Optimizing protein-cell separation in submerged membrane bioreactor for clarification

Membrane fouling hinders protein-cell separation efficiency in membrane bioreactors. A comprehensive understanding of multi-variable fouling mechanisms and optimized backwashing (BW) strategies for mixed foulants are not well characterized. Here, we present the first systematic investigation using fractional factorial design (FFD) to reveal yeast-bovine serum albumin (BSA) fouling dynamics, analyzing five critical factors: yeast and BSA concentration, BW flux, BW duration, and BW cycle. The experiments reveal that yeast concentration is the dominant factor dictating flux reduction through cake layer formation, while BSA exhibits minimal significance on flux in the presence of yeast. Elevated BW flux enhances flux while simultaneously reducing BSA transmission, establishing a fundamental operational trade-off between fouling control and product recovery. Short-duration, high-frequency BW effectively controls fouling, yet excessive cleaning compromises protein transmission. Under optimal BW conditions (125 L m⁻² h⁻¹ flux for 5 s every 5 min), the system successfully maintained a stable flux of 80 L m⁻² h⁻¹ with 81 % BSA recovery over 140 min of operation, tested at BSA concentration (8.66 g L⁻¹), demonstrated a 20–25 % performance improvement over non-BW condition. Furthermore, BSA concentrations up to 40 g L⁻¹ sustained fluxes of 72–80 L m⁻² h⁻¹ with 30 % protein transmission within 30 min. The concentration-resilient performance indicates significant process intensification potential with reduced footprint and downstream integration for high-titer protein recovery. Superior performance requires multi-variable optimization to balance cleaning intensity and timing for efficient protein-cell separations.