Innovation and optimization of aeration in free bubbling flat sheet MBRs

Abstract

Free bubbling in flat sheet MBRs has been widely used in water treatment to control membrane fouling, however, the associated aeration cost discourages its wider application. To counter this drawback an innovative design of the aeration system is proposed and its evaluation indicates significantly high potential. The guiding aim is the establishment of sufficient shear stress in all membrane channels at an economical specific air demand (SADm). Based upon a validated Computational Fluid Dynamics (CFD) study, hydrodynamic features including shear stress, bubble size and the distribution of bubbles across neighboring channels were predicted for two designs. For both a mini 100-sheets commercial FSMBR (size of plates 448 mm × 245 mm) and a full-scale standard unit with 1800 mm × 490 mm plates, it was shown that sufficient hydrodynamic effect is induced with our modified free aeration design in a manner that moves beyond seeking to achieve bland uniformity between channels. The optimal configuration featured a channel gap at 5 mm and an aerator with an additional large side nozzle operating at an inlet velocity of 2.6 m/s. Such an arrangement would cover 12 channels. Through optimization the air consumption was successfully reduced giving a SADm of 0.28 Nm3m-2h-1, corresponding to 46% reduction with respect to traditional industrial usage of 0.51 Nm3m-2h-1.