Biofilm formation under turbulent conditions: External mass transfer versus shear stress

Abstract

This work investigates the effect of flow rate variation on the development of Escherichia coli biofilms formed in a flow cell system under turbulent conditions. Two flow rates were tested corresponding to Reynolds numbers of 4350 and 6720. The higher flow rate favored planktonic growth whereas the lower flow rate enhanced biofilm formation. Despite this, similar glucose consumption values were obtained in the whole system for both flow rates. Estimation of the external mass transfer coefficients by empirical correlations indicated that as the flow rate increased 1.5 fold, the external mass transfer coefficient increased 1.4 fold. Estimation of the shear stress in the flow cell was done by computational fluid dynamics and simulations indicated that the average shear stress increased 2.0 fold at the higher flow rate. Our results indicate that although external mass transfer is favored by an increase in flow velocity, the increase in shear stress had a negative impact on biofilm development. These results may have implications on biofouling control procedures where the use of high pressure/shear stress regimes and the use of cleaning/disinfection agents, that have to be transported from the bulk solution to the liquidbiofilm interface, is common practice.