Next-Generation Fibrous Media for Water Treatment
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porous symmetric membranes and phase inverted media as asymmetric membranes. Figure 2a shows the top view of an electrospun membrane and Figure 2b shows its cross section.
Fibrous Media for Water Treatment
Fibrous Media in Separation Technology
Satinderpal Kaur, Renuga Gopal, Wun Jern Ng, Seeram Ramakrishna, and Takeshi Matsuura Abstract Fibrous media in the form of nonwoven filters have been used extensively in water treatment as pre-filters or to support the medium that does the separation. Nonwoven media are composed of randomly oriented micron-size fibers and provide a one step separation as a substitute for conventional processes comprising chemical addition, flocculation, sedimentation, and sand filtration. At present the use of nonwoven filter media is limited to pre-filters and is not used further downstream as high performance filters. However it is expected that by reducing the fiber size in the nanometer range, higher filtration efficiency can be achieved. With the advent of nanotechnology, the ease of producing high quality nano scaled fibers is now a reality. Recent advancements in nanofibrous media through surface modifications have shown that nonwoven media can be used beyond the prefilter stage. Furthermore the pore size of the filter media can be controlled through modification of fiber size and thickness of membranes. These nanofibrous membranes possess high surface area and large porosity leading to high flux, low pressure membranes. This article highlights important opportunities and challenges associated with developing nanofibrous media for water treatment. In addition, we have attempted to capture a snapshot of this rapidly developing new area of fibrous media for water treatment for the benefit of the wider membrane community.
Introduction Although the earth is made up of 75% water, obtaining water for drinking and industrial purposes is still not easily achieved. A tedious process of water clarification is required, involving a lot of capital and energy. However the development of phase inverted membranes and fibrous depth filters has simplified and accelerated the production of “clean” water.1 Both phase inverted membranes and fibrous depth filters selectively block the passage of certain components of a mixture and permit passage of other components. Property comparisons are made for these two types of filters in Table 1. One way of classifying filters is by morphology or structure. Filter structure is very important as it dictates the separation and permeation mechanism and consequently the application as well. There are two different filter structures, namely symmetric and asymmetric.2
When a membrane has the same chemical and physical structure throughout, it is called a symmetric membrane; when it has a varying chemical and physical structure throughout its thickness, it is called an asymmetric membrane.3 Figure 1 reflects this classification. Currently, the fibrous filter media are distinguished as
Throughout the history of filtration and separation processes, many variants of
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