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High and stable permeate flux can be obtained with shear-enhanced nanofiltration (NF) in model dairy wastewater treatment. In order to sustain such flux in long-term operation, critical fouling conditions should be studied and an optimum flux needs to be selected. Based on resistance-in-series and particle deposition models, a threshold flux was proposed to make a distinction between low and high fouling rates. At and below threshold flux, adsorption and reversible fouling are almost stable, and the fouling rate is low and nearly constant, irrespective of permeate flux; while above it, flux declines markedly with increasing flux mainly due to incremental reversible fouling. Flux remained quite stable with slight fouling (<5%) in 6h operation at threshold flux, up to 6.1×10⁻⁵ms⁻¹ at shear rate of 1.81×10⁵s⁻¹ for diluted milk. Flux anomaly occurred in operations above threshold flux and fouling was more important …