Adhesion kinetics of nitrifying bacteria on various thermoplastic supports

The adhesion kinetics of nitrifying bacteria on various thermoplastic supports (polyethylene, polypropylene, polystyrene) were investigated by static adhesion tests. A simple kinetic model was presented that described the initial accumulation process of nitrifying bacteria on the supports. This model was then employed to study the effects of various factors on the adhesion kinetics of nitrifying bacteria. The findings indicated that the maximum adhesion rate was attained at a suspended bacterial concentration of 30 mg mixed liquor suspended solids 1(-1), and then stabilized. This implied that the external transfer of the suspended nitrifying bacteria to the support surface was a rate-limiting factor for the initial adhesion process at low concentrations of the suspended bacteria. A typical inverse V-shaped pattern between the adhesion rate and the pH in the liquid phase was observed, and the maximum adhesion rate was reached at pH 4.8. It was found, however, that the adhesion rate was linearly related to the aqueous ionic strength in the range 0.02-0.2 M NaCl equivalent. The adhesion capacity of nitrifying bacteria on the thermoplastic supports was found to be independent of the physico-chemical factors mentioned. This study clearly showed that non-biological processes may play an important role in the initial events of nitrifying bacterial adhesion on thermoplastic supports.