Investigation of reverse osmosis technology for wate quality management

Reverse osmosis (RO) is gaining worldwide acceptance in both water treatment and desalination applications. It is a pressure-driven process whereby a semi-permeable membrane rejects dissolved constituents present in the feed water. This rejection is due to size exclusion, charge exclusion and physical–chemical interactions between solute, solvent and membrane. The process efficiency depends on operational parameters and on membrane and feed water properties. The most commercially available modules are spiral-wound and hollow fiber. The latter has an extremely high packing density and thus high permeate production rates but is more prone to fouling. The membranes can be either asymmetric containing one polymer layer or composites consisting of two or more layers. The functional groups introduced into the polymer structure control the valence and strength of the membrane charge while the degree of adsorption of dissolved species is determined by membrane hydrophobicity, charge and roughness affect. Recently, high area elements have become available, reducing footprint and the number of pressure vessels. So far, most commercially available RO membranes are still asymmetric cellulose type (cellulose acetate, triacetate, cellulose diacetate or their blend) and TFC type. The asymmetric cellulose RO membrane is prepared by phase inversion method, while the TFC RO membrane is fabricated by forming a dense aromatic polyamide barrier layer on a microporous support such as polysulfone via an interfacial polymerization process. Compared with cellulose membrane, the TFC aromatic polyamide membrane exhibits superior water flux and salt rejection, resistance to pressure compaction, wider operating temperature range and pH range, and higher stability to biological attack Therefore, it dominates RO membrane field nowadays. Despite its many advantages, one of obstacles to the widespread use of TFC polyamide RO membrane is the proneness to fouling. Fouling is a process where solute or particles in feeding water depositonto RO membrane surface in a way that causes flux decline and affects the quality of the water produced. Although the performance of fouled RO membranes can be partially restored by appropriate cleaning method, it will inevitably increase operation difficulty and decrease membrane’s life time, which will be translated into higher costs. In this study, application of reverse osmosis technology in water treatment it was discussed.

Keywords:

Reverse osmosis , semi-permeable membrane , polymer layer , TFC RO membrane