Capillary Purification Systems Co., Ltd., a consulting firm specializing in the installation of unique wastewater treatment technologies utilizing soil microorganisms—known as soil purification methods—has been building a strong track record in small-scale sewage treatment facilities and agricultural village wastewater treatment facilities.

Capillary Purification Systems Co., Ltd., a consulting firm specializing in the installation of unique wastewater treatment technologies utilizing soil microorganisms—known as soil purification methods—has been building a strong track record in small-scale sewage treatment facilities and agricultural village wastewater treatment facilities. The company is also drawing attention as a rare example of private-sector technology being adopted for public works projects. Furthermore, as a technology that aligns with natural ecosystems, the company is expected to expand into Asia in the future. ● Facilities Covered by Sewerage Fees As of the end of fiscal year 2005, Japan’s sewerage coverage rate was 69.3% (population using sewerage / total population), but in municipalities with fewer than 50,000 residents, it remained at just 39.3%. It is inherently impractical to uniformly expand sewerage systems—which were originally designed for urban areas—across the entire country. To make matters worse, local governments are already facing severe budget cuts. The soil purification method developed by the Capillary Purification System has thrown a wrench into this situation surrounding sewage systems. “It is said that the construction cost of a sewage system exceeds 1.5 million yen per resident. For a population of 10,000, that amounts to 15 billion yen. This is not a sum that a municipality of 10,000 people can afford. So, should we install small septic tanks in every household? Assuming four people per household, that would require 2,500 units for a population of 10,000. Each unit costs 1,000–1,500 yen per month in electricity, and when you add in other maintenance costs, the burden on each household would be more than double that of sewerage fees. ‘Is this really a realistic solution?’ asks Hiroko Kimura, the company’s representative director. The Sakashita West Treatment Center in Aizubangata Town, Fukushima Prefecture, which employs soil purification technology, began operations in fiscal year 1993 with a planned capacity of 1,400 m³. Due to increases in connection rates and treatment volume, the daily inflow exceeded 400 m³ by fiscal year 1999. The facility has since turned a profit after covering maintenance costs and is now able to repay its bonds. The sewerage fee is 140 yen per cubic meter. Furthermore, in the case of the Chuo Purification Center in Chiran Town, Kagoshima Prefecture (serving 4,000 people with a capacity of 2,400 m³), which began partial operation in fiscal year 2001, the sewerage fee is 90 yen per square meter, and the facility turned a profit as early as the following year. ● Key Features The Soil-Covered Soil Purification Method is a unique water treatment technology that utilizes soil microorganisms to decompose pollutants. When adopted for municipal sewage systems, it is known as the Soil-Covered Inter-Gravel Contact Oxidation Method; for agricultural village wastewater treatment facilities, it is known as the Niimi System (certified by the Minister of Land, Infrastructure, Transport and Tourism). This is because the governing agencies and relevant laws differ for each application. In both cases, the basic process flow consists of sedimentation and separation, contact aeration, sedimentation and contact filtration, disinfection, and discharge. The first key feature is that the treatment facility is covered with soil. This reduces odors and prevents the spread of splashes and pathogens from the treatment tanks. The covered wastewater treatment plant becomes a green space covered with plants such as grass. Furthermore, when it rains, microorganisms from the covering soil fall into the treatment tanks, helping to maintain a healthy environment within them. The second feature is the contact aeration tank, which uses filter media onto which aerobic microorganisms have been attached. After sludge is stored for one day in the sedimentation tank, it is purified over the course of one day in the contact aeration tank. In aeration tanks that utilize suspended organisms, such as those in the activated sludge process, adjustments by specialized technicians are necessary to ensure uniformity within the tank. Furthermore, such aeration tanks are essentially just boxes, resulting in a short retention time. In contrast, the soil remediation method divides the tank into long channels. As the water flows through these channels, organic matter is decomposed by multiple types of microorganisms, resulting in high purification capacity and stable treated water. Furthermore, almost no adjustment of the tank is required, and maintenance consists only of removing sludge a few times a year. The third feature is that it is an energy-efficient system requiring minimal mechanical equipment. A major factor in keeping construction costs low for soil purification facilities is that the soil cover eliminates the need for a treatment plant roof and equipment for deodorization and defoaming. ● Local Governments Making the Decision to Adopt It As of April 2006, the system has been adopted at 68 facilities nationwide. However, when the company was founded in 1980, “We never imagined we’d end up in the sewerage sector. People used to say that private-sector technology wouldn’t be adopted for public works projects like sewerage,” recalls Mr. Kimura. Initially, the company handled septic tanks and miscellaneous wastewater treatment for public facilities using the Niimi Trench, which channels wastewater through soil containing microorganisms. The Niimi Trench was a simple structure that involved digging trenches around a building and utilizing the purification capacity of the soil ecosystem to treat wastewater without the use of power. In 1983, the company established the Niimi System as a soil-covered septic tank and obtained general certification for facilities serving up to 500 people. “To obtain certification for even larger scales, we were required to provide data on microbial species and purification capacity, which demanded significant research funds and time,” said Mr. Kimura. Currently, the Niimi System has obtained certification for communities of up to 4,000 people. A major turning point came in 1990 with the establishment of the Central Purification Center in Shimukappu Village, Hokkaido, which adopted the soil purification method as a sewerage facility. The Ministry of Construction (at the time) refused to provide subsidies for the soil purification method, citing the lack of precedents. In response, Shimukappu Village requested subsidies only for the pipelines, and as a result, the facility was approved for subsidies as a model project. A treatment facility capable of handling 1,000 people and 460 cubic meters—which would have cost 500 million yen using conventional sewage treatment methods—was constructed for 130 million yen using the soil purification method. Following the designation of three additional sites as model facilities, in 1991, the Ministry of Construction announced a policy stating that, if there was strong demand from local governments, the Soil Purification Act would be eligible for subsidies as a sewerage project. The Takago Purification Center in Ogawa Village, Nagano Prefecture, which began operations in fiscal year 1995, became the first example in which the Japan Sewerage Works Agency adopted the Soil Purification Act, thereby establishing its position as a sewerage technology. “Funding programs are supposed to improve the lives of the people. If they impose excessive or unnecessary burdens on local governments and residents, I don’t see the point of the funding,” Mr. Kimura points out. He adds, “The soil purification method is not only low-cost but also creates facilities that residents appreciate.” Many local governments hold an annual “Sewer Festival.” It is not uncommon to see residents enjoying a picnic on the grass covering the sewage treatment tanks. In April 2000, municipalities equipped with Soil Purification Act facilities established the National Association of Municipalities for the Soil Purification Act. While the association aims to facilitate the exchange of information regarding maintenance and management, it also demonstrates the municipalities’ determination to take the lead in advancing sewerage projects—projects that had previously been carried out under national guidance—on their own. Meanwhile, in response to cuts in public works budgets, the Ministry of Land, Infrastructure, Transport and Tourism is moving to revise the previous uniform national standards. ■ Amid this trend, Mr. Kimura has proposed the “Slim Sewerage Project.” Having gained confidence through past achievements—that “the soil purification method allows for development in a short time and at low cost, with construction costs recouped through sewerage fees”—Mr. Kimura states, “It is best if residents and project operators adopt this as a technology to solve local environmental problems.” Going forward, he plans to “propose converting existing treatment plants, which incur enormous maintenance costs, to the soil purification method.” Efforts to expand into Asia are also underway. The soil remediation method has already been adopted at over 100 sites in South Korea and is attracting attention in China as well. Given its high effectiveness in improving river environments within treatment areas, the soil remediation method is sure to be in demand in Asian countries where water quality deterioration is becoming increasingly apparent.