Energy Consumption in Terms of Shear Stress for Two Types of Membrane Bioreactors Used for Municipal Wastewater Treatment Processes

Two types of submerged membrane bioreactors (MBR): Hollow Fiber (HF) and Hollow Sheet (HS), have been studied and compared in terms of energy consumption and average shear stress over the membrane wall. The analysis of energy consumption was made using the correlation to determine the blower power and the blower power demand per unit of permeate. It was found that for the system geometries considered, in terms the of the blower power, the HF MBR requires less power compared to HS MBR. However, in terms of blower power per unit of permeate, the HS MBR requires less energy. The analysis of shear stress over the membrane surface was made using CFD modeling. Experimental measurements for the HF MBR were compared with the CFD model and an error less that 8 % was obtained. However, for the HS MBR experimental measurements were not made. Nevertheless as a proper validation was attained with the HF MBR, it was inferred that the CFD results for the HS MBR were accurate. A linear empirical correlation between the average shear stress and the blower power per unit of permeate was made. This relationship includes: the air flow rate, the geometrical dimensions of the MBR, the permeate flux and the membrane area and can be used for HF or HS MBR.