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2.6.2 Subsurface Drainage Technology

In rural areas and in areas with no public sanitary drainage networks, a simple technology is utilized under the Palestinian Authority for the reuse of the liquid domestic wastes. This technology is known as the subsurface drainage technology (sometimes called septic tanks) and can serve one residence, and even several residences if their liquid wastes are collected in a single system.

Technology Description

This technology consists of three components. The first component is a plastic pipeline network that collects the liquid wastes from a residence and conveys it down a natural slope to a separate collection tank outside the residence. The tank is made of reinforced concrete or solid bricks and consists of two or more chambers. Each chamber is separated from the other by a wall that is slightly lower than the tank’s ceiling. Each chamber is connected to the other with plastic pipes (Figure 54-b). The second component consists of the distribution intake that connects the liquid wastes flowing out of the collection tank to the distribution network. The distribution network is the third component, and consists of a network of perforated plastic pipes extending under the soil in special channels. The pipe network is surrounded by a lining of stones (Figure 54-c).

The liquid waste flows from the residence through the plastic pipes to the collection tank. The heavy solid materials settle out in the first chamber. After a period of time, the water in the first chamber rises to the level where it fills it and begins flowing into the second chamber through the pipes installed on top of the wall separating the two chambers. The settling and decay process continues in the second chamber until it is filled. The water then flows through the plastic pipes from the tank to the distribution intake and subsequently to the distribution network. As the water flows through the distribution network, it is drained to the surrounding soil through the perforations in the pipe surfaces and the surrounding stone lining.

The estimated dimensions for a collection tank for an average-sized residence is about 2x2x3 meters, which is a total volume of 12 m³. The required land area for installation of the distribution network and the reuse of the treated water must be at least 80-800 m². The lengths of the plastic pipes in the network must not be less than 15 meters, and can reach up to 40 meters.

Extent of Use

The technology is used on a large scale in rural areas and camps of the occupied areas of Palestine. The Save the Children Foundation has initiated support for the residents by providing them with the technical experience and required construction materials. In turn, the residents have provided the labor, individually or collectively, to construct the system.

Operation and Maintenance

There are no mechanical components, or specific operational problems, in the system. The treatment process begins as soon as the residence is connected to the collection tank.

Figure 54. Sub-surface drainage technology

The use of this technology began 12 years ago, and no significant operation problems have been recorded during this period. Nevertheless, a resident may need to clean the solid materials out of the first chamber approximately every 10 years, or sooner if unpleasant odors begin emitting from it.

Level of Involvement

This technology has received very strong attention from residents, especially in rural areas.

Costs

The total cost of the sub-surface drainage system for an average size residence is about US$ 250, without any foreign financial support or cooperative participation of residents. Half the cost is for the connection pipes and the distribution network, while the other half is for the tank and water distribution intake. If the resident already has the basic construction materials, or constructs the sytem himself, the cost is reduced to about US$ 100.

Effectiveness of the Technology

This technology has proven to be effective in treating sanitary drainage water, and for facilitating sub-surface water reuse for agricultural purposes.

Suitability

This technology is suitable for the environment in occupied Palestine, especially in the absence of sanitary drainage networks. In general, the system is suitable for most soils, except in regions with clayey soils which can cause drainage problems.

Advantages

The advantages of this technology are as follows:

• The technology provides significant quantities of water in a region suffering from water scarcity;
• It is inexpensive, and does not present any significant health concerns;
• It is easy to install and operate, and requires a minimum of maintenance;
• It prevents direct contact between the treated sanitary drainage water and plants;
• It contributes to groundwater recharge.

Disadvantages

The major disadvantage with this technology is that it may lead to groundwater contamination.

Cultural Acceptance

This technology is accepted by both urban and rural residents.

Further Development of the Technology

Steps for further development of this technology would include the following:

• Construction of prefabricated tanks in different sizes, for different residence sizes and their varying quantities of liquid wastes;
• Development of ways to prevent shallow groundwater contamination;
• Study of the changes in water quality that take place through the drainage system, from the collection tank through the end of the distribution network;
<>Determination of the quantities and quality of the water infiltrating into the soil, and determining the appropriate agricultural crops for irrigation purposes with the water.

Information Sources

Contacts

Marawan Haddad
Faculty of Enginering, Najah National University
P.O. Box: 7
Nablos, Palestine
Tel: 972-9-2381115
Fax: 972-9-2385680

Save the Children Foundation
Nablos Branch - Najah Street
Nablos, Palestine

References

Haddad, M. 1999. Palestine Country Report, Project for the Preparation of the Source Book for Alternative Technologies for Freshwater Augmentation in West Asia Region. Internal Technical Report, ACSAD, Damascus, Syria.

 

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