Face CASE31 Face

Facilities Control Department, Business Administration Division, Kumamoto Factory, Honda Motor Co., Ltd.

Akio Zaitsu, Manager of the Facilities Control Department, Business Administration Division, Kumamoto Factory

Akio Zaitsu, Manager of the Facilities Control Department, Business Administration Division, Kumamoto Factory

Our approach to keeping local groundwater abundant

 The reason why Kumamoto is called the “water capital” is its abundant groundwater. Rainwater falling in the Mt. Aso area seeps into the ground and is purified through groundwater systems. The water takes on dissolved minerals and reemerges in locations throughout the prefecture. At the Kumamoto Factory, both industrial and domestic water were once completely sourced from groundwater.
 "It’s not that unusual around here. Actually, the public water supply in Kumamoto City is all supplied by groundwater," said Akio Zaitsu, Manager of the Facilities Control Department, Business Administration Division, Kumamoto Factory.
 However, even abundant natural resources can be depleted in the long run if they are used without discretion. Concerned about this matter, Kumamoto Prefecture began some 20 years ago to call on entities in the prefecture to conserve groundwater in an attempt to use the natural resource more sustainably. In response to this request, the Kumamoto Factory mapped out a plan to reduce groundwater use.
 "We came up with the idea to use rainwater for industrial purposes in our plants," Zaitsu said.
 The Kumamoto Factory was already using rainwater at the time, but now it planned to increase its use dramatically, to 100,000 tons annually. There were precedents for using several hundred to several thousand tons of rainwater per year, but based on common sense, it seemed impossible to reach a volume as large as 100,000 tons annually. However, Zaitsu had something in mind.
 "We could use one of our balancing reservoirs on the premises. I thought that, if we used the water in our No. 1 Balancing Reservoir, which never dries up, we could secure around 100,000 tons of industrial water annually," Zaitsu explained.
 A balancing reservoir is a pond used to temporarily store rainwater that falls onsite and discharge it gradually to prevent flooding in downstream areas. While balancing reservoirs are commonly built near factories and industrial complexes, The Kumamoto Factory's No. 1 Balancing Reservoir, which takes advantage of the natural topography, boasts an unusually large capacity of up to 70,000 tons. Moreover, this reservoir remained filled with water throughout the year.

No. 1 Balancing Reservoir

No. 1 Balancing Reservoir

Well system next to the No. 1 Balancing Reservoir. Rainwater is drawn into a tank below this building and conveyed to the factory.

Well system next to the No. 1 Balancing Reservoir. Rainwater is drawn into a tank below this building and conveyed to the factory.

The Kumamoto Factory’s patented rainwater purification system combines biological treatment, activated carbon filtration, and UV sterilization.

The Kumamoto Factory’s patented rainwater purification system combines biological treatment, activated carbon filtration, and UV sterilization.

Investment in rainwater facilities becomes an endeavor in environmental stewardship, not short-term profits

 And so Zaitsu set about planning to use the rainwater stored in the reservoir as coolant for factory equipment. The challenges he faced were how to draw rainwater from the reservoir to the equipment that would use it, and how to purify the water to a level that would allow it to be used as coolant.
 The Kumamoto Factory decided to use an existing well system located next to the No. 1 Balancing Reservoir to draw the water. By drawing rainwater to the existing route used for delivering pumped groundwater to factories, the factory realized significant cost savings, as compared to building a new water drawing system.
 For water purification, Zaitsu first considered using chemicals but then abandoned the idea, because he found that, as a negative effect, it would cause the salt concentration in the water to exceed the regulatory limit. "So we tried biological treatment, where microbes are bred and made to eat organic matter," he said.
 He focused on the microbes were already living in the water stored in the balancing reservoir. He thought that if these microbes were bred successfully, they would eat the organic matter in the rainwater, thereby purifying it. The key here was to find the packing medium that would be most appropriate for the microbes in the reservoir. Packing media are pieces of material with complex shapes that help microbes to multiply by providing them a large surface area on which to live. Following repeated tests in collaboration with a water treatment company, Zaitsu found that a fibrous packing medium would be the most suitable, for the microbes living in the No. 1 Balancing Reservoir and also from the perspective of maintainability and operation costs. In this way, he succeeded in purifying the water to below the regulatory limit for organic substances.
 Furthermore, Zaitsu also assembled an apparatus to remove viable bacteria using ultraviolet radiation. As a result, the Kumamoto Factory was able to develop an original rainwater purification system and even obtain a patent for it.
 In 1998, the Kumamoto Factory began operating the system using rainwater stored in the No. 1 Balancing Reservoir. The new system allowed the factory to use up to about 130,000 tons of rainwater per year, significantly more than the most water it ever used in one year since then: 100,000 tons. In the years of the systems construction, the factory managed to reduce its demand for cooling water, partly as a result of changing plant facilities and the types of products it produced. Currently, annual rainwater use ranges between 50,000 and 60,000 tons.
 "Although it appears that we use only half of the system's capacity, this is the maximum because we use rainwater for all of the cooling water used by plant facilities. Rainwater also has five times longer life than groundwater. This is because rainwater contains far fewer minerals than groundwater, which reduces the amount of impurities that become concentrated and deposited in our equipment in the process of using cooling water repeatedly. This means we save an amount of groundwater that is equivalent to five times the amount of rainwater we use as cooling water," Zaitsu said.
 Zaitsu is also considering using rainwater not only as a coolant but also for cutting and a mold release operations. However, in order to use rainwater directly for producing parts and products, repeated tests are necessary to determine whether rust and corrosion issues can be overcome. He says he will move forward with his plans carefully.
 Lastly, to the question of how much profit has been generated by using the rainwater system, Zaitsu replied, "While we’ve managed to minimize costs by using existing equipment, we made a relatively large investment in the introduction of this system. When simply considering costs alone, you find that continuing to use groundwater is actually cheaper. So why did the Kumamoto Factory introduce this system, then? The answer is: to conserve groundwater through our own efforts and to pass on the blessings of Kumamoto’s natural environment to future generations. To that end, we saw the rainwater system as a necessary investment and decided to introduce it. We hope to keep this harmony between the Kumamoto Factory and nature going for many years to come."

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