Early years

Japan's modern sewerage system construction started in early Meiji era about 130 years ago, to prevent inundation by urban rainfall and outbreaks of infectious diseases caused by stagnating untreated wastewater. However, it was not defined as a major infrastructure until the revised Sewerage Law was amended in 1958, and the percentage of the population served by the sewerage system did not exceed 6% at that time. Since then, sewerage system construction focused on large cities and developed actively with the objective to improve the urban environment and to contribute to sound urban development and enhancement of public sanitation, as defined by the Law.

Apparition of new water challenges in the 1960s

Until the late 1980s, on-site sanitation, with night soil (or black water) and sludge collection, was the main way to treat wastewater in Japan. Night soil collection was already an entrenched and popular business throughout the country in the Azuchi-Momoyama Era (1573-1603), as it was recycled as a fertilizer for agriculture. Nevertheless, severe water-related issues appeared during the 1960s, when the rapid growth of industry and urbanization caused a substantial increase in water demands, as well as the deterioration of water quality in rivers and other water bodies.

Night soil formerly collected in villages, towns and cities became gradually replaced by chemical fertilizer and almost abandoned for agriculture after 1960. In addition, with the influence of the modern American life style subsequent to the Second World War, a social and cultural demand for a complete separation of human waste and the daily living conditions emerged. With the important concentration of population in large cities and the end of the collection system, night soil became in excess all over Japan. To face this situation, the sanitation-related scientists and engineers in Japan paid great efforts to develop a wide range of new sanitation technologies.

As a key measure to prevent water pollution, the Japanese government actively promoted the construction of night soil treatment facilities throughout the country, as well as sewerage facilities. The revision of the Sewerage Law in 1970 brought new nationwide standards for water quality and a series of subsidize programs supported the construction of night soil facilities. It also encouraged the important technological development associated with the diffusion of sanitation facilities. These series of measures marked an important step for the reduction of water pollution and the environmental protection in Japan.

Rapid expansion of the public sewerage system

From that time, the public sewerage system quickly spread in densely populated urban areas to become the main sanitation system from the late 1980s (to date, it covers more than 70% of the population). Meanwhile, the Japanese decentralized wastewater treatment system called johkasou was diffused in rural areas or in towns with low population density (covering about 20% of the population now). Johkasou is a unique system that was devised and developed in Japan. This compact technology can treat domestic wastewater for individual houses, or group of houses, and discharge a high quality effluent (with BOD effluent below 20 mg/l) to the surrounding water bodies; thus maintaining sufficient water amounts in rivers, and preserving the environment.

Still now, on-site sanitation systems are widely used in Japan, accounting for about 30% of the total sanitation coverage. Night soil collection from vault toilets and sludge from johkasou is regularly conducted through vacuum trucks, in compliance with the Johkasou Law. To date, 1,100 night soil/sludge treatment plants are in operation in Japan, playing an important role in the preservation of water resources. Currently, only 0.2% of the total population is not covered by either on-site or off-site systems. Almost all of the night soil and the human waste receive treatment, and 80% of household wastewater is treated either by the sewerage system or the johkasou system before being returned to the natural environment.

In about 40 years, Japanese sanitation has achieved outstanding results and rapid growth, while developing a tremendous amount of technologies and know-how. For many years, this useful experience and knowledge have been successfully taught and passed on to some countries of the Asia-Pacific through international cooperation, including exchange programs for academia, expert staff training, information sharing in technology and regulations/policies. However, the alarming sanitation conditions observed in emerging nations of the region require further assistance that can be realized through information exchange and knowledge sharing.

Future trends

Japan's trends in the coming years will be to further develop the principles of water, energy and reuse/recycling.

Sanitation can also play an important role in global warming control, an increasing cause of worry in recent years. The use of biomass and natural energies such as solar, hydro and wind power showed that greenhouse gas emissions could be effectively reduced in wastewater treatment, which is a natural lead for the development and application of new technologies.

Advanced wastewater treatment

Advanced treatment has been developed to improve water quality in water bodies where satisfactory result could not be obtained with secondary treatment. Additionally, advanced treatment is applied where treated wastewater is recycled and where wastewater treatment plant's effluent is discharged into areas of drinking water sources. As of March 2005, 277 treatment plants were using advanced treatment, including areas with closed water bodies such as lakes and the three main bays (i.e., Tokyo Bay, Ise Bay, and Osaka Bay). To further promote the installation of advanced treatment, the Sewerage Law was amended in 2005, and from that time includes reduction targets for nitrogen and phosphorous.

The technologies currently utilized in Japan enable the removal of nutrient, odor, color and for high levels of disinfection. In coming years, technologies that provide even higher effluent qualities than currently will be developed and spread.

Wastewater reuse

With the increase of water consumption and the periodic shortage of water observed in some areas of Japan in summer, wastewater reuse is more and more required. It has been actively promoted in recent years for the following purposes:

  • Earthquake/disaster mitigation measures:
    to enable the use of flush toilets after a disaster; to use non-potable water for extinguishing fires;
  • Global warming mitigation measures:
    to utilize the heat of reclaimed wastewater; to use wastewater in the event of droughts and allow more stable quantity and quality of water to avoid shortages; to reduce greenhouse gas emission with a more efficient use of water;
  • Water quality increase of surface water;
  • Improvement of urban amenities;
  • Non-potable urban uses for toilet flushing, train cleaning, and road sprinkling;
  • Agricultural irrigation.

In Fiscal Year 2006 in Japan, 194 million m_ of wastewater have been reused (1.4% of the total amount of treated wastewater) through 286 treatment plants (14% of the total wastewater treatment plants). In the future, more efforts will be made to increase this amount and to provide different qualities of water according to different utilization. Indeed, why using drinking water quality for toilet flushing or car washing?!

Sludge recycling

Currently in Japan, the main focus of treating the huge amounts of wastewater sludge produced is changing from reduction of volume to its conversion to a source of materials and energy. Through treatment process, sludge can become an important source of energy and can be recycled for different purposes. Since the 1990s, there has been great progress in Japan in the utilization of treated sludge as a construction material. Its utilization as a cement material became a dominant practice, particularly since the mid-1990s. Sludge is also utilized as compost for agriculture, after being dewatered and stabilized through fermentation.

The beneficial uses of treated wastewater sludge has increased to over 60%, and the rate of its utilization for farmland and areas of greenery has been rather stable around 14% for many years. While this rate is likely to be maintained in the future, recent technical development facilitates the recovery of phosphorus, which offers new utilization possibilities and is an important resource for agriculture. Anaerobic digestion to recover energy from sludge has also been reconsidered as a measure to control global warming effects. In addition, the development of fuel from sludge or biogas as a raw material for urban gas supply have become a focus of attention as new energy forms that can be substituted for fossil fuel, and applications have already started in Japan. Consequently, beneficial utilization of sludge and sludge treatment has become more connected and in the future, all the sludge treatment will be conducted by taking account of its utilization from the users' viewpoint.

Furthermore, the increased amount of digestion gas obtained from the fermentation of solid waste, vegetation and other organic waste materials will be beneficially utilized. Already, the Public Works Research Institute has been developing element technologies whereby sludge is mixed with grass, wood, and waste material and treated together at wastewater treatment plants as a means of generating energy.

Research and development projects for developing countries

Each country differs in characteristics and needs. As for developing countries, the capital cost and running cost of wastewater facilities, as well as operation and maintenance, can be difficult issues to tackle. To address these, energy and cost-saving technologies with easy operation and maintenance are currently under research and development in Japan, such as the UASB-DHS system from Dr. Harada, Tohoku University. Other technologies, formerly used in Japan, are also considered for international cooperation.

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