Updated: July 2002

1. Advantages

1) Removal of soluble organic substance which is difficult to remove with active sludge, is possible.
2) Treatment of wastewater whose level of contamination is low, is possible.
3) Easiness of operation control and automatic control.
4) Small installation area is required.
5) Resistance against fluctuations of quality and quantity of water, and steady availability of treated water of good quality.

2. Physical Properties

There are two types of active carbon: granular carbon (shredded carbon and globular carbon) and powdery carbon. The former is more widely applied to the treatment of wastewater. The active carbon has macropores of 10^-2-10^-4 and micropores of 10^-5-10^-7mm and the substance which is diffused into the macropores, will be adsorbed to the surface of the micropores. The surface area is 1,000-1,500m², which is large enough and appropriate to be used as adsorbent. The main properties are as follows;

True specific gravity: 1.9-2.1
Special surface area: 500-1,500 m²/g
Bulk specific gravity: 0.3-0.5
Mean grain diameter: 1.1-1.5 mm

3. Adsorption Methods

There are following methods concerning the adsorption of active carbon.
Type of Adsorption Tower Direction of Water Flow

Fixed bed : Downflow
Moving bed : Upflow
Multistage fluid bed : Upflow
Contact adsorption : --

4. Re-generation

The re-generation methods of active carbon are as follows; (1) low-temperature regeneration method by overheated steam of 120ºC-150ºC, (2) high-temperature heat re-generation method with heat of 500ºC-900ºC, using the multi-stage furnace, rotary kiln, fluid bed furnace, etc., (3) the chemical method. Nevertheless, in the case of the re-generation of active carbon used in the wastewater treatment, the high-temperature heat re-generation method is generally used. In this method, the re-generation is done by way of the following process;
1) Drying step
Drying of active carbon sent from the dehydrator, at the temperature of 30ºC-100ºC.
2) Baking step
Evaporation, gasification and baking of adsorbed substance at the temperature of 100ºC-800ºC.
3) Activating step
Activation of substances, already decomposed and oxidized in the baking step, under the existence of steam.

5. Vertical & Moving Bed Type Re-generating Furnace

The above-mentioned process can be performed effectively by using the vertical and moving bed type regenerating furnace; this is the furnace used to re-generate the shredded carbon and granular carbon.
The re-generation of active carbon is done inside a vertical tube. This re-generating tube is composed of a double heat-proof steel tube, and the active carbon shifts from upward to downward directions in the ring between the internal tube and external tube. In the meantime, the activated carbon is heated from the outside by more than one burner, installed inside the furnace, and each step of drying, baking and activation is done continuously. The structure of the furnace is conceived in such a way that the gas generated in the course of each process, will enter the furnace through an opening provided to the external tube and then, the complete combustion of gas will take place. The steam required for the activation is fed from the internal tube, and will accelerate the reaction of water gas in the active carbon bed. This furnace has the following advantages, compared with other types of re-generating furnace;
1) The loss of re-generating furnace.
2) There is no danger of secondary pollution.
3) The maintenance can be easily done.
4) Being light-weight and small-sized, it will not take much space.
5) The thermal efficiency in the furnace is high.
6) The operating range is wide.