Critical stability conditions in crossflow microfiltration of skimmed milk: transition to irreversible deposition

Abstract

An experimental “cyclic” methodology was used to evaluate critical operating conditions for crossflow microfiltration (MF) performance. It consisted of successive cycles of increasing and decreasing operating parameters ((i) Δ P at constant τ w, (ii) J at constant τ w, (iii) τ w at constant Δ P, (iv) τ w at constant J; with Δ P, transmembrane pressure, τ w, wall shear stress and J, permeation flux) during which attention was paid to the evolution of permeability and selectivity of the separation. This methodology was applied to skimmed milk MF using a tubular ceramic membrane (0.1 μm mean pore diameter) for the separation of casein micelles from soluble proteins. The system showed a limiting flux which depended on the hydrodynamic conditions. The hystereses observed suggested assumptions about the alteration of casein micelles deposit characteristics (thickness, compressibility, structure, etc.) and made it possible to determine a critical ratio of permeation flux over efficient wall shear stress ( J/ τ weff), under which performance were satisfactory. Above this ratio, the consolidation of the deposit due to its compression under high transmembrane pressure led to irreversible cake structure and then to low permeation fluxes and soluble protein transmission.