The large desalination plants around the world are running with RO technology. RO is long established as a large-scale industrial membrane process. Reverse osmosis systems require almost exclusively electric energy for pumping and recirculating, whereas evaporative systems require steam in addition to electric energy for pumping. Overall, reverse osmosis systems require less energy than evaporative systems per unit of water removed from the product. Reverse osmosis is very energy-efficient, because it typically operates at ambient temperature (no heating or cooling required) and, most importantly, there is no phase change requirement for water removal, as in evaporative processes. They are also more flexible and easier to modify or upgrade than conventional evaporative systems. Due to their relative simplicity, reverse osmosis systems have shorter come-up and shutdown time. Since reverse osmosis systems do not require steam, evaporators, and condensers, they require much less floor space and equipment than evaporative systems. Thus, reverse osmosis has a minimal effect on the quality characteristics and nutritional value of the finished product, especially when compared to evaporative concentration where inevitably there is heat degradation, as well as flavor and nutritional losses. It does not impart pH or chemical changes in the product and, since no significant heating is required, there is no heat degradation of the product. Reverse osmosis is a very efficient process, allowing for the simultaneous concentration, fractionation, and purification of the product and the accomplishment of multiple tasks in a single unit operation. Katsanidis, in Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003 Performance Comparisons Also, these membranes exhibit better recovery of valuable compounds in processed liquids, e.g., aroma compounds. This new generation of membranes gave food processors the opportunity to apply more rigorous cleaning routines and greater plant sanitation. During the 1980s a wide variation of thin-film composite membranes appeared on the market. Until recently, the application of RO in the food industry has been based on the use of cellulose acetate membranes. For RO to take place, it is essential that a membrane has the right chemical nature (polar and nonpolar effects) and that its pores are of appropriate size and number (steric effect).Īlthough RO is mainly applied in the production of potable water from sea and brackish water, the use of RO in food processing is growing steadily. According to this mechanism, permeation occurs due to the preferential sorption of constituents from fluid mixture and their permeation through the porous membrane. Like other membrane processes, RO offers flexibility in different applications and scales, RO concentration is best explained as the mechanism of preferential sorption capillary flow. This is of utmost importance in concentrating liquid foods. Also, RO concentrated fluids are not subjected to any heat damage or losses in aroma compounds, as has occurred in other concentration processes. Compared to other competing processes, RO is more economic in concentrating diluted solutions and for medium concentrations. RO is an energy-saving process as removal of the solvent does not require change in phases. RO has several advantages compared to other concentration technologies. Therefore, RO is classified as a concentration process. In practice, RO membranes retain 95–99% of the dissolved solutes (organic and inorganic) from the feed stream into the concentrate, while the permeate can be considered as high-quality water. Reverse osmosis (RO) is essentially a pressure-driven membrane diffusion process. ![]() Abd El-Salam, in Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003 Introduction
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