The aim of this special edition
[Application to water treatment using Membrane Separation System]
Hiroaki Ozaki

Department of Civil Engineering,
Faculty of Engineering,
Osaka Sangyo University

Since the method of reverse osmosis was developed in America in the early 1960s, the Membrane Separation System in the field of water treatment had limited utilities like desalting of seawater and ultrapure water until the early 1980s. In the late 1980s, water purification using membranes was tested in Europe and the United States. When the project "MAC21 plan of the water supply purification system using membrane" was promoted in Japan in 1991, diverse applications of this system including treatments of purified water, sewage, and wastewater have spread more widely than the conventional uses.
Thus, the membrane separation system is being paid attention these days. Since the membrane, which is being developed more recently, has a high performance and is suitable to various purposes, the system is highly efficient in separating almost all the substances regardless of organic or inorganic in property. It can be installed even in small-scale facilities although it has no advantage of scale. Furthermore, it has a unit function that can replace the existing one with a newly developed high-performance membrane module. Great hopes for the system using Membrane Separation System are as follows. It can produce high-quality water compared to other methods of water treatment. Its application meets the social need of reusing water for tight water demand. The conventional water system cannot only be simplified through innovation of the Membrane Separation System but also becomes sophisticated.
 Among various fields on which the Membrane Separation System is applied, water treatment for the purposes of supplying high-quality running water and minimizing water utilities through the use of membrane filtration has already installed the system on four hundred and several tens of plants. It is expected that larger-scale utilities will be built. On the other hand, the Membrane Bioreactor (MBR) is being employed as the major technology as a high-load biological denitrification process applies to excreta disposal. Factory effluent containing high concentration of organic substances is also an important subject to which MBR applies. In like manner, the application of the membrane separation system to a johkasou has many records because it is a small-scale system. However, its application to sewage disposal is delayed because of the water and membrane fouling effects. Because of the introduction of MBR, the application of the Membrane Separation System to a small-scale membrane sewage treatment plant has just been started. Whether it can be applied to a large-scale treatment remains a future challenge. Nevertheless, the application will spread more widely from the viewpoint of advanced treatment of sewage and reusing the treated water.
Many cases of the direct membrane separation system employed to factory effluent are present already, especially for the reuse of water and collection of valuable resources, as well as the treatments of electronic industries wastes and the plating effluent. Furthermore, the application to wastewater from incinerators, leachate and wastewater containing hazardous agent like healthcare liquid effluent is being advanced. It is considered that the application to fields which can take advantage of the capacity for advanced treatment will increase in the future.
Apart from the MBR, concentrated water must be treated because the Membrane Separation System is only a form of a solid-liquid separation. Physicochemical treatments like ozone and photocatalytic degradation and the development of combined microbial function in water purification are also significant challenges. The sole problem to be encountered is membrane fouling. Recently, a membrane which develops less fouling has been created. However, many cases show that replacement of membrane when fouling develops is a requisite in the actual treatment.
Although there are various challenges which need examining in the future, the Membrane Separation System is regarded from every direction as a water treatment technique of the 21st century. In order to build future local water circulation system, further improvements of the Membrane Separation System is expected.

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