Illustrator Hiroki Tsuboi Visits Sumitomo Group Biogas power plant using ume seasoning effluent Sumitomo Heavy Industries Environment
The Minabe-Tanabe area of Wakayama Prefecture is celebrated as the foremost producer of umeboshi, salted and pickled ume plums that are a feature of Japanese cuisine. But a long-standing concern is the rising cost of treating the ume seasoning effluent. Sumitomo Heavy Industries Environment has come to the rescue with its BIOIMPACT high-efficiency anaerobic wastewater treatment system for biogas power generation.
Biogas power plant that uses ume seasoning effluent in rural Kamitonda Town, Wakayama Prefecture. The plant would serve as an emergency power supply for an adjacent clinic in the event of a disaster.
In the novel BIOIMPACT Reactor, highly efficient separation of gas, treated water, and sludge is performed.
We are heading for the biogas power plant at Kamitonda Town in southern Wakayama Prefecture, a 30-minute drive from Nanki-Shirahama Airport. As we approach it, we see large cylindrical tanks looming in the distance. Wakayama Prefecture is famous for ume. It is Japan’s largest producer of umeboshi and other foods featuring processed ume. In the small Minabe-Tanabe rural district, where more than 200 umeboshi producers are clustered, treatment of the ume seasoning effluent has long been an issue. Mr. Shinichi Kogushi, corporate communications manager of Nakata Foods, a leading producer of foods featuring ume, explains the local situation.
“In recent years, rather than the traditional umeboshi seasoned with salt alone, the trend is toward low-sodium riffs on the traditional theme, flavored with honey, dried bonito flakes, etc. In the production of these types of umeboshi, you have to remove a lot of salt while soaking the ume in seasoning liquid. The less salt in the umeboshi, the more seasoning liquid is used. Ume seasoning effluent has sky-high concentrations of salt and sugar. Its biochemical oxygen demand (BOD) concentration* is comparable to that of tonkatsu sauce. Indeed, 26,000-fold dilution is necessary to render the effluent benign for fish. Since the wastewater treatment capacity in the Minabe-Tanabe area cannot cope with all this umeboshi seasoning effluent, we contracted industrial waste treatment companies outside Wakayama Prefecture to deal with it, but the cost of treatment, including transportation costs, has been rising.”
It just so happened that a paper presented by a lecturer at a local technical college caught Mr. Kogushi’s eye. It suggested the possibility of using ume seasoning effluent as an energy source.
“We consulted the local government of Kamitonda Town about the possibility of locally recycling ume seasoning effluent to produce energy for the community. But that proved to be a nonstarter because of high cost of constructing a treatment plant. So, we considered establishing a plant in a joint venture with a local industrial waste treatment company that would collect effluent from local umeboshi producers. We thought it would be a viable new business. So, we asked Sumitomo Heavy Industries Environment to conduct a preliminary assessment prior to construction of a plant.”
Intensive treatment system
Sumitomo Heavy Industries Environment has more than 60 years of experience in planning, design, and fabricating water treatment systems, such as sewage plants and industrial wastewater treatment plants, environmental sanitation facilities, and waste treatment facilities. The decision was taken to adopt Sumitomo Heavy Industries Environment’s proprietary BIOIMPACT high-efficiency anaerobic wastewater treatment system whose track record goes back over 30 years. Following verification at a scaled-down plant, it was concluded that the best solution would be to convert the organic matter in ume seasoning effluent into biogas, generate electricity using the biogas, and sell the electricity under the feed-in-tariff (FIT) program.
Mr. Ryusuke Saito, an engineer with Sumitomo Heavy Industries Environment’s Engineering Department, who was involved in designing the biogas power plant, briefs us on the anaerobic treatment method. “There are basically two biological treatment methods: anaerobic and aerobic. In anaerobic treatment, anaerobic microorganisms, which do not require oxygen, break down organic matter into methane gas, carbon dioxide, and water. Compared to aerobic treatment, in which microorganisms requiring oxygen break down organic matter into carbon dioxide and water, anaerobic treatment offers benefits. The methane gas can be used as an energy source and treatment costs are slashed because no aeration power is required and there is far less sludge,” says Mr. Saito. In other words, anaerobic treatment hits two targets: it reduces the environmental impacts of purifying and discharging ume seasoning effluent and the burden of plant maintenance costs is reduced because the electricity generated using ume seasoning effluent as biomass is sold.
Biogas power plant using ume seasoning effluent
We are guided round the biogas power plant. If you love the distinctive sour aroma of ume, you will love this place with its stacks of containers full of ume seasoning effluent. The effluent is fed into a tank. In a conventional process, the effluent would be fed into an acidification tank in the next step. But at this plant, the high-sugar-content effluent first undergoes alcohol decomposition in the AG-Reactor. Following comprehensive testing, Sumitomo Heavy Industries Environment designed and patented the reactor.
Next, following conversion to acetic acid in the acidification tank, everything is fed into the BIOIMPACT Reactor, the largest vessel. Biogas is recovered from methanogenic granular sludge formed in the reactor. The recovery rate is 98%. After sulfur is removed in the desulfurization tower, the gas is supplied to a gas-powered generator to generate electricity. Meanwhile, following treatment in the BIOIMPACT Reactor, purification of the water is almost completed, except for finishing treatment by aerobic microorganisms to reduce chemical oxygen demand (COD) and suspended solids (SS) to less than a quarter of the values mandated by the prefecture and local fishery cooperatives. When the temperature of the cooling water for the generator’s radiator reaches 70°C, the heat is extracted by a heat exchanger to heat well water for use in the dilution facility. The entire system is designed to minimize waste.
Ume seasoning effluent in 13 containers. Nakata Foods alone produces 103 of effluent per day.
Once the plan for the plant was finalized, Mr. Kogushi couldn’t wait for it to be up and running. He didn’t want to see all that energy-rich ume seasoning effluent go to waste. And once the plant is operating at full tilt, it is expected to generate 5,650kWh of electricity per day, enough for 400 households. Wakayama Prefecture would suffer major disruption if the Nankai Trough earthquake were to occur. In the event of such a calamity, the plant could serve as an emergency power source.
Carbon neutrality initiatives are underway worldwide. It strikes me that what the world needs is systems that don’t just treat waste but convert it into energy. In other words, the extension of “local production for local consumption” to include electricity.
* The amount of oxygen used by microorganisms to break down contaminants in water. The higher the BOD, the higher the contamination level.
Umeboshi as an energy source!?
Editor's note
When we arrived at head office and factory of Nakata Foods, what first caught our eyes was a series of photos and autographs of well-known Olympic athletes on the wall alongside the walkway used by visitors. The company has been providing its umeboshi, salted and pickled plums, as a pick-me-up for Japanese athletes at the summer and winter Olympics since the 2004 Summer Olympics in Athens. Nakata Foods umeboshi was among the snacks enthusiastically consumed by the highly successful and much-loved national curling team during their snack breaks or “mogu mogu time,” which became a buzzword in Japan in 2018. Mogu mogu is Japanese onomatopoeia representing the sound of munching.
Directly managed store of Nakata Foods within the site of its head office and factory
Number(Manga Reportage "Visits to Sumitomo Group")
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