Updated: July 2002

1. Purpose

The process is intended to treat the high-concentration organic sludge at high efficiency within the digestion tank, and further to dry the sludge and to heat the digestion tank at the same time by using the digestion gas generated through the double effect of energy.
The concentrated organic sludge is supplied to the digestion tank as heated sludge by making it contact with the flash-dried exhaust gas by the dehumidifying tower as shown in the figure.
The dehydrated digestion sludge is used to produce the dried sludge by the flash drier, using the heating air of which heat was recovered from the digestion gas incineration furnace, as its heat source.
Since the dried exhaust gas turns to be dehumidified cool air as soon as the sludge is heated by the steam contained in the exhaust gas, it is not necessary to execute the deodorization treatment by using it finally as combustion air.

2. Performance and Characteristics

Organic ratio of raw sludge -------------- 60-90%
Sludge concentration --------------------- 1-5%
Sludge digestion ratio --------------------- 50-60%
Moisture content of dehydrated sludge ---- 70-85%
Moisture content of dried sludge ---------- 10-40%

3. Characteristic

It is possible to treat the digested sludge as dried sludge without using any combustion improver such as heavy oil, etc. within the process to treat the high-concentration organic sludge by using the anaerobic digestion method.
The system will not require any heating unit such as boiler, etc. or large-capacity gas tank, to maintain the desired digestion tank temperature.
Since the pre-digested sludge can be subjected to heating treatment under the aerobic condition, the enhanced digestion efficiency can be ensured.
It is also possible to design the system to an energy-saving and simplified type, as the blast air generating furnace (used for drying) can be commonly used for dried exhaust gas de-odoring furnace and incineration furnace.

4. Principle

The digestion sludge is dried by using the combustion heat of digestion gas which was generated through methane fermentation of organic sludge, and the digestion tank is heated by using the steam contained in the dried exhaust gas. It becomes possible to ensure the double effect of energy by executing the methane fermentation, combustion, drying and dehumidification independently.

5. Flowsheet

6. Application Field/Object

- Sewage disposal plant
- Waste treatment industry
- Food manufacturing industry

7. Practical Application Examples

- SAGA municipal Waste Water treatment plant
- HAMAMATSU municipal central sewage treatment center
- MIYAZAKI municipal OYODO treatment plant
- CHICHIBU municipal central sewage treatment center