Advances in membrane-based concentration: direct osmosis and membrane contactors

The process fundamentals and the role of operating conditions involved in direct osmosis (DO) and membrane contactors, such as osmotic distillation (OD) and membrane distillation (MD) are reviewed. Their main applications in concentration of liquid food and limitations compared with those of conventional de-watering processes - such as thermal evaporation, cryoconcentration and reverse osmosis - are discussed. The advantage lies in allowing very high concentrations (up to 65 degrees Brix) to be reached under atmospheric pressure and low temperature, thus avoiding thermal and mechanical damage.