Fig. 3From: Modeling of methane formation in gravity sewer system: the impact of microorganism and hydraulic conditionVariation of biomass density at different wall-shear stresses; COD = 400 mg/L (F means wall-shear stress, Pa). At three wall-shear stresses of 0.8, 1.29 and 2.0 Pa, the average biofilm densities were 51 ± 3, 62 ± 5 and 80 ± 5 kg/m3, respectively, indicating that the average biofilm densities increased with the increase of wall-shear stressBack to article page