Study of bacterial adhesion onto immobilized TiO2: Effect on the photocatalytic activity for disinfection applications

Abstract

A study has been carried out to determine the influence of bacterial adhesion onto immobilized TiO2 on the photocatalytic efficiency for bacteria inactivation. Two bacterial strains with differences in their membrane structure (Escherichia coli and Enterococcus faecalis) have been characterized in various suspensions for adhesion to the TiO2 catalyst and surface charge. Non-meaningful differences have been observed regarding the adhesion properties between both bacteria. In contrast, the configuration of the catalyst and the composition of the suspension impacted the extent of bacterial adhesion. The solution affected the adhesion between bacteria and catalyst due to its influence on electrostatic forces between them. Under electrostatically favourable conditions, hydrophobicity is the primary mechanism of adhesion. Under unfavourable conditions aquatic chemistry governs the bacterial adhesion process. Organic matter in combination with divalent ions leads to the highest level of adhesion. This may be due to the presence of Ca2+ which can bridge between bacteria and catalyst. Additionally, Ca2+ can also bridge with organic matter, which can act as source of nutrients for bacteria. Despite the solution ionic strength being low, divalent cations can contribute to the compression of the electric double layer, enhancing cell-catalyst interactions and subsequent adhesion. The bacterial adhesion observed in wastewaters might be responsible for the fact photocatalytic bacterial inactivation efficiency was not as low as expected since the main role of ions and organic matter is to act as scavengers of hydroxyl radicals.