Osmotic Distillation and vacuum membrane Distillation for juice concentration: A comparison in terms of energy consumption at the permeate side

In this work, Vacuum Membrane Distillation (VMD) and Osmotic Distillation (OD) were compared in terms of the energy consumption needed to recover the permeates produced during juice concentration. In particular, the recovery of the vapor permeate in VMD and the removal and recovery of the condensed permeate from the brine stream used in OD (brine regeneration) were considered. The calculations were made at parity of operating conditions at the feed side (28 °C and 30 °Bx) and of concentration factor achievable (same concentration performance of the two membrane operations), based on available literature data. The high osmotic pressure of the brine used in literature (CaCl 45 wt%) did not allow to apply nanofiltration (NF) or reverse osmosis (RO) for removing the condensed permeate. Therefore, the brine regeneration involved the permeate evaporation and its successive condensation, with an energy consumption per produced permeate higher (4893 J/g) than that calculated for the VMD unit (3090 J/g).