IV. Water Resource Management of Kobe City

WASTEWATER TREATMENT SYSTEM

There are two main ways of managing wastewater and stormwater: either in one combined sewage system, or in two separate sewage systems. A combined system requires fewer collection channels, but results in full treatment of essentially clean stormwater. A separate system requires two separate collection schemes, but only wastewater is treated at the sewage treatment plant. Kobe uses a separate system. Other cities, including Tokyo, Osaka, and Nagoya, use a combined system. One particular advantage that Kobe has is that the many steep elevations in the city allow the use of gravity to make it easier to collect stormwater.

The primary purpose of the wastewater treatment and sewage system is the improvement of the living environment, especially the installation of flush toilets. A second important role is flood prevention. This is accomplished primarily by the construction of sewers and sewage pump stations to remove stormwater.

A third important role is to help maintain the quality of the public water supply, by treating wastewater at treatment plants before it returns to the rivers and seas.

A fourth important role is helping manage the effective use of resources. By recycling treated water and incinerated sludge ash, these materials are used again instead of being merely disposed of. Sewage is becoming an important resource in its own right, as continuing technology developments increase its potential applications. Pavement blocks, for example, can be easily made from incinerated sludge ash, and treated water can be used for purposes such as vehicle washing and plant watering.

Sewage systems can also be useful in emergencies, providing water for firefighting in case of disasters such as earthquakes, and protecting the city in times of heavy rains and high tides.

A potential use of the sewage system is as a conduit for optical fibers. These can be installed in sewers and used for effective management of the sewage system and other governmental administrative purposes. Private optical fiber networks could also be routed through the sewage system.

The basic process used in Kobe to treat wastewater is to first begin to separate solids in a settling basin. The wastewater then moves through a first sedimentation basin, a bioreactor, and a final sedimentation basin. Small or dissolved particles which do not easily settle are digested by microorganisms, mainly bacteria. The clear liquid is then directed back to rivers and oceans. Part of the treated water is filtered through fine sand or mixed with ozone for use in the treatment facility or for other reuse purposes.

Sludge from the sedimentation basins is collected and concentrated in a sludge thickening tank, then moved to a sludge digesting tank where fermentation prevents decomposition, with excess gases being routed to a gas tank for burning. The residual sludge is collected in a dehydration facility in the form of a dehydrated cake, which is incinerated at an incineration facility, reducing the cake's volume and stabilizing its quality. Approximately 35 percent of the ashes are ultimately reclaimed for other uses, with the rest disposed of in landfills.

In Kobe, a sewage system was first begun in 1872. (A few sections of the original sewers, now more than 130 years old, are still in use today.) Despite this early start, Kobe was late in introducing modern sewers citywide. In 1951, construction began on a modernized sewage system. In 1958, operation of the Central Treatment Plant started.

The connection of residences to the modern sewage system in Kobe has increased steadily over the years, from 3 percent in 1960 to 98.2 percent in 2002.

Sewerage Systems in Kobe Expansion

With the growth of the modern sewage system in Kobe, there has been a corresponding increase in groundwater quality improvement.

The status of the sewage system in Kobe is as follows:

Sewage treatment plants	Seven (five in the coastal area, and two inland.)
Pump stations	24
Total length of sewers	4,395km
Amount of treated sewage	507,208 cubic meters per day
Annual volume of inciner-ated ashes (dry)	4,560 tons per year.
Population in residences connected to a sewage network	1,482,100

Today, the sewage system is facing different challenges. One is to increase the use of high-level treatments, which purify the wastewater to the fullest extent possible. High-level treatments use microorganisms to treat the wastewater, which is necessary to remove nitrogen, phosphorus and other contributors to eutrophication, a contributor to red tide. Though the number of red tide occurrences has decreased sharply in recent years, they have not been eliminated.

However, there are significant issues regarding high-level treatments, especially regarding who should be burdened with the high costs associated with the treatment. In conventional wastewater treatment environments, those who receive the benefits, or cause the expense, bear those costs. But high-level treatment results in water environment improvement in a wider area, resulting in a more difficult expense assessment issue.

Effective use of space is another means of utilizing the resources of the water treatment system. A neighbourhood park facility has been built over a treatment plant in Tarumi Ward, and another natural park like setting has been created in Nishi Ward.

Hiraiso Lawn Park

Kobe maintains separate accounting systems for sewage services. This business unit is operated as a standalone entity. It costs 172 yen to treat a cubic meter of wastewater. About 60 percent of sewage system revenues come from fees and charges assessed for using the system.

Future targets of improvements in business performance:

1. Reduction in costs by controlling construction investment. A goal of reducing these expenses by 20 percent has been established.

2. Reduction in the cost of supplies. A target of a 5 percent reduction in supply costs has been established.

3. Reduction in personnel expenses, to be accomplished by the use of senior staff, outsourcing efforts and effective staff assignments.

4. Use of the sewage enterprise fund. Funded mainly by apartment complex developers, this fund will be more effectively utilized, for example, by using investment profits from the fund to pay interest expenses.

There are several key characteristics of the water environment in Kobe. First, there are few water resources inside the city, and 75 percent of tap water is supplied from outside the city. There is usually only a small amount of water in rivers and streams. The groundwater is largely a closed system, with little seawater circulation.

This is one reason why water quality control is so important. Sewage has a great influence on the quality of the water environment. In Kobe, the amount of sewage is almost equal to the amount of water supplied. This high recovery rate is a key factor in maintaining the cleanest possible water environment. As a reminder to citizens of this vital resource, in one downtown location part of the sewer system has been left visible at street level, so that people can see this important public utility that is usually out of sight and out of mind.

Editor's Note: This article is a summary of the following lectures and site visits: Lecture on "Population and Water Supply Project of Kobe - History, Current State, and Technical Challenges" by Tetsuo Kijima, Manager of Waterworks Bureau, Kobe City Government. Lecture on "Current State and Challenges of Water Supply Management of Kobe" by Mr. Takeshi Tachikawa, Manager of Waterworks Bureau, Kobe City Government. Lecture on "Current State and Challenges of Sewage Management of Kobe" by Mr. Kyozo Takenaka, Manager of Public Construction Projects Bureau, Kobe City Government. Site visits to Water Purification Plant and Water Quality Examination Center of Kobe and Higashi Water Environment Center of Kobe. Site visit to the Hiyoshi Dam. Lecture on "Environment Issues of Lake Biwa" by Dr. Machiko Nishino and Dr. Yoshihiro Azuma, researchers of the Lake Biwa Research Institute. AUICK takes full editorial responsibility for the contents.