Features
3 Advanced wastewater treatment system using two-stage anaerobic filter and soil trench technology employed overseas
Yuzuru KIMOCHI

Water Environment Group, Center for
Environmental Sciences in Saitama

Introduction
The soil purification method of sewage has excellent features, such as low construction cost, low energy consumption, and simple operation management. A site or land area for the creation of such facility is easily secured. The system is expected to be applied in countries and regions where stable source of electric power is not readily provided and higher technology is not a feasible option. The two-stage (multi-stages) anaerobic filter and soil trench technology introduces the capacity of a purification system to remove nitrogen from sewage and other wastewater. It is anticipated as sewage disposal technology brought eutrophication prevention into view.

1. Purification flow of the two-stage (multi-stages) anaerobic filter and soil trench technology
This treatment system is designed as one set of an anaerobic filter bed tank and a soil trench. According to targeted treated water quality, it can be created in a combination of two sets, three sets, etc. Anaerobic reaction progresses inside the anaerobic filter bed tank. On the other hand, aerobic reaction advances in the soil trench portion. By proper merging of the two reactions, sewage can be purified without using the complicated control system. As an example, the treatment flow of wastewaters from households using the two-stage system and the rough water quality in each processing stages are shown in Fig. 1.
Three fifths of the amount of sewage from the raw water supply pump flows into the anaerobic filter bed tank-1. Then, decomposition and settling of foreign substances start. Subsequently, the sewage streams into the soil trench-1, where the processes of organic oxidization and nitrification reaction proceed. Afterward, the sewage moves to the anaerobic filter bed tank-2, in which denitrification reaction (process of nitrogen elimination) happens. The denitrification reaction of organic matters on the remaining amount of sewage from the raw water supply pump tank advances as carbon source and nitrogen is removed. Finally, in the soil trench-2, the oxidation of residual organic matters and nitric oxidization are conducted. The treated water is then released. Organic matters and nitrogen can be efficiently removed biologically with the aforementioned technology. Phosphorus, on the other hand, is mainly removed by the physicochemical function like soil adsorption.

Fig. 1Purification flow of the two-stage anaerobic filter and soil trench technology

Fig. 1Purification flow of the two-stage anaerobic filter and soil trench technology

 

2. Features of the two-stage anaerobic filter and soil trench technology
The main characteristics of this treatment system are described as follows.
1) It is an excellent sewage purification method based on a target wastewater. The whole purification reaction is slow. However, effective and stable treatment ability is obtained by combining and optimizing the system according to a treatment target (water quality).
2) It is an energy-saving and costless system. The required materials are soil and gravel, and plastic pipes only. In addition, the operation system which does not require electric power is also feasible. The initial and running costs can be controlled at a low cost.
3) The maintenance of the facilities is easy. Various control equipments and medical agents are fundamentally unnecessary. Moreover, higher technical training and skills in maintenance of the facilities are not essential.
In addition to the mentioned advantages of the system, the effective utilization of headroom of facilities, the regeneration of used soil to vacant and productive lands or farmlands, and the cultivation of groundwater are excellent benefits, as well.

3. Deployment of technology on developing countries
The appropriate application of the technology on sewage treatment system depends according to particular conditions of the areas and countries including climate, etc. in developing countries.
The sewage treatment system utilizing soil is put into practical use in Asian countries, especially in China based on certain circumstances. For example, in China, an anaerobic filter bed and a soil trench system are adopted as treatment of wastewater effluent from student accommodations, dining halls, etc. on the campus of universities. The trench part in Fig. 3 is built using the construction materials illustrated in Fig. 2. The student accommodation buildings are visible at the back. The pipes for the sewage inflow are laid underground into front ditches. Fig. 4 shows the completed structure of the sewage treatment system. Similar cover soil is placed on top of the constructed facilities. The system is installed underground between buildings. Areas such as vacant and productive lands, parking lot for bicycles, etc. are often used effectively. Maintenance becomes easy by prohibiting the erection of buildings above the treatment facilities. The university utilizes the treated water for watering vacant lots, in car washing, etc. Reuse of treated water is an efficient way to conserve water resources. In addition, neither advanced construction technology nor large construction machines are used for the creation of this treatment system. Only manual operation is necessary to effect function of the facility. This feature is indeed an advantage for practical expansion of the system in other places.

Fig.2 Construction materials used in the two-stage anaerobic filter and soil 
trench technology

Fig.2 Construction materials used in the two-stage anaerobic filter
and soil trench technology

Fig.3 Construction process of the two-stage anaerobic filter and soil trench 
technology

Fig.3 Construction process of the two-stage anaerobic filter and
soil trench technology

Fig.4 Completed structure of the two-stage anaerobic filter and soil trench 
technology

Fig.4 Completed structure of the two-stage anaerobic filter and
soil trench technology

4. Ripple effect of the treatment system
The main ripple effects of this treatment system are described as follows.
1) Conservation of water resources for high-quality and safe drinking water supply
The treated water circulates to water resources through groundwater, etc for potential source of drinking water. Thus, it is possible to ensure high-quality and safe drinking water. The improvement in the quality of life of the residents is expected from the standpoint of sanitation. The incidence of disease resulting from consumption of polluted drinking water can be lessened; thus, reduction of medical expenses is also anticipated.
2) Economic effect accompanying preservation of good industrial water
In industries consuming water in large quantities, good service water can be guaranteed by improving the environment of water resources using the treatment facility. Pretreatment process is simple. Lower production cost can be projected.
3) Protection of the ecosystem specifically water environment
The quality of water in lakes, rivers, and other bodies of water could be destroyed by inflow of effluent from households and industrial establishments. Consequently, chemical and biological reactions like eutrophication will result in imbalance of the ecosystems. The application of the treatment system can produce a profound effect on the maintenance of a healthier ecosystem.
 


before
2 Trench system using composite soil for advanced treatment of municipal wastewater
top of contents next
4 Application of multi-soil-layering method in wastewater treatment