|Sourcebook of Alternative Technologies for Freshwater Augmentation in Africa (International Environmental Technology Centre - United Nations Environment Programme, 1998, 182 p.)|
|Part B - Technology profiles|
|2. Domestic water supply|
|2.2 Water quality improvement technologies|
Many countries have experienced groundwater quality problems due to high levels of iron in groundwaters. In most cases, these high levels of iron are due to the composition of the bedrock and soils (such as lateritic soils), although, in some cases, high iron concentrations can be caused by the corrosion of the metallic iron pipes within the abstraction or distribution systems.
This technology is designed to make iron-rich groundwaters potable, using a simple and low cost technique. The “Iron Removal Unit” (Figure 38) is composed of an aeration channel (at its head), from which aerated water drops into a rectangular settling basin. The particles of ferric oxide flocculate and settle at the bottom of the settling basin, creating a deposit of iron mud. At five to ten centimetres from its bottom, clarified water from the settling basin is removed to an adsorption basin containing two layers of gravel: the first layer of gravel is usually a 45 cm deep layer of 1.5 to 2.0 cm sized gravel; the second layer of gravel is usually a 25 cm deep layer of 2.5 to 5.0 cm sized gravel. Water flows over a weir at the outlet of the adsorption basin to the sand filtration basin. The sand filter is constructed using a 40 cm thick layer of 0.2 to 5.0 cm sized gravel at its bottom, topped by a 20 cm thick layer of 0.2 to 4.0 mm sized sand. The filtered water is collected by a pipe and distributed to the users.
The various basins that comprise this system have a different direction of the flow in the various basins: in the settling basin, flow is from top to bottom; in the adsorption basin, flow is from bottom to top; and in the filtration basin, flow is again from top to bottom.
Extent of Use
A number of water points in Burkina Faso and Mali are equipped with this type of iron removal unit.
Operation and Maintenance
Users must be trained in the maintenance of the unit. However, once this training has been completed, the unit is very easy to operate and maintain. When people begin pumping, the unit operates continuously without further intervention, except for routine cleaning of the basins to remove accumulated particulates and the back-washing of the sand filter. This technology provides good quality water from otherwise saline water sources.
Level of involvement
Technical assistance is necessary during the construction. Once the system is built and the local people trained for the maintenance and operation, there is no external involvement.
This is a low cost technology. Typical costs in Mali and Burkina Faso range from $250 to $300 per unit.
Effectiveness of the Technology
Studies have shown that there is a considerable decrease in the iron level in the treated water provided by this technology. Based on these studies, the efficiency of iron removal averages between 90% and 96%.
The technique is most suitable in regions with lateritic soils where the high level of iron often results in the abandonment of handpumps by users.
The technology uses local materials and labour to install and operate the unit. It is simple to operate, and requires no chemicals except for those necessary to disinfect the unit after each cleaning. Use of the unit can rehabilitate what would otherwise be abandoned water sources.
If not cleaned periodically, the system may become blocked with the iron floe.
This technology is culturally acceptable in areas where it is used.
Centre Regional Pour l'Eau Potable et l'Assainissement a Faible Cout (CREPA), 03 BP 7112 Ouagadougou 03, Burkina Faso. Tel (226) 310359/60, Fax: (226) 310361.
CREPA 1992. Construction, Operation and Maintenance Manual of an Iron Removal Unit. Centre Regional Pour l'Eau Potable et l'Assainissement a Faible Cout, Ouagadougou.