Liquid concentration by direct osmosis

Liquid concentration minimizes packaging, transportation, handling and storage costs where the most commonly-used process is a thermal concentration process, such as evaporation and freeze concentration. The use of a thermal process results in substantial product losses through the degradation of flavors, aromas, and color. Steps may be taken to strip and recover volatile essences and oils but can add substantial costs. Utilizing a phase change to separate water from juice results in a hefty energy requirement and poses a continuing challenge in minimizing energy costs while maintaining product quality. Prior research has shown that reverse osmosis using standard commercial polyamide membranes can retain desirable solutes found in fruit juices. However, reverse osmosis can be viewed as energy-intensive relative to direct osmosis. Direct osmosis mimics energy-efficient osmotic processes utilized by biological systems avoiding the need for high-pressure or high-temperature and their material requirements such as stainless steel. This allows low-pressure plastics to be substituted for the stainless steel pumps and piping. A direct osmosis-based process can be lighter because of its low-pressure plastic components and quieter because it does not require high-pressure reverse osmosis pumps. Direct osmosis operates by using specifically-selected driving (a.k.a. draw) solutes to cause water to flow from the juice solutions through a semi-permeable membrane into the driving solutes. The driving solutes are in solution with an osmotic pressure higher than that of the juice solution and both solutions operate at atmospheric pressures. The high osmotic pressure from high concentrations of driving solutes can concentrate the juice solutions, potentially offering very high recoveries, an advantage compared to reverse osmosis where recovery is limited by operating pressure. High recovery means minimization of juice volume to be packaged, transported, handled and stored. The proposed research satisfies the USDA's strategic goal to enhance the competitiveness and sustainability of rural and farm economics by developing a non-thermal, membrane-based, liquid concentration process to replace existing thermal concentrating processes for fruit juices. The proposed non-thermal, membrane-based liquid concentration process requires the development of a direct osmosis polyamide thin-film composite hollow-fiber membrane. The direct osmosis process, when utilized with a direct osmosis membrane, will replace energy-intensive thermal concentration processes while producing high-quality concentrated juices by avoiding thermal degradation.