Masanori Fujita
1. Evolution of the sewer
Sewerage systems started to accept human waste besides rainwaterand domestic wastewater. Initially a combined sewer system was used. After
wastewater from toilets and industry was allowed, the hygienic status ofurban areas improved but water bodies such as rivers and water channels inurban areas became polluted. Because the sewer system did not include
facilities to treat collected sewage, but carried and directly discharged
sewage into water bodies in urban areas. Pollution of water bodies caused
pollution of water resources, which threatened people’s lives in urban areas.
2. Development of sewage treatment technology
Construction of new sewer systems accelerated pollution of water
bodies in urban areas and resulted in malfunction of water circulation
systems. The demand for sewage treatment increased to stop river pollution
and various kinds of physicochemical and biological treatment processes
were proposed.
A report which was publicized by E. Ardern and W.T.Lockett in 1914
described that sewage is mixed with activated sludge. Then, the mixed
solution is aerated for a short period of time. This produced clean treatedwater. The activated sludge process had been modified and upgraded and avariety of activated sludge processes were proposed. From the research, it
was found that having a deeper aeration tank led to some advantages suchas smaller land requirements and lower energy consumption.
3. Water circulation using sewerage systems
Many cities in Japan faced water shortages because of increasingwater demand due to expanding urban areas and the pursuit of acomfortable life. Treated effluent from sewage treatment plants is a goodwater resource to meet the big demand for parks, biotopes, waterways(artificial streams and rivers) and so on in cities. It can be said that thewater circulation system was established again in urban areas by theconcept of recycling of treated effluent (wastewater recycling.)
To meet water quality requirements when recycling treated effluent
in cities, new reclamation technologies were developed for advanced
treatment of effluent. For instance, they are a membrane bioreactor, arapid-sand filter, ozone oxidation, membrane filtration and so on.

4. Sewerage systems in a sustainable society
At present, they are focused on easing global warming. CO2 emission
should be decreased to stop the global warming. Sewerage systems consume
much electricity and petroleum even for maintenance of treatment plants.
Some plants in Osaka City constructed power generation facilities usingdigester gas (biogas), which has a composition of about 65% methane and
35% CO2 after removing hydrogen sulfide. On the other hand, Kobe City uses
biogas for automobile fuel after raising the methane concentration to about
90%. Suzu City, Ishikawa constructed new biogas plants receiving five kindsof organic wastes such as sewage sludge, sludge from community plants,
night soil, sludge from personal septic tanks and organic waste from several
food processing factories. Biogas in Suzu City is used for steam generation towarm a biogas plant.
5. Summary and future scope
The sewer was a key facility of water circulation in urban areas, whichremoved both rainwater and domestic wastewater in early days. But thesewers did not accept any human waste until 1815. The City of London
permitted toilet wastewater to be discharged into sewers in 1815. Since then,river water was polluted by the sewage discharged from sewers. After acentury, the sewer regained again a key position of water circulation inurban areas by the diffusion of sewage treatment technology. High water
quality standards were then proposed for both safety of life andenvironmental preservation. Eventually, sewage treatment technology waspromoted. In the modern age, environment-friendly sewerage systems
should be pursued to stop the global warming. Energy savings and resource
recycling technology are important design factors. Low cost technology forthe management of sewer and treatment system should be developed torespond to advanced society.
In the future, sewerage systems should also accept kitchen garbage
and pursue more effective material and energy production throughinnovative technology to support the convenient life of advanced living inurban towers. It should not be forgotten to look at reconstruction or renewalof sewerage systems. Finally, it is important to consider that all componentsof sewage should be recovered and recycled to produce effective materials
and/or to generate energy with appropriate and affordable technology insewage treatment processes.