Sewage Works in Osaka, Japan
Respond to New Demands through Advanced-Technology R & D
(1) Developed Sewerage Systems through Advanced-Technology R&D (R&D : Research and Development)
The city of Osaka has been conducting various kinds of researches of sewerage technology in order to meet the diversified social needs such as reduction of environmental load and treatment cost, etc. As a result, advanced sewerage technologies and facilities have been developed.
Sewerage system occupies an important place in the water and material circulation in urban area. The roles of sewerage system are expected in a wide range of fields such as treatment of wastewater and discharge of stormwater as well as conservation of water environment and water circulation, ensuring secure urban life and creation of an eco-friendly and recycling society.
Furthermore, the active promotion of existing technological improvement and development of advanced treatment technology is required to achieve the measures effectively meeting social needs.
The city of Osaka has been implementing the joint research with private companies which have useful technologies, as well as promoting original research and development of sewerage technologies.
Example of Multi-story Wastewater Treatment Facilities
Effective use of land in sewerage facilities
The city of Osaka has been required to increase its capacity of sewerage facilities by effective use of limited space in order to correspond to increase of the amount of sewage triggered by rapid urbanization.
We have been especially surveying multi-story sewerage facility and developed two-story and three-story sewage treatment facilities for primary and final settling tanks.
The three-story primary and final settling tanks are applied first in the world.
Furthermore, "The deep reaction tank" having a depth of 10m, namely about two times deeper than the former tank was also developed by the city of Osaka.
Development of those space-saving sewerage facilities enabled effective use of limited land in sewerage facility premises.
In addition, various measures for effective land use of sewerage facilities are taken such as construction of multi-story sewerage facility whose upper part is rapid sand filtration tanks and lower part is stormwater reservoir, and so on.
Development of Thermophilic / High Concentration Anaerobic Digestion System
The basic concept of the sludge treatment process in Osaka city is as follows :
- Separate gravity thickening of primary and excess sludge
- Two-stage thickening of excess sludge
(Aiming effective sludge thickening method, primary sludge and excess sludge are thickened by gravity separately, and excess sludge, which is difficult to be thickened, is further thickened by mechanical thickener such as using a centrifugal thickener, etc).
- Thermophilic and high concentration anaerobic digestion
- Centrifugal dehydration
Thermophilic and high concentration anaerobic digestion is a stable and effective sludge digestion method originally developed by the city of Osaka in order to solve sludge treatment problems caused by the change of sludge condition due to the lifestyle change and urban development.
Sewage sludge digestion has been adopted in Osaka city to reduce solid waste disposal from sewage treatment plants. And thermophilic digestion process can contribute not only to reduce heating energy consumption, but also to increase quantity of digestion gas generation dramatically. The quantity of the methane gas produced is more than that we need for the thermopilic process. We applied digestion gas power generation system to make good use of increased digestion gas and reduction of greenhouse gas.
A Power Generation System Utilizing Digestion Gas
Digestion gas, which mainly consists of methane, is useful as a clean energy that can save fossil fuel consumption.
In Nakahama Sewage Treatment Plant, digestion gas is used for power generating system. Generated electricity covers some portion of the electricity consumption in the plant. Furthermore, exhaust heat produced from the digestion gas engine is utilized to heat digestion tanks for effective energy use.
In Ebie Sewage Treatment Plant, digestion gas is used for fuel cell power generation.
A Power Generation System Utilizing Digestion Gas
Fuel cell power generation facility in Ebie Sewage Treatment Plan
Automatic Monitoring System of Industrial Wastewater Quality
We used to monitor illicit discharge from industries to sewerage system by conducting on-site inspection by human work.
The city of Osaka has developed the "Automatic Monitoring System of Industrial Wastewater Quality" which enables continuous monitoring by multiple sensors and automatic water samplers to secure 24-hour monitoring of industrial wastewater.
Automatic Monitoring System has interactive functions. It can collect data from the multiple sensors that measure pH, electric conductivity, dissolved oxygen, oxidation-reduction potential and water temperature. It sends the data to the central computer using the mobile data communication service so that we can grasp the real-time water quality data. At the same time, it also can transmit signal to order automatic water samplers to sample.
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An automatic water sampler |
An automatic water quality measuring instrument |
Sedimentation process using inclined plate settlers
By use of a lot of inclined plates installed in settling tanks, effective space for settling is increased so that settling efficiency can be improved. This treatment process is effective especially when sewage treatment plants accept wastewater exceeding their capacity during heavy rain event, when some portion of the stormwater which contains pollutant from sediment of sewerage facilities is discharged to public water bodies without treatment.
As plate settlers sedimentation process has high treatment efficiency, it only requires about 1/3 space of conventional sedimentation facility.
Combination of "Sedimentation process using inclined plate settlers" and "Wet Weather Wastewater Treatment Method" would reduce pollutant discharge load during wet weather.
The settling tanks with plate settlers for wet weather have been operated since FY2003 at Ebie Sewage Treatment Plant.
Installation Diagram of Inclined Plate Settlers
Step inflow type Two-stage Nitrification-denitrification process with carrier addition
The quality of the receiving water body has been improved thanks to sewer service development in Osaka City, however, there are still some rivers that do not comply with water environmental quality standards. Red tides are also observed more than 20 times a year in Osaka Bay, a closed water area. Aiming at creation of higher quality of water environment, the city of Osaka has successfully developed an advanced wastewater treatment system that can remove nitrogen effectively.
In this method, ammonia nitrogen is effectively nitrified by nitrification bacteria which are kept on floating carrier. Floating carrier is useful to keep nitrification bacteria which breed slower than other bacteria decomposing organic substances.
Osaka City also developed a high efficiency aeration and mixing system (I-shape aeration system) and a screen type separators for floating carrier to apply to nitrification-denitrification process in 10 m depth reaction tanks originally developed in Osaka City.
These facilities were partially installed in Konohana Sewage Treatment Plant, and have been used as a pilot plant since FY2003.
Installation Diagram of I-shape aeration system
Installation Diagram of Screen Type of Carrier separator
Principle of Screen Type of Carrier separator
Nitrogen Removal Process by Step Inflow
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