OSMOTICALLY ASSISTED REVERSE OSMOSIS FOR AQUEOUS SOLUTION CONCENTRATION: PILOT TESTS, MODELLING AND SCALE-UP

Osmotically Assisted Reverse Osmosis (OARO) is attracting growing interest as a membrane process capable of concentrating aqueous solutions beyond the limits of conventional reverse osmosis (RO). This PhD research project explores its potential through pilot-scale experiments, the development of dedicated membrane module prototypes, mathematical modelling, and process simulations, with a focus on high- salinity brines and resource recovery. Initial trials with films used in commercial RO membranes revealed poor performance due to severe concentration polarization and mass transfer resistance, while forward osmosis (FO)-based modules displayed more favourable hydraulic properties but suffered from structural deformation under pressure. Building on these findings, novel 4040 spiral-wound modules specifically designed for OARO were developed and tested with NaCl solutions up to 226 g/L. These modules delivered stable fluxes between 1 and 2 L/(m2·h) under harsh operating conditions, though membrane deformation at high pressure was found to increase pressure drop and reduce flux. To interpret and optimize performance, a mathematical model was formulated and validated with pilot-scale data, accurately describing flux variations along the module by accounting for hydraulic losses, osmotic pressure gradients, and geometry. Process simulations of multistage OARO for Zero Liquid Discharge (ZLD) indicated that, while brine concentrations comparable to High-Pressure RO (HPRO) can be reached, energy consumption is substantially higher, limiting practical deployment. Finally, OARO was assessed for potassium lactate recovery in the food sector, demonstrating technical feasibility but prohibitive energy requirements. Overall, the results highlight OARO’s potential but also underline the need for significant advances in membrane and module design to enable industrial application.