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"Membrane Bioreactor" is an activated sludge treatment system that was jointly developed by the Hitachi Plant Technologies, Ltd. and the Japan Sewage Works Agency. By combination of the activated sludge treatment with immersed flat membrane modules, this new system can maintain the activated sludge concentration at a high-level in the reaction tank without use of a sedimentation tank for separation of liquids mixed with the activated sludge. As the results, yield of the treated water at a higher quality then ever before, as well as space saving and reduced operation costs are realized. Since sludge control in a sedimentation tank is eliminated, this treatment system has a feature of easier maintenance.
Features
Space saving
- As the membrane separates solids and liquids, no sedimentation tank is required.
- Due to the shorter treatment time, the system boasts a more compact design.
- Thicknering tank is not required since excess sludge is in high concentration and can be dehydrated directly.
Easy maintenance
- The system has a simple, flat membrane structure whereby impurities are difficult to twine around.
- Easy maintenance and remote monitoring (*)are possible, since the sludge settling control is not required.
- By employment of elements with a large membrane area as modules, easy installation, inspection and replacement are facilitated.
* The remote monitoring system (as a part of the net work support)provided at Hitachi Plant Technologies's Service Station ear monitor the operation status and output an alarm in the event of an emergency.
Low cost
- The system has a simple, compact structure with low initial cost.
- The system generates less excess sludge, which enables the reduction of treatment expenses.
High-quality treated water
- Such advanced treatment as phosphorous and nitrogen removal is performed for six hours.
- The MF membrane (with a pore size of 0.4 μm) is used for filtration, and thereby of coliform bacteria can be completely removed.
- The treated water can be reused for landscape maintenance.
High reliability
- The membrane element is a sturdy, integral structure receiving resin treatment.
Energy saving
- Membrane modules are installed in two-step so that the air for membrane cleaning surface can be utilized more efficiently.
Treatment conditions and main membrane specifications
| Object for treatment | SS, BOD, N, P, and bacteria | |
|---|---|---|
| Biological treatment conditions | Retention time | 6h |
| MLSS | 8,000 to 20,000 mg/l | |
| Membrane specifications | Model | Immersed flat MF membrane |
| Material | Organic high polymer | |
| Pore size | 0.4μm | |
| Membrane area | 20 m2/element | |
Example of water quality data
| Water quality item | Influent | Treated water |
|---|---|---|
| BOD (mg/ l) | 193 | 1.0 |
| COD (mg/ l) | 124 | 7.5 |
| SS (mg/ l) | 250 | < 0.4 |
| T-N (mg/ l) | 38 | 5.7 |
| T-P (mg/ l) | 7.8 | 0.3 |
| Coliform bacteria(numbers /ml) | 3.7 X 105 | Not detected |
Function and Structure
The "Hitachi Membrane Type Sewage Treatment System" employs membrane modules that integrate multi-number of membrane elements, two-stage of which is arranged in the aerobic tank.
The sewage is separated through suction and filtration, so that the filtrated water directly becomes treated water.
Air is supplied from the air diffuser installed on the bottom of the aerobic tank to prevent sludge from adhering to the membrane surface. Thus, the system can perform stable treatment without getting clogged.
Flow of BOD/nitrogen simultaneous treatment system