A preliminary comparison between nanofiltration and reverse osmosis membranes for grape juice treatment

Nanofiltration (NF) and reverse osmosis (RO) systems were compared using gr ape juice as feed solution. The initial permeate flux (J) was 7.4, 8.1, and 1.7 dm(3) m(-2) h(-1) with NF membranes DS and DK, and RO membrane SWC, re spectively. The exponential decay of J in the above NF and RO membranes was characterized by a fouling index equal to 0.16, 0.22, and 0.24, respective ly, The permeability of NF membrane DS doubled by increasing the working pr essure from 32 to 45 bar. Despite the additional power (+30%) required to w ork at the higher pressure value there was an energy saving per unit permea te of approximately 35%. The working pressure and temperature affected the selectivity of NF membranes. As expected, a direct relationship between mem brane permeability and working temperature occurred; the permeate flux of N F membrane DS increased by about 3% per degree of temperature rise. (C) 200 1 Elsevier Science Ltd. All rights reserved.