Updated: July 2002

1. Purpose

With the help of hydraulic pressure, the ultra-depth aeration tank of about 100 meters high treats BOD/COD in the wastewater at a higher rate and a higher load, because the dissolved oxygen of higher density activates the microorganisms efficiently. This process, one of the floating-type biological processing technologies, is capable of handling higher BOD load and coping with varying loads especially because the wastewater discharged by the paper-manufacturing industry is large in volume and relatively lower in density. The installation area of the equipment can be smaller; hence, the process is popular among the paper-manufacturing industries.

2. Performance and Characteristics

(Examples for paper-manufacturing)
BOD removal rate: >90% (215mg/l -> 10mg/l)
COD removal rate: >80% (260mg/l -> 37mg/l)
BOD volumetric load: 3.7kg/(m³d)
Retention time: 1h

3. Features

1) Space saving:
While the aeration tank of the standard activated sludge process is of flat type, the deep shaft process tank is installed in a deep vertical bore in the ground, the area required for installation is approximately 1/20 of that for the conventional type.
2) Energy saving:
Compared with the standard activated sludge process, the oxygen utilization factor is higher anywhere from 5 to 9 times; hence, the air blown in can be in the order of 1/6 through 1/8. This tends to lower the running cost.
3) Effective for high density wastewater:
Due to higher density of dissolved oxygen and higher oxygen utilization factor, the process is capable of handling high density wastewater and sewage effectively.
4) Less sludge:
With ample supply of oxygen, the microorganisms are in very much active state; hence, the treatment capacity is large and the volume of sludge produced tends to be small.
5) Smooth restarting:
Restarting of the system can be completed smoothly only in one day's time even after about 10 days' system shutdown.
6) Other favorable features:
- Capability to cope with load variation
- Operation not being influenced by the weather conditions
- Less odor generation

4. Principles

The deep shaft process carries out the biochemical treatment of wastewater efficiently by dissolving oxygen in the air quickly into wastewater. The shaft having a bore of from 1m to 6m, as shown in the illustration, is installed vertical in the ground as deep as 50m to 150m, and is divided into two sections by a cylindrical perpendicular wall: down-coming and up-rising section.
The inflow is introduced to the top, and it goes down toward the shaft bottom as it is mixed with the circulating liquid in the shaft.
The air introduced into the down-coming section travels toward the bottom mixed with the circulating liquid which circulates in the shaft at the rate of 1 to 2 m/s, and by the time the air reaches the shaft bottom the most of it is dissolved into the liquid due to higher hydraulic pressure. Thus, the deep shaft process, being capable of producing dissolved oxygen of higher density, completes the biological treatment rapidly and positively.

5. Flowsheet

6. Applications

Pulppaperpaper-product manufacturing industry
Food industry
Chemical industry
Sewage industry
Office buildings (flushing water recycling system)