فصلی از کتاب در مورد اسمز معکوس
Abstract
20-1- Introduction
20-2- Membrane Transport Models
20-3- Concluding Remarks
References
INTRODUCTION
The seawater or brackish water desalination process by reverse osmosis (RO) has been known for many years. Loeb and Sourirajan (1962) developed a method for making asymmetric cellulose acetate membranes, which provide excellent scope for the application of this process for practical purposes due to their relatively high water fluxes and separation efficiency (Williams, 2003). Among the synthetic polymeric membranes on the market is the aromatic polyamide with pendant sulfonic acid group proposed by DuPont (Uemura and Henmi, 2008). It has a high rejection performance, which can be used for single-stage seawater or brackish water desalination. The development of new-generation membranes such as thin-film, composite (with an in situ monomer condensation method), nanostructure, and mixed matrix membranes that can have much higher water flux and solute separation properties has resulted in many additional RO applications such as wastewater treatment, e.g., in the galvanic industry, for water softening, and for food and beverage processing (Bhattacharyya and Williams, 1992). Nowadays, there are growing activities in developing RO membranes from inorganic materials such as ceramic membranes (e.g., a-alumina supported MFI-type zeolite membranes) due to their thermal, mechanical, and chemical properties. Zeolite membranes could be an alternative for polymeric membranes in treating various kinds of water and wastewater, and/or for the separation of organic mixtures (Lee et al., 2011). One of the most important applications of RO is water treatment for producing high-quality water using high-salinity geothermal water, surface water, peat water (natural brown water), as well as wastewater (industrial, municipal water) treatment. RO is capable of removing low concentration bioactive pollutants such as pesticides and hormones from surface water (Hofman et al., 1997). Potential application of the RO process is the concentration of various fruit juices (orange, apple, pear, grape, tomato juices) and preconcentration of sugar juices. This process is also widely applied in the dairy industry for, e.g., recovering protein, defatting whey, and concentrating milk and whey as alternatives to conventional processes (Pouliot, 2008). Other applications of the RO process are, e.g., alcohol removal from fermented beverages and separation of organic mixtures, including alcohols and hydrocarbon (azeotropic, isomeric) mixtures (Koops et al., 2001). Fouling/biofouling is regarded as the most serious problem in the RO process, depending on the water composition used for separation. Reasons for fouling of the RO membrane are chemical (adsorption of organic materials) and biological fouling (microbe adsorption by hydrophobic or electrostatic interaction, deposition of exhaust material of biological metabolism) (Uemura and Henmi, 2008). This is why it is important to produce a low-fouling property membrane with high water flux and stable operation.