Effect of Shear Stress on Biofilm Morphological Characteristics and the Secretion of Extracellular Polymeric Substances

The effect of shear stress on the EPS secretion was investigated in a suspended carrier biofilm reactor. A sudden increase of shear stress on the biofilm enhanced the EPS- polysaccharides secretion after an acclimation period. However, as the biofilm´s structure reestablished and reached a steady state again, the EPS-polysaccharides secretion dropped down and stayed at a value which approximated to the volume before the change occurred. It makes microorganism taking longer to adapt higher shear stress. The increase in shear stress has little effect on the EPS-protein secretion. A higher shear stress caused the biofilm to lose its surface roughness but become flatter. Due to continuous change in the internal pore structures and bacteria´s self-aggregating, the biofilm gets more compact and dense with an increasing shear stress. When the liquid velocity was increased from 0.032 m/s to 0.056 m/s, then to 0.089 m/s, it was also observed that more erosion of the biofilm occurred.