No. 92: Water business in Japan and the world (11) (October 8, 2011)

Water treatment in Japan

You can drink safe water from a faucet in Japan. Raw water contains various impurities, and various technologies are being used to supply safe water. First, impurities in water collected from rivers are eliminated through deposition and sand filtration. Then, the treated water is chlorinated before it is delivered to households. Ozonation is sometimes added to make the purified water even better. Membranes are used to eliminate impurities of the purified water to produce ultrapure water for semiconductor production. If there is not enough water resources like rivers, desalination of seawater prevails. It is used to produce industrial water and in some isolated islands in Japan, but it is growing popular in such droughty areas as the Middle East and North Africa.

Two major methods of desalination exist. One is the evaporation method that distills seawater, and the other is the membrane method that eliminates chlorine using the reverse osmosis membrane. The latter attracts wide attention because it does not need energy. In 1993, a pathogenic organism that chloride could not deaden got mixed in with tap water and killed more than 400 people in the U.S. This accident promoted western countries to adopt the membrane method, and it is also growing popular in Japan.

Sewage collected from households is mixed with sludge containing microorganisms to resolve organic substances. The sludge undergoes separation by sedimentation to collect treated water. The membrane bioreactor (MBR) method that uses microfiltration membranes is also used in place of the method that needs separation by sedimentation of sludge. Demand for the MBR method will supposedly grow because it is easily manageable and it does not require a big facility, in addition to its high purification ability. The treated sewage is mostly discharged to rivers, and a small amount of it is reused as general service water.

In the above treatment processes, various kinds of companies, such as manufacturers of pumps, equipment, and membranes, engineering companies that design and construct facilities, and companies and municipalities that manage operations and facilities, are involved. The water business is growing bigger. (To be continued)