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

Nanofiltration (NF) and reverse osmosis (RO) systems were compared using grape juice as feed solution. The initial permeate flux (J) was 7.4, 8.1, and 1.7 dm3 m−2 h−1 with NF membranes DS and DK, and RO membrane SWC, respectively. 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, respectively. The permeability of NF membrane DS doubled by increasing the working pressure from 32 to 45 bar. Despite the additional power (+30%) required to work at the higher pressure value there was an energy saving per unit permeate of approximately 35%. The working pressure and temperature affected the selectivity of NF membranes. As expected, a direct relationship between membrane permeability and working temperature occurred; the permeate flux of NF membrane DS increased by about 3% per degree of temperature rise.