A technology to help stagnant waters 'breathe' again

JStories ー The first things we tend to think of when we hear the term “global warming” are melting glaciers and rising sea levels. However, global warming is also a major cause of water pollution. As water temperatures rise, phytoplankton multiply. This causes abnormal growth in organisms such as blue-green algae and reduces the amount of oxygen in the water. Fish and other algae suffocate while foul odors and toxic substances spread, destroying the aquatic environment.

In recent years, global warming has caused a chain reaction of worsening water quality and deteriorating ecosystems. This has been observed in oceans, rivers and lakes not just in Japan, but around the world. The presence of blue-green algae has even been confirmed in Russia's Lake Baikal, regarded as one of the world’s clearest lakes.

One way to halt this deterioration in water quality and restore aquatic environments is an artificial process called “Lake Biwa deep breathing.” It mimics a natural phenomenon in Lake Biwa, Japan’s largest freshwater lake, located just northeast of Kyoto. During the winter, cold air and wind cause the cold water near the surface of Lake Biwa to mix with the warmer water at the bottom, naturally equalizing oxygen levels and water temperature. This purification phenomenon is known as “complete turnover” or “lake overturn” in English, but can also occur in the ocean due to wave movement caused by large storms.

In the past, one method to promote complete overturn and revitalize stagnant water has been to blow air into the water. However, it is expensive and the large size of the equipment required makes it unsuitable for rivers and other shallow bodies of water. Chemicals can also be used for quick results, but there are concerns over long-term residual effects on water quality and ecosystems.

A number of startups are working on technologies that can promote natural purification through so-called Lake Biwa deep breathing. One is Ebismarine, based in the southern Japanese city of Nagasaki. Specializing in environmental technology, the company has obtained patents in 25 countries and is working to clean up water in various regions.

Ryoji Terai, chairman of Ebismarine and president of its parent company, Ebistrade, explains that its core technology is the “Jet Streamer.” This device achieves more efficient and cost-effective water circulation by using water instead of air. 

“This technology improves water quality throughout the entire water column, from the surface to the bottom, by moving water with water itself, and without using chemical agents,” says Terai.

The cost to install the Jet Streamer in a dam is 50 million to 100 million yen, but this is just around one-third that of conventional devices. Due to its hollow structure, floating garbage won’t get trapped in the device, reducing the need for maintenance. It is mainly made from fiber-reinforced plastic, which combines low weight with high strength and durability. Once installed the system remains operational for over 10 years.

Since the Jet Streamer is smaller and lighter than conventional devices, it is easy to relocate or remove and can also be installed in shallow locations such as rivers. This makes it suitable for temporary seasonal projects, such as during summer months when water quality tends to deteriorate. The company also sells ultrasonic devices and ozone generators, as well as optional extras that offer flexible solutions for different situations, including blue-green algae conditions, water depths, and varying terrain.

According to Terai, the company’s Jet Streamer has already been installed in various locations, from Akita Prefecture in Japan’s north to Okinawa Prefecture in the south. It has been used for jellyfish control at sea, dealing with red tide and blue tide algae blooms, in dams, lakes and marshes, in fish farms, and for water quality improvement at plants. Inquiries have also been received from overseas, including Olympic venues and countries in Asia.

In 2024, the company partnered with Nagasaki Prefecture on demonstration experiments to control red tides using the Jet Streamer, while full-scale operational use of the device in the prefecture is scheduled for this summer. Red tide has caused widespread damage in Nagasaki, including the loss of around 530,000 farmed fish at an estimated cost of 1.5 billion yen. Because of this, the local fisheries industry has high hopes for the technology.

The company is also working on a device that uses air instead of water; or, as it puts it, “moving air with air.” This was jointly developed with the Tokyo Metropolitan Sewerage Service Corp. and is already being used in sewer construction.

“We are ‘flow experts,’” says Terai. Our mission is to stir up stagnant things and revitalize them.” 

Nagasaki Prefecture is particularly prone to stagnant water, surrounded as it is with mountains, sea and many bays. The local economy has also stagnated in recent years, with the prefecture suffering from a shrinking population compounded by what was Japan’s third-highest outward migration in 2023.

“Water, air, the economy… they all cause problems when they stagnate,” says Terai. “We want to make them flow, make them move, and revitalize. There are many places in Japan and overseas that need our technology.”

Ultimately, he says, his company’s goal is to not only revitalize Nagasaki’s environment, but its economy, too.

Translated by Tony McNicol

Edited by Mark Goldsmith

Top photo: Photo courtesy of Ebismarine (Collage by JStories)

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