In membrane separation processes for liquid foods, as the molecular weight cut-off (MWCO) decreases from Microfiltration (MF) to Ultrafiltration (UF), Nanofiltration (NF), and Reverse Osmosis (RO):
Options:
(A) The pore size decreases and the required hydraulic operating pressure increases
(B) The pore size increases and the operating pressure decreases
(C) The osmotic pressure difference across the membrane approaches zero
(D) The permeation flux of pure water increases exponentially
Answer Key:
A
Step-by-Step Solution & Explanation
Across the membrane spectrum from MF to RO, effective pore size decreases from micrometers down to sub-nanometers (<1 nm). To overcome the tighter membrane resistance and significantly higher osmotic pressures of retained low-molecular solutes, the required hydraulic driving pressure increases from ~1 bar up to 40–80 bar.