Filtration performance of biofilm membrane bioreactor: Fouling control by threshold flux operation

Membrane fouling is the major factor that restricts the furtherly widespread use of membrane bioreactor (MBR). As a new generation of MBR, biofilm membrane bioreactor (BF-MBR) demonstrates high treatment efficiency and low sludge growth rate, however the filtration performance improvement and membrane fouling control are still the challenges for its further development. This work investigated the filtration performance using resistance in series model and membrane fouling control via threshold flux for BF-MBR. At first, the flux behavior and filtration resistance under various operating conditions, including agitation speed, membrane and TMP, were explored by resistance in series model. Because of the desirable anti-fouling capacity, UP100 and UP030 had the high threshold flux (100 and 90 L m⁻² h⁻¹) and low irreversible fouling resistance (1 and 1.3 × 10⁻¹⁰ m^-1). Higher shear stress produced by higher agitation speed could reduce membrane fouling, while greatly promote the threshold flux (138 L m⁻² h⁻¹) and membrane cleaning efficiency (96%). Moreover, increasing shear stress or selecting membrane with large pore size could decrease the fouling rate and raise the threshold flux. As for TMP, high TMP reduced the removal rate for organic and nutrient, and enhanced the irreversible fouling. Besides, the aerobic-BF-MBR (101 L m⁻² h⁻¹ and 1.3 × 10⁻¹⁰ m^-1) with lower foulant concentration had a better filtration performance than anoxic-BF-MBR (90 L m⁻² h⁻¹ and 1.5 × 10⁻¹⁰ m^-1). Additionally, the long-term tests with 10 cycles were conducted to evaluate the industrial application value of BF-MBR (45–58 L m⁻² h⁻¹). This work provides the technical support for sustainable filtration performance of BF-MBR.