Sourcebook of Alternative Technologies for Freshwater Augumentation in Africa


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<Sourcebook of Alternative Technologies for Freshwater Augumentation in Africa>

2.2.3 Use Of Natural Plants

Technical Description

The Moringa oleifera is a small tree which grows to about 10 m high in the Sahalien and Sudano-Sahalien zones of Africa. The seeds of this tree can be used as a flocculent aid for water purification. Enough Moringa seeds must be ground in proportion to the quantity of water to be treated. The necessary quantify of powder is mixed with a little bit of water and allowed to stand for a few minutes before use to allow the ground seeds to settle. This water is decanted through a sieve and is mixed with the water to be purified. Once mixed, the vessel holding the water to be treated must not be moved for at least an hour to allow the process to work in an efficient way (Figure 39).

Figure 39. Moringa seed water purification using traditional gourds as treatment vessels.

Extent of Use

Water treatment based on this technology is used in all West African countries. In West and Central Africa, the Moringa oleifera is used most commonly by housewives in the preparation of sauces. The tree grows along water courses and in the plains, and is called by different common names according to the language used in each portion of its range throughout this vast area. However, the use of seeds for water purification is not so well known.

Operation and Maintenance

The Moringa oleifera seed powder must be prepared just before its use. The means of preparing and using the seeds is as follows:

(i) remove the skin of the fruit and trim seeds;

(ii) dry the seeds;

(iii) crush or grind the dried seeds to a powder;

(iv) mix the necessary quantity of the powder with a little water;

(v) decant the water and mix the liquid with the water to be purified;

(vi) mix the water and the liquid rapidly with a stick for at least 5 minutes;

(vii) place the water being treated where it will not be disturbed;

(vii) cover the water container, wait 1 to 2 hours, and collect the purified water.

Rapid Gravity Sand Filtration

Technical Description
Raw water is pumped into a flocculation chamber into which aluminium sulphate is added to aid in coagulation of contaminants. In some cases, electrolytes or other chemicals are also added. The floc is then settled before the water is filtered through a rapid gravity filter. The filter bed must be periodically cleaned by back washing to avoid clogging.

Extent of Use
This technology is used throughout Africa.

Operation and Maintenance
Use of this technology requires pumping units and other chemical dosing units which need periodic inspection and calibration. The sand filter requires periodic back-washing.

Level of Involvement
This technology requires a technically qualified operator.

Costs
Costs are fairly high in comparison with other systems, especially if additional electrolytes are required.

Suitability
The technology is suitable for large urban centres.

Environmental Benefits
The are no known negative impacts associated with properly maintained systems. However, sludge from the flocculation chambers may cause pollution if not properly disposed of.

Advantages
This technology provides high quality water, and is a proven method for large-scale water supply.

Disadvantages
The technology is expensive to operate.

Effectiveness of the Technology
The technology is effective in polishing raw water to produce pathogen-free potable water.

Cultural Acceptability
This is a global technology; no cultural problems have been noted.

Slow Sand Filtration

Technical Description
Raw water is filtered through a sand bed made of uniformly graded sand overlying a gravel bed. Treatment occurs through physical, biological and chemical processes. Some treatment occurs in the "schmutzdekke".

Extent of Use
This technique is widely used in rural areas of Africa.

Operation and Maintenance
Minimal maintenance is required.

Level of Involvement
Use of this technology requires few technical skills.

Costs
Costs of construction and operation are reasonably low.

Suitability
Slow sand filtration is suitable for small settlements.

Environmental Benefits
There are no known negative impacts of using this technology.

Advantages
The technique provides high quality potable water at low cost, without the need for chemicals.

Disadvantages
The filters need regular resanding and periodic removal of the top sand layer for optimal operation.

Effectiveness of the Technology
The technology produces a product water with near zero coliform counts

Cultural Acceptability
This is a global technology and is culturally acceptable.

Level of Involvement

In west and central Africa, making water drinkable by using the Moringa is still in the experimental stages. Both government authorities and the communities are still not heavily involved in using this technology.

Costs

The cost of using this technology is in terms of the time spent in gathering the seeds, preparing them, grinding into powder, and using the powder to purify limited volumes of water. Each family must have several containers, depending on size. For ease of preparation and use of the treated water, a vessel with a tap should be used. A typical installation for using this technology ranges in capital cost from $7 to $10.

Effectiveness of the Technology

This technology eliminates up to 99% of bacteria found in water. A good, full seed will typically purify 5 l of water that is not turbid; two seeds will purify between 2.5 l and 5 l of water that is slightly to moderately turbid; and three seeds will purify 2.5 l of very turbid water.

Suitability

The Moringa can be cultivated, in well drained soils, such as those soils which are suitable for purifying unsafe wastewaters.

Advantages

Moringa-based technologies are simple and are a practical method of water purification. It is an inexpensive technology.

Disadvantages

Moringa seeds are not available throughout the year, which curtails the ability of this technology to perform year round.

Cultural Acceptability

The purification of water using the Moringa is little known in West and Central Africa, but leaves are already eaten by members of most societies.

Information Sources

Contacts

CIEH, B.P. 369, Ouagadougou, Burkina Faso. Tel. 307112. GTZ, Dog Hannarsk Joedureg 1-2, D6236 Eschborn 1 RFA.

Bibliography

Sania, A. and V. Azhasia s.d. Water Purification in Tropical Developing Countries. GTZ, Eschborn.

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