Performance evaluation of osmotically assisted reverse osmosis for potassium lactate draw solution recovery: Experimental assessment and process simulation

This study evaluates the application of multistage Osmotically Assisted Reverse Osmosis (OARO) for the recovery of potassium lactate (K-Lac) draw solutions used in Forward Osmosis applications. An experimental campaign was conducted to characterize OARO membrane performance across a wide concentration range (20–60 wt% K-Lac, corresponding to osmotic pressures of 100–800 bar) and operating pressures (20–28 bar). The results show stable water fluxes of approximately 1 LMH for concentrations between 20 wt%-40 wt%. However, the flux decreases progressively as the concentration increases, falling below 0.4 LMH at 50 wt%. Based on experimental data, a mechanistic membrane model was developed and implemented in a process simulator to design a full-scale system with the goal of re-concentrating K-Lac draw solution from 20 wt% to 30 wt%. Despite achieving the target concentration, the system requires a specific energy consumption of 43.3 kWh/m3. This energy demand approaches that of evaporation with mechanical vapor recompression, hindering the expected advantage of membrane processes. The findings highlight the technical feasibility but limited practical competitiveness of OARO for K-Lac solutions recovery under current performance constraints, emphasizing the need for advancements in membrane materials and process design to address the challenges posed by highly concentrated, viscous solutes.