Technologies for improving combined sewer systems
ENTRY DATE: 23.04.2012 | LAST UPDATE: 23.04.2012
CATEGORIES:
- Water Resources
- Improvement of water quality
TECHNOLOGIES MATURITY:
Ready for introduction, to be applied immediately
Technology Owners:
Local governments, private sector companies (environmental equipment), etc.
Needs Address
The need to reduce the impacts of deteriorating quality of public waters (particularly enclosed water bodies, etc.) as a result of climate change, in areas that may face declining sanitation conditions.
Adaptation effects
・Limiting the deterioration of water quality in enclosed water bodies due to the effects of climate change, etc.
・Prevention of deterioration of sanitation conditions and reduction of disease risk due to climate change, etc.
・Improved wastewater treatment capacity to handle extreme events
Overview and Features
・Combined sewer systems, which release wastewater and rainwater into the same sewers, are commonly used in large cities. In recent years, however, rainwater mixed with wastewater is released into public waters when the intercepting sewer capacity is exceeded during rainfall events, leading to concerns about negative impacts on sanitation and ecological impacts where the wastewater is eventually discharged.
・To address these concerns, it is necessary to develop a strategy for each facility. Below are examples of options for each type of facility.
Examples of technology, by type of facility
|
Facility |
Strategy Option |
Technologies Applied |
|
Sewer system (piping) |
Maintenance |
Pipe cleaning, repair/maintenance of flashings/pipes, measures to prevent infiltration |
|
Flow control |
Orifices, gates, expansion gates |
|
|
Optimization of interception system |
Optimization of interception/mixing, reduction of mixing, rainwater outfall integration |
|
|
Optimization of intercepted volume |
Increase intercepted volume |
|
|
Effective use of existing pipes |
Bypass pipes |
|
|
Separated flows |
||
|
Storage / infiltration |
Infiltration |
Infiltration wet wells, infiltration trenches, porous pavement, infiltration wells |
|
Reservoir |
Onsite storage, rainwater capture pond, downstream storage facilities |
|
|
Treatment |
Handling of debris |
Filtration screen, overflow screen during rainfall, traveling screen, oil fence facilities |
|
Solid/liquid separation |
Storm water settling pond, settling with inclined slab, solids-separation vortex equipment |
|
|
Upgrading of primary treatment |
Pressure flotation method, rapid flocculation settling method, rapid filtration method |
|
|
Escalated sewage treatment during wet weather |
Activated sludge sewage treatment during wet weather |
|
|
Disinfection |
Chlorination, etc. |
|
|
Measurement and control systems |
Automatic E. coli detection device |
|
|
Pumping facilities |
Improve capacity of facilities |
Convert settling pond and pump wet well to dry types, use finer screen apertures |
|
Raw water and sewage Sources |
Strategies to deal with sources |
Street cleaning, separating the flow of roof runoff, cleaning of wet wells, control of littering, control of discharge of oily substances |
Source: Compiled from "Improving combined sewer systems: countermeasures Guidelines and Commentary " (2002), Japan Sewage Works Association (in Japanese).
Cost
・A case study for improvements in a model treatment area (serviced area 100 ha, wastewater volume when no rain (daily average): 2000 m3/day) produced the following results:
Proposal 1:
・ Install a rainwater storage pond (3,400 m3 per location (type III), watershed area initial rainfall 3.4 mm)
・ Reduction of debris: Install screens in each storm water outfall chamber (3 locations)
Cost: 7.7 million yen (plus cost of land for storage pond)
Proposal 2:
・Install interception pipe (φ 600 mm, L=500 m)
・Upgrade primary treatment (rapid filtration): 30,000 m3/day
・Reduction of debris: Install screens in each storm water chamber (3 locations)
Project cost estimated at 5.84 million yen.
Source: "Guide for emergency improvement plans for efficient combined sewer systems" (draft), March 2008, Ministry of Land, Infrastructure, Transport and Tourism (in Japanese).
Energy source
Electricity
Ease of maintenance
Management and maintenance technology of each facility in the combined sewer system is required.
Considerations
This technology requires a combined sewer system to already be in place.
Co-benefit, suitability for developing countries
・Improvement of sanitation by proper treatment of domestic wastewater.
・Water quality conservation of rivers and marine areas
Information Resources
・" Improving combined sewer systems: countermeasures Guidelines and Commentary " (2002) apan Sewage Works Association (in Japanese).
・"Guide for emergency improvement plans for efficient combined sewer systems" (draft), March 2008, Ministry of Land, Infrastructure, Transport and Tourism (in Japanese).