Pilot-scale investigation, mathematical modeling, and simulation of osmotically assisted reverse osmosis (OARO) for the recovery of k-lactate solutions in food and beverage applications

Osmotically Assisted Reverse Osmosis (OARO) is an emerging membrane-based separation technology with strong potential for concentrating high-salinity solutions in industrial applications. This study investigates the performance of OARO in recovering potassium lactate (K-lactate) solutions, a high-osmotic solute widely used in the food and chemical industries. Thanks to its high osmotic potential, low reverse diffusion, and chemical stability, K-lactate is gaining attention as an ideal candidate for use as a forward osmosis (FO) draw solute. Pilot-scale experiments were carried out in collaboration with Hydrotech Engineering s.r.l. using a prototype spiral-wound membrane (SWM) module from Aquaporin A/S. The system was tested with feed concentrations ranging from 20 wt% to 60 wt%, corresponding to osmotic pressures ranging from 100 to 800 bar. Feed-side pressures were varied within the range of 20 to 28 bar, and sweep-side pressures were adjusted between 3 and 4 bar to assess their influence on process performance. Despite the challenging osmotic environment, stable water fluxes between 0.4 and 1.3 LMH were achieved. The results revealed significant performance limitations caused by concentration polarization, particularly on the sweep side. To further investigate system behavior and support process optimization, a predictive mathematical model was developed and validated using the experimental data. The model provided reliable estimates of flux and detailed spatial insights into membrane transport dynamics. This model was then applied to a case study involving OARO as a draw solution regeneration step in a FO–OARO hybrid system for coffee extract concentration. The system achieved reconcentration from 20% to 30%wt. Simulation results showed that the proposed configuration achieved a specific energy consumption (SEC) of 43.26 kWh/m³ of net permeate, representing a 9.8% reduction compared to benchmarked evaporation with mechanical vapor recompression (MVR) under comparable conditions. Although additional research is required to fully realize its potential, these findings demonstrate the technical feasibility and promising energy efficiency of OARO for processing high-salinity, value-added streams, positioning it as a scalable and viable alternative to conventional thermal concentration technologies.