Effect of the bubbling regimes on the performance and energy cost of flat sheet MBRs

Aeration in MBRs mitigates membrane fouling but the energy consumption for aeration is still one of the major operating costs for all MBRs in common use. However the effect of different hydrodynamic characteristics induced by different bubbling regimes in rectangular channels, akin to those in flat sheet MBRs, was investigated. The hypothesis was that there might exist an optimal bubbling regime to achieve an effective and economicalmethod to enhance the mass transfer coefficient, induce high wall shear stress while consuming only a very modest amount of air. This paper investigates the antifouling property of two different bubbling regimes on a laboratory-scale flat sheet MBR treating municipal wastewater at very low aeration rates. It was found that slug bubbles show better antifouling performance in flat sheet MBR under both shortterm high flux operation such as 36 h with a flux of 40 L m-2 h-1 and long-term moderate flux operation of 14 days with an initial flux of 24 L m-2 h-1. The notable finding is that the slug bubbling at low intensity (2.5 L/min) gave an excellent performance not only to limit the reversible fouling during the bubbling period but also to release the fouling that had occurred during the non-bubbling period. In contrast the fouling which accumulated during aeration with free bubbles at the same overall aeration intensity was greater. With increasing consideration being given to energy consumption, slug bubbling in flat sheet MBRs should be an attractive alternative method to free bubble. © 2011 Elsevier B.V.