Updated: July 2002

1. Outline of the system

Recently, such problems as eutrofication in closed waters and pollution in public water systems have cropped up. As a measure against this environmental issue, there is an increasing need for high-performance sewage treatment systems. In response to this need, by participation in Bio Focus WT National Project, NKK has developed Bio-Tube, a unique sewage treatment which provides a new engineering concepts in the field of waste water treatments through its use. This is a carrier application technology which allows high-efficiency, low-cost and space-saving water treatment system through immobilization of microbes in high concentrations.

2. Features

Bio-Tube is a cylindrical hollow solid mainly made of polypropylene, outside diameter of 4 mm by inside diameter of 3 mm by length of 5 mm, with fine projections and depressions on its surfaces. It has the following features.

- Fine projections and depressions on the surfaces facilitate holding microbes.
- Slowly growing Bacteria such as nitrifying bacteria, can be held to the carrier.
- Its large specific surface area allows microbe population in large quantities.
- Bio-Tube spreads evenly in water due to its specific gravity being near that of water.
- Because there is no need to store
- Bio-Tube under humid conditions, storage is easy.

Before attachment of microbes

After attachment of microbes

3. Performance

Effects of the Bio-Tube System

- Permits operations under high BOD loading and high nitrogen loading conditions.
- Requires less space and minimum capacity of aeration tanks.
- Achieves stable treatment performances.
- Is easy to maintain.
- Allows an advanced treatment under high load conditions using existing aeration tanks.

4. Fields of Application and Target Waste

(1) Bio-Tube System Type I (BOD removal system)
BOD and SS can be removed with high efficiency by a combination of carrier immersion type aeration tank and upflow sand filtration basin. The use of Bio-Tube is capable of reducing a retention time of treatment process in about a half comparable to conventional activated sludge processes.
(2) Bio-Tube System Type II (High load-ready system)
Even if throughput and pollution loads are increased, the stable quality of treated water can be maintained by making minor modifications to existing aeration tanks.
(3) Bio-Tube System Type III(Nitrogen removal & treatment system)
Both nitrification and denitrification rates are increased to remove BOD and nitrogen by immersing Bio-Tube in aerobic tanks of the circulation type nitrification and denitrification processes. The use of Bio-Tube allows treatment in a retention time of 6 to 8 hours, similar retention times as in conventional activated sludge processes.
(4) Bio-Tube System Type IV (Simultaneous nitrogen and phosphorous removal & treatment system)
Both nitrification and denitrification rates are increased to remove BOD, nitrogen, and phosphorus by immersing Bio-Tube in aerobic tanks in anaerobic, anoxic, and aerobic processes.
The use of Bio-Tube allows treatment in a retention time of 7 to 10 hours, leading to a considerable reduction in reactor volume comparable to conventional activated sludge processes.