negatively charged. Bacterial adhesion remained constant (mass recovery were 80.5 to 82.2%), despite the increasing silicic acid concentration, possibly as a result of the hindrance effect of polymerized silicic acid. That is, the bacterial approach to the metal oxide-coated surfaces could be disturbed through steric hindrance of polymerized silicic acid, which compensates the potential enhancement effect from the electrical double layer compression. The results also illustrate that the effect of silicic acid on bacterial adhesion was greater than those of sulfate and nitrate. This study demonstrates that silicic acid can play a significant role in bacterial interaction with metal oxide-coated surfaces.