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Release: May 13, 1997

NGK COMMERCIALIZED A CERAMIC MEMBRANE FILTRATION SYSTEM FOR WATER TREATMENT PLANT

NGK Insulators, Ltd. (President: Masaharu Shibata, Head Office: Nagoya) developed a ceramic membrane filtration system for a water treatment plant applying its original ceramic membranes, which have been already utilized in the medical and food industry. The newly developed system was shipped to the water treatment plant located at Miwa-cho, Amada-gun, Kyoto in March 1997. This is the first water treatment system which employs ceramic membranes in Japan, and is supposed to start operating in February, 1998.

This system consists of four membrane modules, and each module contains 150 ceramic membranes. They are Alumina-made monolithic membranes of 100 cm in length and 3 cm in diameter. Their horizontal section resembles a slice of lotus root (Attachment 3). The largest pore diameter on the membrane is 0.1 micro meter, and the gross area of membrane is 288 square meters. The treatment capacity is 424.6 cubic meters/day.

NGK acquired certifications from Japan Water Research Center for the technique to manufacture seven types of membrane module which ranges in area from 18 square meters to 73 square meters. Based on such techniques, NGK has been manufacturing products to be suitable for various amounts of water purification at medium and small size water treatment plants, and is planning to enlarge their sale following the shipment to Miwa-cho.

1. Background

  1. The water treatment for a small water-supply system , in general, applies slow sand filtration or coagulation sedimentation with rapid sand filtration. Due to the timber cutting in the water source area and the enlargement of residential area, the deterioration of raw water caused by earth, sand, and waste water is increased. As a result, the system is required to function well with poor quality water. In addition, due to the population growth and the merge of several small water-supply systems, the volume of raw water to be treated has been enlarged. Therefore, there is difficulty in finding the building site to construct water treatment plants which can deal with such a large amount of water. This requires the compactness of system. The lack of manpower in charge of small water-supply system seeks to simplify maintenance and to operate the system automatically.
  2. NGK has engaged in the development of membrane filtration technique since 1989 to solve the above-mentioned problems. NGK also has joined the project conducted by the Ministry of Health and Welfare, "MAC21 Project" (from November, 1991 to March, 1994), which aimed to introduce membrane filtration technique into medium and small size water systems since 1991.

2. Advantages of Ceramic Membrane

  1. A ceramic membrane keeps good filtration quality in the event of fluctuation of raw water turbidity.
  2. Membrane separation does not require a sedimentation tank and a rapid sand filter; therefore, a treatment plant employing membrane separation can be constructed in a small building site, which is one half or one third of that required for a slow sand filtration or coagulation, sedimentation and rapid sand filtration plant.
  3. Since fine pores on a ceramic membrane are uniformly laid out, the suspended solid including bacteria can be precisely removed; as a result, the filtrate has high purity.
  4. Ceramic membrane has ceramic property, which is superior in corrosion resistance; therefore, the membrane does not change in quality.
  5. Ceramic membrane is superior in chemical resistance; therefore, it has a large selection of chemicals to be applied as abstergent compared with polymeric membrane. As a result, the performance of the membrane can be recovered close to the initial condition.
  6. Ceramic membrane has an asymmetrical structure consisting of three layers, which are filtering layer, intermediate layer, and support layer (from the finest). The pressure drop of such asymmetrical structure is lower than that of symmetrical structure of other membrane, which means that the ceramic membrane has better recovery.
  7. Since ceramic membrane is superior in mechanical strength and its structure does not deteriorate for years, it does not have to be replaced for a long time.

3. Advantages of Ceramic Membrane Filtration System for Water Treatment Plant

  1. Good quality of filtrate
    Due to the high separation performance by ceramic membranes, the system can remove all suspended solid and bacteria, such as coli bacilli, which are bigger than pores on the membranes. In addition, this system does not require prechlorination; therefore, formation of chlorine organic compound (Trihalomethane) , which is caused by organic matters and chlorine, can be restrained.
  2. High recovery of membrane filtration performance by NGK's unique backwash system
    By making the use of mechanical strength of ceramic membrane, the backwash system by using backwash water and compressed air is introduced into the ceramic membrane filtration system. Because of the backwash system, the ceramic membrane performance can be recovered well, which makes it possible to operate the filtration system continuously for six to twelve hours. The volume of filtrate used as backwash water is small; therefore, the water recovery rate can maintain approximately 99%. In the event of rapid fluctuation of raw water turbidity caused by typhoon and heavy rain, the stable operation is possible since the ceramic membrane filtration performance is recovered well by the backwash system.
  3. Easy maintenance
    The simplification of coagulation eliminates the need for complex injection control of coagulant. The microflocculation and membrane filtration system are also fully automated and do not need manpower. The membrane filtration system requires chemical cleaning and replacement of membrane; however, in case of ceramic membrane filtration system, the chemical cleaning needs to be done once or twice a year, and the replacement of membrane is estimated once in twelve years because ceramic membrane has high mechanical strength and excellent performance recovery by the chemical cleaning.

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