Influence of Air Scouring and Residual Fouling on Cake Build-Up and Compression in Membrane Bioreactors

Compressible cake formation in membrane bioreactors, a key fouling mechanism in domestic wastewater reclamation, results from the deformable nature of foulants. This study investigates the combined impact of air scouring, shear stress, and consolidated residual fouling on compressible cake formation. A simple mathematical model is proposed that describes the net stress of attracted material on the membrane with a convective shear transport flux, which is dependent on applied shear stress and consolidated residual fouling. The convective flux is linked to the threshold flux, providing a straightforward relationship between step flux trials and cake formation. Results indicate that residual fouling reduces the effectiveness of membrane aeration and accelerates cake build-up. In addition, the cake's specific resistance decreases exponentially with the net attractive force of materials during its accumulation, influencing the compressibility coefficient. The proposed model identifies a threshold net material attraction flux, allowing fouling without exceeding an acceptable compressibility level.