3.3.1 Flow rate
Water flow can promote the migration of bacteria to surfaces[108]. Some studies have shown that increased shear force due to the fluid can increase the rate and number of bacteria adhering to the material. However, when the velocity of the fluid exceeds a critical value, the juice inhibits bacterial adhesion. It even separates bacteria that have already adhered to the aggregate, and the critical value is related to the material to which the bacteria adhere [109]. At low flow rates, the direction of movement of adherent bacteria is random and disordered. As the flow rate increases, the orientation of the bacteria becomes closer to the streamline and aligns with the flow direction[110].
Zhang [111] used microfluidics to construct a micron-scale device to simulate the effect of shear force on bacteria adhering to the inner walls of micron-scale channels at different flow rates (0.5 mL/h to 1700 mL/h). The experimental results showed that: (1) the number of bacteria adhering to the surface remained constant after the shear force was increased to 200 Pa (150 m/h). The bacteria did not fall off the surface even if the shear force was increased further. The strong adhesion of the remaining bacteria on the surface may be related to their extracellular proteins and polysaccharides. (2) The number of surface-adherent bacteria was related to the application path of the shear flow field, i.e., the number of surface-adherent bacteria under directly increasing shear stress was lower than the number of surface-adherent bacteria under the corresponding shear flow field with a gradient increase.