A green approach for non-thermal concentration of skim milk by forward osmosis combined with membrane distillation for draw solution regeneration

As a cost-effective and sustainable technique, the hybrid forward osmosis (FO)-membrane distillation (MD) system has been conceptually demonstrated for the non-thermal concentration of skim milk and the regeneration of draw solution (DS). The FO unit was employed to concentrate skim milk, achieving up to a 2.91-fold based on total soluble solids (TSS) within 24 h. Meanwhile, the MD unit was used for the regeneration of the diluted DS from the FO process, restoring its high osmotic pressure. Enzymatic cleaning containing 0.1 % trypsin and 0.1 % lactase proved to be the most efficient cleaning method to restore water flux. The diluted DS from FO could be reconcentrated to its original level using MD process. The analysis of membrane fouling revealed that proteins and polysaccharides were the primary constituents of the fouling layer during the concentration of skim milk. The degree of membrane fouling was affected by the driving force and hydrodynamic conditions. Furthermore, the hybrid FO-MD system showed superior performance, with energy consumption nearly 50 % lower than that of traditional evaporator. Overall, this work provides a scientific and engineering foundation for the potential application of the FO-MD process in the non-thermal concentration of skim milk and the recovery of DS.