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Water Plaza Kitakyushu

Leader in Water Recycling R&D

Japanese tend to murmur mottainai (too good to waste) at the sight of something perfectly usable being discarded or wasted – an apparent manifestation of their traditionally held respect for nature and other things. Even for the people in a rainy and water-rich country, domestic wastewater being dumped into rivers and the sea without being recycled looks plainly wasteful (mottainai). It is no wonder then that Japan has been doing extensive research on water-recycling and reuse technologies with the aim of dealing with global water problems in general, not just recycling water in Japan.

Demonstration Plant Open to World


A full view of Water Plaza Kitakyushu. Buildings on the left connected with piping are a demonstration plant for water recycling and reuse. Buildings on the right are test beds for technological research and development.

"Water Plaza Kitakyushu," located in Kitakyushu City, Fukuoka Prefecture, is a demonstration plant for water recycling and reuse built in 2009 by a confederation of Japanese government organizations, the city, and industrial material and plant equipment manufacturers. For their part, the member companies have also established the Global Water Recycling and Reuse Solution Technology Research Association (GWSTA) with the specific aim of developing original techniques and sending out information to the world on expertise in ways of managing a water-recycling system. Water Plaza is not a mere demonstration plant for water recycling. It is one of the largest research centers in Japan aimed at solving global water problems.


Bottled water (from left to right): raw sewage, seawater, and recycled water. Sewage and seawater each go through two rounds of filtration to be recycled into clean water.

Enlarge photo

Sitting on a site of about 6,000 square meters, Water Plaza has a pair of facilities – a demonstration plant equipped with advanced water-recycling and reuse systems, and test beds for technological research and development. The plaza is unique in that it is testing the world's first state-of-the-art technology for improving the efficiency of producing recycled water by mixing seawater with water recycled from sewage and purifying it.

The plaza daily collects 2,000 tons of water – 1,500 tons of domestic wastewater, equivalent to living drainage from about 6,000 people, and 500 tons of seawater. Of the total, 300 tons of water are set aside for experimental purposes and the remaining 1,700 tons are treated to produce 1,400 tons of recycled water. Currently, the recycled water is being supplied to a power plant 2 kilometers away to be used for its boilers fueled by LNG.

Nano-level Technology for Purification

Water is filtered through membranes made with Japan's leading-edge technology. Wastewater is filtered through ultrafine holes punched in the membrane, with their diameter measuring a 10,000th to a millionth of a millimeter each.


Real-size plane membranes used in the first round of filtration of sewage. With holes as fine as nano levels in diameter, they are capable of capturing almost all impurities.

In the case of sewage, it is first treated with microorganisms to dissolve organic sludge, then filtered through the membrane to do away with remaining particles, including microorganisms, and becomes clear water.

In the case of seawater, an ultrafiltration (UF) membrane is used to eliminate particles such as bacteria. Both sewage and seawater finally go through yet another membrane system to eliminate salt and ions to be recycled into drinkable water.

The membrane used in the second stage of filtration has nano-level holes of a millionth of a millimeter in diameter, the result of cutting-edge technology. The membrane is rolled up multiple times into the shape of a tube measuring 8 or 16 inches in diameter. As water cannot filter through the membrane due to the much too fine holes, water is pressurized with a pump to force its way through the holes to become drinkable.

Drinkable Water

Water thus recycled is clear, colorless and drinkable. Recycled water not only meets the Japanese government's quality standards for tap water in terms of chlorine ions, total organic carbon and residue on evaporation, but it also contains less than half the standard levels of total organic carbon and residue on evaporation.

photo photo
Left: A membrane system used to filter seawater. Once filtered through the membrane, seawater becomes drinkable.
Right: A real-size model membrane 16 inches in diameter. The cross-section of the rolled-up membrane looks like that of a layer cake.

The recycling system boasts a high recycling ratio of more than 80%. It could well be a product of the Japanese trait that does not tolerate any waste, trying to use even the residue of wastewater. All of this is a result of extensive research to utilize wastewater to the fullest.

The key was to put wastewater extracted from sewage into seawater having gone through the first round of filtering. As a result, the overall recycling ratio is improved compared with conventional methods and the salt content of diluted seawater is also lower, making it possible to halve the pumping pressure needed to filter water through the fine-hole membrane to eliminate the salt in the second stage of filtering. Those measures have ensured an efficient, low-cost water-recycling system.

In the test beds in the plaza compounds, five firms, including water treatment companies, have set up pilot plants. The companies are vying to develop even better water-recycling systems with greater energy conservation and cost reduction, including the development of chemicals able to sterilize membranes at a lower cost.

High Hopes for Solving Global Water Shortage

Since it opened, Water Plaza has received 750 foreign visitors from 54 countries. The largest number of visitors came from China, followed by those from Southeast Asia and the Middle East.

Rapidly growing countries are suffering from serious shortages of water as a result of population growth and rising demand for industrial water. If these emerging countries are able to supply their industries with recycled water, then they can use saved water for agricultural irrigation and other purposes, at the same time enabling them to dispose of the massive amounts of domestic wastewater swelling with urbanization. That is a “sustainable city” Water Plaza is aiming for.

The Water and Sewer Bureau of Kitakyushu has been sending officials to Phnom Penh in Cambodia to help their local counterparts learn about the Japanese city's advanced water management technology, making it possible to reduce water leakage by an astonishing degree and winning international acclaim for this and other achievements.

The international community is now looking at Japan with rising expectations for a viable solution to global water problems.

(January 2013)

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