A visit to Kobe City’s eastern sludge plant, Tobu, on 7 June served two purposes. It provided the participants with another example of the complex machinery that is Kobe’s effective sanitation system. In addition, it was the first step in Pingyi Sun’s action plan for Weihai. That city has a problem with its sludge, the heavy residue that settles out from waste water. Weihai produces 100,000 tons of sludge annually from its 30 million tons of sewage. Worse, this sludge is 80% water; the volume is too great for the landfill and the water leaches out into the soils and groundwater. A close examination of the Kobe system could provide Weihai with a valuable model for managing its sludge problem. 

The plant is located on 2 hectares site on the northern sore of Rokko Island. This is the second of Kobe’s man-made islands from its famous “mountains to the sea” project. That project, begun in 1965, cut land from the tops of the Rokko Mountains and dumped the fill into the sea to make one then two artificial islands, Port Island and Rokko Island. This relieved the Kobe shipping bottleneck and helped promote Japan’s rapid economic development from 1960 on. It also expanded the city in a creative manner as the cut mountain tops became sites for new towns, suburbs for apartments and houses, universities and industrial and research parks.

Typical of Japan’s sanitation infrastructure, the sludge plant is housed in an attractive building set in a lovely park with trees and flowers. Its business is dealing with dirt, but it looks like a super clean and green operation.

The splendor of Tobu Sludge Center

The plant began operations in 1986. Its task is to manage the 600 tons of sludge per day, which comes from part of Kobe’s 550,000 cubic meters of wastewater treated daily. The sludge is dried, extracting some 150 tons of evaporated water, then incinerated at 850 degrees Celsius. The 200 tons of sludge incinerated in each of 3 furnaces produces 12 tons of ash. Some of this goes to the landfill, some goes to a private company to make paving bricks and asphalt extender; some is also turned into fertilizer for the city’s parks and flower beds. The gas produced in the incineration process is cooled, cleaned, and deodorized before being vented as non- polluting air from the facility’s stack. A system one third this size would reduce Weihai’s 100,000 tons of sludge to a mere 6,000 tons. Moreover some of the ash from the sludge could be turned into fertilizer and paving materials, further reducing the pressure on its land fill.

A variety of energy-saving measures are built into this system. For example, the heat from the incinerator is further used to produce steam for drying some of the sludge and for preventing emissions of white smoke. Air for the combustion is used to send odors from the sludge pit to a preheater before being sent to the incinerator. This reduces fuel and deodorizing expenses.

There is more effective conservation going on Rokko Island in addition to the effective sludge management. Waste water from the Higashinada waste treatment plant on the mainland opposite Rokko Island is piped to the island for further cleaning and refinement. This water is then used to flush toilets, water the trees and flowers, and fill the picturesque streams that run along the road and paths on the island. For this “grey” water, households pay 120 yen per cubic meter while business establishments pay 200 yen. This is one of many of Kobe’s efforts to conserve water and manage its overall water environment more effectively. It provides Weihai with many valuable lessons.

The layout of Tobu Sludge Center