Flow Characteristics in an Airlift Membrane Bioreactor

Effect of changing the liquid level in an airlift membrane bioreactor of 0.7 m height, 0.24 m width and 0.18 m depth was studied both experimentally and by simulation. Three-dimensional simulations of the airlift membrane bioreactor were carried out at two different liquid levels above the membrane. The simulations were based on the two-fluid model with the standard k–? model for the turbulence. The results showed that by lowering the liquid level, the quality of mixing and uniformity of the velocity distribution of liquid phase in the riser would be improved while the shear stress on the membrane surface would be reduced. Higher shear stress on the membrane surface at high levels of liquid minimizes the extent to which particles settle on the membrane, thus, fouling will be reduced and flux of liquid through membrane will be enhanced. Moreover, it was shown that by lowering the liquid level, the fraction of air in the downcomers becomes lower.