Mr. Michitada Sugahara
Manager, Environmental Conservation Guidance Division
Environmental Bureau, Kobe City Government

Kobe’s physical location gives it many advantages in its water regime, but poses special challenges as well. Reflecting the sharp rise of the mountains, the sea bed plunges deeply beneath the water to give the city a fine natural deep sea port.

Kobe has few natural underground aquifers.  Virtually all of its water comes from its rivers, a small mountain reservoir and lake, and most by a long pipe line from Lake Biwa, some 50 miles to the east.  The population growth has added heavy human and animal wastes to the water system. In 1970 then Mayor Miyazaki pushed through a major expansion of the sewage system to serve the entire population. By 1990 this was largely complete, replacing the extensive use of septic tanks, whose effluent polluted the rivers and the sea side. Now the city has an extensive series of monitoring stations in the sea, streams and lakes measuring Biological and Chemical Oxygen Demand (BOD and COD¹). The extension of the sewage system and greatly reduced BOD levels in the rivers and brought them to national standards. 

¹ This is the amount of oxygen (in mg/liter) required to break down and neutralize biological and chemical wastes. The higher the level, the more polluted the water. Low levels (e.g. 0.1mg/l) imply high cleanliness standards.

Chemical oxygen demands are another thing. The discharge of chemicals increases the COD levels, in part by encouraging plankton blooms that sometimes bring the COD levels above the desired standards in the reservoir and the sea.  A number of interesting remedial measures are being organized by the city. Much effort is being given to organizing the public to assist in cleaning the rivers.  Educational campaigns also increase the public awareness and help to curtail pollution. Domestic effluent is at this time the major source of COD, 53% vs 32% from industrial sources.  Bathroom wastes, 19% and laundry wastes 9% constitute the other major sources. The sea alongside the city’s most heavily populated wards has the highest levels of COD from these household effluents. An extensive poster and educational campaign informs the public of the weight of pollution from normal household effluents. One clever poster shows the number of bath tubs of water (300 liters) that must be added to a specific effluent to clean it sufficiently for fish to live.  This shows that the water left over after washing rice of half a cooker (2 liters) requires 4 bath tubs of water (1200 liters) to clean the effluent. One glass of milk requires 9 bath tubs; 30ml of cooking oil requires 330 bath tubs of water, while a tablespoon of soy sauce requires only 1.5 bath tubs.  Creative posters such as these have proven highly effective in motivating children and housewives to reduce effluents.

Information to enhance public awareness (Source: Domestic effluent treatment measures in Hyogo Prefecture)

Another innovative procedure seeks to clean the sea shore by transplanting seaweed onto the gentle slopes of the two artificial islands built by Kobe, Port Island and Rokko Island, in the period after 1965. This was a highly successful project to increase port facilities and greatly contributed to Japan’s rapid economic development after 1960. As a byproduct, the under water sides of the islands did not plunge steeply into the sea, but were formed as a gentle gradient lined with huge concrete crosses. Sea weed has been successfully propagated among these blocks, where the water is sufficiently shallow to permit sunlight to penetrate and nourish the weeds.  The growing sea weed pumps fresh oxygen into the waters. This increase in dissolved oxygen speeds the decomposition of chemical and biological pollutants.
Finally, an incredible pearl oyster project offers an opportunity to clean the Hyogo canal of pollutants while also providing a valuable product. Kobe is a major center of pearl processing, but the oysters are not propagated in Kobe’s seas waters.  It has been felt that oysters need colder, clean water with high salinity to produce oysters. An experiment hung 100 oysters in the Hyogo canal for a growing season; 44 produced pearls of high commercial quality. Announcing this success in a public meeting, city officials asked if any citizens group would like to take over the project. The chairperson of Hyogo Ward elementary school Parent Teachers Association volunteered and now the project is in the hands of the newly formed “Hyogo Canal Pearl Oyster Project.”  

This will draw students, teachers and parents into a project that can produce many benefits: a cleaner canal and commercial pearl oysters.

Kobe city officials and voluntary citizens groups have thus worked together to meet the challenge of sustainable development. They have found technically proficient and highly creative ways to work together to keep their water environment clean and to build for themselves a city where they can enjoy the natural environment.