The use of crossflow membrane separation technology in the beverage industry has gone from a 'unique processing' approach to a standard unit process for many manufacturers. Applications such as replacement of troublesome diatomaceous earth (DE) filters for juice clarification have been highly successful. Employing reverse osmosis (RO) for apple juice concentration produces potential shipping cost savings of over $2,000/day for a processor handling juice at a rate of 15,000 gallons per day. Using RO to purify dilution water has provided not only low sodium drinks but enhanced the taste and stability of beverage products. This paper discusses the membranes and membrane configurations available and the steps suggested to properly develop applications for crossflow membrane technology. Apple, grapefruit, lemon, cranberry, and grape juices as well as wine test results are presented. Applications performing clarification, pectin removal, and several concentration examples are discussed. A case of one bottler switching to a membrane based make-up water system is studied. Advances in membrane, membrane elements, and hardware to operate under the increased temperature and pressure requirements for some juice processes are also presented.
Crossflow Membrane Filtration VS. Conventional Purification Techniques
One major step in the acceptance of crossflow RO, UF, and MF into the beverage processing facilities is in having their process engineers understand and feel comfortable with a technology that looks and operates in a manner to which they are not accustomed. The usual definition of crossflow membrane filtration as the separation of the components of a fluid performed by polymeric semipermeable membranes through the application of pressure is not adequate. It is important they realize that crossflow membrane filtration is fundamentally different in design from the older technologies of depth and surface barrier filtration. In crossflow, the influent stream is separated by the membrane into two effluent streams: the 'permeate,' which passes through the membrane, and the 'concentrate,' which retains the solutes or suspended solids which have been rejected by the membrane. Although process engineers are intimately familiar with various forms of depth filtration and deionization, crossflow membrane filtration presents new potential but a new set of hydraulics also. Illustrations such as Figure 1 have helped to explain the basic process of crossflow filtration.
Crossflow Membrane Polymers
The wide range of beverage processing applications comprise a variety of fluid environments, some of which may be detrimental to certain polymeric materials. Operating conditions such as temperature, pressure, solution pH and cleaner compatibility must therefore always be considered. No one polymer will withstand the environments of all the possible juice processing applications where crossflow membrane processing can be applied, so several different membrane materials should be investigated to select the optimum for each application.