The detailed structures and distribution of enzymatically active magnetic-responsive dynamic layers (EnzSP) were investigated for the first time in a crossflow superparamagnetic biocatalytic membrane reactor (XF-BMRSP). The trade-off between a higher mass transfer rate, lower fouling tendency, and preventing washout of the dynamic layer, highly depends on the balance of the various forces that act on the EnzSP. The real-time visual inspection of the biointerface was realized through the design and fabrication of an adapted crossflow system, guided by computational fluid dynamics (CFD) simulations. Time-resolved images of the dynamic layer under a broad range of operational conditions was obtained using fluorescence microscopy.

The deposition, dispersion and stability of the dynamic layer was mainly governed by the external magnetic force. The shear force did not cause significant particle washout when a buffer solution was recirculated without permeation even under a turbulent flow regime (6.4 cm/s ∼ Re = 5200). The removal of the external magnetic force after initial magnetic immobilization of the EnzSP, or the substitution of a smooth flow velocity by the propagation of an impulse flow, significantly affected the stability of the dynamic layer.

Although membrane fouling occurs at the membrane-solution interface, where a laminar flow regime prevails, most membrane fouling models are based on turbulent flow. Therefore, the detailed, time-resolved images obtained here can provide solid foundation for the development of theoretical models that can describe the membrane fouling under the more representative laminar flow regime.