Medium and larger urban communities can have cost-effective chemical-free or chemical-minimized sewage treatment using oxidation ditch sewage systems. These operate as stand-alone biological treatment units and are in operation across the Asia-Pacific region.
WRG evaluated numerous variants developed to recommend and supply Oxidation Ditch (or single stage nitrification) sewage treatment systems in association with technology partners Environmental Holdings and AWA-Envirotech. The processes involved in oxidation ditches have dramatic benefits over larger footprint systems on an area and volume treated basis.
As indicated below, oxidation ditch systems are installed worldwide, often in close proximity to residential and commercial premises. The systems are now increasingly being used for whole districts of major cities, such as in China and Malaysia, to take the full sewage load of these areas up to 250,000 PE. Oxidation Ditch systems are also very effective in Industrial Wastewater Applications
Traditional sewage systems are static, large footprint and energy intensive. WRG's preferred sewage treatment is smaller scale, biologically aerobic, low energy input, minimal odour, mostly chemical-free with fast reaction times suitable for reuse applications.
Process Overview
The Oxidation Ditch is a highly efficient aeration system using very low speed surface aerators. Aerators are mounted at watercourse channels in a racetrack configuration to provide complex mixing in the aeration zones. Plug flow exists in the channels between the aerators.
Flow velocity of 0.3m/second is maintained in the channels due to the pumping action of the aerators. Surface aerators applied in the conventional systems are generally designed to have a power intensity of 0.7 to 1.2 HP per 1,000 cubic ft, compared to an Oxidation Ditch which are typically designed at 0.4 HP per 1,000 cubic ft. This results in both better aeration for BOD reduction, etc, as well as very large power cost savings over conventional sewage systems. Flexibility can be achieved by adjustable immersion of aerators, alternating operation of aerators, or a variable rpm of the aerator. Equipment life of the aerator could easily exceed 30 years.
Low speed surface aerators have the following power ratings 5.5kW, 7.5kW, 11kW, 15kW, 18.5kW, 22kW, 30kW, 37kW, 45kW, 55kW, 75kW, 90kW, 110kW, 132kW and 160kW. Australian designed impellers are supplied ranging from 1.3m to 4.0m in diameter.
Achievable Results
Oxidation Ditch Urban Sewage Treatment benefits include:
95-99% BOD removal efficiency
Over 90% Nitrogen removal by denitrification
Over 50% elimination of Phosphorius compounds
Over 95% Phosphorius removal if Fe salts added
Lowest excess and stable sludge production
Effective and safe ammonia removal
Low to minimal odour emissions
Able to handle major hydraulic and biological shock loadings
Maximum operational simplicity
Limited sludge processing and treatment required
Minimal operational control required
Minimization of construction cost
Potential integration with tertiary wastewater treatment
Site Applications
Site applications suited for Oxidation Ditch sewage treatment include:
Towns EP 1000 +
Cities and suburban districts
Condominiums
High rise apartment blocks
Ecological resorts
Island urban networks
Larger military bases
Industrial applications
Key Specifications
| System |
SRT Loading |
%BOD Removal |
Aerator Detention Hours |
Nitrifi-cation |
Recirculated Underflow Solids Rate |
| Extended Aeration |
>30 |
90%+ |
16-24 |
Yes |
100-300 |
| Conventional |
4-8 |
90-95% |
4-8 |
Possible |
30-100 |
| High Rate |
2-4 |
85-90% |
2-4 |
No |
30-100 |
| Modified Aeration |
<1 |
60-75% |
0.5-2 |
No |
10-30 |
| Contact Stabilization |
3-10 |
85-95% |
- |
Possible |
25-75 |
| Contact |
- |
85-95% |
1.0-3.0 |
No |
50-100 |
| Stabilization |
- |
- |
3.0-6.0 |
Possible |
- |
| Oxidation Ditch |
10-15 |
95%+ |
6-12 |
Yes |
30-100 |
Reference Sites
There are numerous Oxidation Ditch sewage treatment units operating 24 hours/day in the Asia Pacific region, including:
| EP |
Client |
Location |
Application |
| 230,000 |
Liao Cheng Municipality |
Shandong China |
Total City |
| 10,000 |
Sunrise |
Kuala Lumpur |
High Rise Suburb |
| 9,500 |
JBT Kramat |
Kuala Lumpur |
Low Rise Suburb |
| 5,000 |
Taman Kinrara |
Selangor Malaysia |
Town |
| 3,400 |
Samudra Council |
Selangor Malaysia |
Town |
Technical Information Downloads
Technical and issue documentation PDF files can be downloaded from this page by clicking on the relevant hyperlink.
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Oxidation Ditch (439Kb)
