History of Water Pollution Control in Shimane Prefecture - 1999 to 2020s

History of Water Pollution Control in Shimane Prefecture - 1999 to 2020s

In Shimane Prefecture, water pollution control measures have been implemented since the 1990s. 1999 was a time when domestic wastewater was considered a major source of pollution, and its impact on rivers and lakes was becoming increasingly serious. At that time, the sewage system penetration rate in the prefecture was only at the 50% level, and many communities needed to install household septic tanks. The prefecture introduced a subsidy program for the installation of septic tanks, which resulted in a 20% increase in the installation rate over the previous year. In addition, awareness-raising activities and environmental education programs were developed for residents, and awareness of water quality conservation was raised in local communities.

The 2000s
In the 2000s, improvement of water quality in major lakes and marshes, particularly Lake Shinji and the Nakaumi Sea, was promoted as an important issue. During this period, nitrogen and phosphorus from agriculture were regarded as the main causes of water pollution, and stricter fertilizer management and the introduction of organic farming methods became widespread. In 2005, the Lake Shinji-Nakaumi Basin Water Environment Improvement Plan was formulated to protect the water quality of Lake Shinji, and efforts were made to reduce pollution sources throughout the basin. Sewerage system development has also expanded, with the coverage rate in urban areas reaching over 70%, and wastewater treatment capacity has improved.

In 2008, the monitoring system for proper treatment of industrial wastewater was strengthened to ensure that companies comply with wastewater discharge standards. In particular, Shimane Chemical Industry, which has a plant in the prefecture, introduced the latest wastewater treatment technology and achieved a reduction in phosphorus concentration in wastewater of more than 50% compared to previous levels.

The 2010s
In the 2010s, the sewage system penetration rate further increased, reaching a prefecture-wide average of approximately 75% in 2015. During this period, water quality preservation in rural areas emerged as a new issue, and subsidies for the installation of household septic tanks were expanded. In addition, while water quality in Lake Shinji was improving, the occurrence of blue-green algae (cyanobacteria) during the summer months was seen as a problem, and research was conducted to control this problem.

In 2018, the biofilter technology developed by Shimane Ecotech, Inc. attracted attention, and household wastewater treatment utilizing this technology was introduced on a trial basis. This has improved purification capabilities in rural areas and has been highly praised by local residents. Environmental education has also been emphasized, and classes on water quality conservation have been introduced at elementary and junior high schools in the prefecture.

The 2020s
By the 2020s, sewerage system coverage has reached approximately 80%, and water pollution in urban areas has improved significantly. In Lake Shinji, total phosphorus concentrations have decreased to about 0.05 mg/L, and transparency has improved compared to the 1990s. At the same time, reduction of nitrogen and phosphorus from agricultural sources continues to be an issue, and fertilizer management and organic farming methods are being further promoted.

In addition, as a corporate initiative, Eco-Earth Co., Ltd. has developed nitrogen removal technology, which is being introduced both within and outside the prefecture. In addition, with the introduction of "green infrastructure" technology supported by the Ministry of the Environment, a natural purification project using wetland restoration and vegetation strips is being implemented.

Activities involving local residents have also been expanded, and in 2022, a "Water Quality Conservation Forum" was held with the participation of approximately 30,000 people. This has raised awareness of water quality improvement throughout the community and strengthened efforts to involve schools and community organizations.

However, issues such as groundwater contamination and pollution of small rivers still remain, and long-term efforts are required for improvement, especially in unimproved areas. Continued public and private sector efforts are needed.

Sources
- Shimane Prefecture's official website "Water Environment Conservation Plan
- Ministry of the Environment "Green Infrastructure Technology Guidelines
- Eco Earth Corporation, official source
- Shimane Shimbun, archive of local news articles
- Lake Shinji Basin Water Environment Research Report