Effects of operating conditions on the adhesive strength of Pseudomonas fluorescens biofilms in tubes

Understanding the mechanical properties of biofilms, especially the force required to disrupt them and remove them from substrata is very important to development of antibiofouling strategies. In this work, a novel micromanipulation technique with a specially designed T-shaped probe has been developed to serve as an experimental means to measure directly the adhesive strength of biofouling deposits on the surface of a glass test stud. The basic principle of this novel technique is to pull away a whole biofilm accumulated on the surface of a glass test stud with T-shaped probe, and to measure simultaneously the force imposed on the biofilm. The adhesive strength between the biofilms and the surface to which they are attached, is defined as the work per unit area required to remove the biofilms from the surface. The biofouling experiments were performed on an elaborate design of a simulated heat exchanger system. A monoculture of Pseudomonas fluorescens was chosen as the fouling microorganism for the laboratory studies. Results indicate that the adhesive strength of the biofilm was affected by the conditions of operation, such as biofilm age, nutrient concentration, suspended cell concentration, pH, surface roughness of the substratum and fluid velocity. As noted, the effect of fluid velocity on the biofilm adhesive strength seemed to overwhelm other factors. At the same operating conditions, the biofilm adhesive strength increased as the fluid velocity increased within the range of 0.6-1.6m/s. In addition, the flow-related biofilm structures were observed that biofilms generally grew as a more compact pattern at the higher fluid velocity. Apparently, the fluid velocity can affect the biofilm structure, which in turn determines the biofilm adhesive strength. The knowledge of the biofilm adhesive strength with associated influences of the operating conditions may be used to define better cleaning procedures.