Fig. 7
Microorganism amount vs wall-shear stress, COD = 400 mg/L. The amount of microorganism increased with the increase of wall-shear stress until the wall-shear stress reached 1.45 Pa. When wall-shear stress exceeded 1.45 Pa, although the biofilm density increased as well, the thickness of biofilm decreased at a greater degree, resulting the drop of the microorganism amount. When the wall-shear stress was 1.45 Pa, the average biofilm density was 74 ± 5 kg/m3, just 7.5% less than which obtained at wall-shear stress of 2.0 Pa, while the biofilm thickness was 2.4 ± 0.1 mm, 20.8% greater than which reached at wall-shear stress of 2.0 Pa. The R2 of Eq. (3) was 0.91, indicating that it is reasonable