Cover Image
close this bookSourcebook of Alternative Technologies for Freshwater Augmentation in Africa (International Environmental Technology Centre - United Nations Environment Programme, 1998, 182 p.)
close this folderPart B - Technology profiles
close this folder2. Domestic water supply
View the document(introduction...)
Open this folder and view contents2.1 Fresh water augmentation technologies
Open this folder and view contents2.2 Water quality improvement technologies
Open this folder and view contents2.3 Wastewater treatment technology and reuse
Open this folder and view contents2.4 Water conservation

(introduction...)

Technologies for the augmentation of domestic water supply systems are varied, starting with simple ones at the household level and ranging to more complex ones at the municipal level. Despite the existence of these technologies, access to domestic water supplies remains a problem for a majority of communities in Africa. The major reasons for this situation are the scarcity of water sources which can be attributed to a number of factors including population and industrial growth, increased agricultural activity, the destruction of catchment areas, the deterioration of the socio-economic and political environment, and changes in global climatic conditions, among others. All these factors have created a situation of water limitation. As a remedy to this situation, there is need to maximize the efficiency of use of existing freshwater resources, and to augment existing supplies, by using appropriate, cost effective and environmentally-friendly technologies. These technologies are classified in the broad categories of water harvesting, water quality upgrading, water conservation and water recycling and reuse.

Water conveyance technologies have not been covered in detail as these are not considered as technologies for freshwater augmentation, but, rather, they are a necessary component in the transfer of water from areas of water abundance to areas of water shortage. Hand pumps, and, indeed, other pumping systems, are regarded as water conveyance systems and, therefore, are not discussed in detail. However, some unique, traditionally African methods of water conveyance are mentioned in this section.

2.1.1 Protected springs

Technical Description

There are three elements which comprise a spring catchment installation (Figure 27); namely, a) the “effective” catchment, consisting of a perforated pipe within a trench or dry walled channel (stone package), b) a supply pipe leading to an inspection chamber, and c) an inspection chamber, which consists of an entry basin for receiving the spring water and an operation chamber which helps to control water quantity and quality. Sometimes it can also serve as a sedimentation basin, and, in such cases, may be called silt trap.


Figure 27. Typical spring protection box (WHO, 1992).

Construction should be done during the peak of dry season in order to identify and use the most reliable springs. Nevertheless, spring protection structures have to be designed with overflow pipes so that they can function during peak flows during the rainy season. Usually, the excavation around the spring, necessary for construction of the catchment, is started from the point where the groundwater emerges. Once that excavation is completed, the construction of the other system components starts. There are two parts; preparation of a permeable construction into which the source waters enter, and a dam which prevents the water from bypassing the catchment or reservoir. The dam, or barrage, is constructed opposite to the point of entry of the water into the catchment. It has to direct the source waters into the supply pipe, which conveys the water to the inspection chamber. The barrage has to be built into the impermeable layer, as well as into both side walls, to prevent the water from bypassing the system. The foundation of the barrage is cast into the excavation directly against the ground in order to create a tight seal with the ground. The barrage is then constructed, of either concrete or stone masonry, on top of the foundation. The height of the dam should be positioned lower than the level of the top of the water bearing layer. Difficulties may arise when the source waters have to be bypassed during construction of the foundation. (The flow should never be obstructed!) Usually a temporary dam is constructed of clay behind the excavation, and water is diverted with a temporary pipe or syphoned by a tube.

The permeable construction consists usually of a drain in the dry-stone masonry or of perforated pipes. The cross-section of this catchment drain should be sufficient to ensure that the maximum yield of the spring can be drained off without obstructing the natural spring flow. The drain has to be sloped at 1% to 2%. In the case of a solid substrate, no flooring is normally provided, but, for sandy ground, a dry pavement is needed. The velocity of water should be limited by providing additional catchment drains, considering the maximum flows to be expected during rainy season. Around the drains, a sand and gravel filter should be built up with gravel. The purpose of this filter package is to support the water bearing layer and prevent the fine particles that often comprise this layer from being washed out into the protection structure, resulting in the subsequent collapse of the water-bearing layer. A watertight cover, in the form of a 5 to 10 cm concrete cap, should be placed on top of the drains and the gravel filter. This cover needs to extend 20 cm into the slopes on all sides of the structure. Surface water reaching this cover should be drained off to minimise the potential for groundwater contamination.

Extent of Use

This technology is extensively used for projects in Africa. In Malawi, huge, gravity-fed, piped water schemes have been built, tapping spring water. Likewise, in Lesotho, a number of villages are supplied this way.

Operation and Maintenance

The operation and maintenance of spring protection structures is simple. They require few skills to construct and manage, making them suitable for management by user communities. Where steep drops are encountered (such as in the Lesotho Highlands), good structural designs are required to cater to the increased pressures built up in the supply pipes.

Maintenance activities may include protection of the catchment area from potential contamination, periodic maintenance of the filter package, and cleaning the spring area of leaves and other terrestrial debris. Maintenance is carried out by controlling human and animal activities around the spring, repairing the perimeter fence, and repairing the surface water drainage system. It is also necessary to control of the growth of trees around the spring to prevent roots from causing piping to occur in the sand and gravel filter beds and/or breaching the impervious seals around the reservoir and dam. Periodic testing of the water for bacterial contamination is also recommended.

Level of Involvement

Local input of skills and materials from the beneficiary community is often needed to implement this technology. Technical support may be needed from government, NGOs, and other implementing agencies in the conduct of hydrogeological investigations, structure design, and construction. These activities require the inputs of technically-qualified staff, which depends on the size and nature of the scheme.

Costs

Spring protection is an inexpensive in comparison to the development of a conventional point source. The cost of the protection structure, itself, is largely a material cost (cement, pipes). However added costs may be incurred in the form of costs associated with the delivery mechanisms, which are dependant upon the length of piping, the number of storage reservoirs, and/or the number of pressure break tanks needed.

Effectiveness of the Technology

Springs have been used by local communities as a source of water supply for many years. Their relatively good quality water, and generally very low operation and maintenance costs, coupled with the ease of community management, make them quite effective for supplying rural communities with water for domestic purposes. Protecting these water sources from contamination is an natural way of ensuring the continuity of this supply.

Suitability

This technology is suitable in locations where springs occur and no unresolved pollution problems prevail. They may be managed as point sources for communities or distributed to individual households by connection to a distribution system.

Environmental Benefits

No environmental impacts have been reported.

Advantages

The advantages of this technology are several-fold: groundwater is a relatively safe water source for use without treatment, springs are the most inexpensive source of groundwater, and spring protection structures can be constructed using local skills and materials. Further, this technology incurs few or no operating costs, and requires very little maintenance, if the water is obtained at its source.

Disadvantages

Service level is dependent on groundwater yields, which seldom can be improved (unlike in conventional systems). Further, there is difficulty in ensuring the hygiene of the springs, especially during the rainy season when it is not always possible to protect the spring from surface water intrusion. The location of springs is not always near the point of consumption and, in many cases, access is difficult. Springs may also run dry during times of drought.

Cultural Acceptability

Spring water is associated with witchcraft amongst some East African communities. It is also the belief in some communities that women who have given birth to twins and/or whose husbands have died must not use springs before certain cleansing rituals are performed for fear that their “unclean” condition would cause the springs to dry up.

In Southern Africa, communities often associate the placement of cement on springs with the spring drying. Such communities would be reluctant to install concrete catchments around their springs.

Further Development of the Technology

The technology does not require any further technical development, but it may be necessary to carry out social research on the cultural beliefs of communities to determine their basis and the effect this has on spring protection.

Information Sources

Contacts

Ministry of Land Reclamation Regional and Water Development, Post Office Box 30521, Nairobi, Kenya, tel (254 2) 716103.

Blair Research Laboratory, Post Office Box CY 573, Causeway, Harare, Zimbabwe, Tel. 792747

Bibliography

SKAT 1987. Manual for Spring Catchments.

Kenya-Finland Western Water Supply Programme 1990. Water Supply Development Plan 1990 -2005. Ministry of Land Reclamation Regional and Water Development, Nairobi.

WHO (World Health Organization) 1992. Fact Sheets on Environmental Sanitation for Cholera, WHO Publication No. WHO/CWS/92.17, Geneva.

2.1.2 Rock and roof catchments

Technical Description

Rock catchments are simple systems for the collection of rainwater. Siting of these structures should take into account ease of access of the users and the geological structure of the site. The best sites are found on the lower reaches of bare rock inselbergs, where runoff losses to the soil, vegetation and structures is minimised. Storage may be provided in dams or open tanks.

Roof catchments are suitable for individual household use, and use in schools and other institutions where sufficient impermeable roof cover exists. To collect rainwater from roof catchments, gutters and ground storage tanks are required (Figure 28). “First flush” water from each shower should be prevented from entering the storage facility to reduce the degree of pollution of the stored water by dust, leaves and bird droppings washed from the rooftop into the reservoir. Underground tanks may also be used (Figures 29 and 30).


Figure 28. Lateral view of a rainwater catchment system.

When calculating the size of the storage for rock or roof catchments, the demand for water, and the length of the dry periods, must be considered. The required catchment area also depends on the amount and variability of rainfall. In most cases, however, the available area is often the limiting factor due to local conditions.


Figure 29. Rock catchment with underground storage tank.

Extent of Use

This technology is extensively used in arid and semi-arid areas of Africa, such as Mauritania, Benin, Burkina Faso, Uganda and Kenya.

Operation and Maintenance

Limited regular maintenance of gutters, and removal of leaves and other debris from the catchment surface, is required. Cleaning of the tanks is necessary before and after the first rains. All of these activities can be handled by the community. Water is drawn by bucket or taps fitted to the storage tank.

Level of Involvement

This technology is installed and operated primarily by local communities, sometimes using hired labour. Technical advice from government, NGOs, or private sector agencies may be required. Once the technical training of locals has been completed, the roof catchment system installation and management can be left in the hands of the householders.

Costs

In 1994, a typical roof catchment system in Benin, constructed of ferrocement, cost $346/7 m3 storage, $496/12 m3 storage, or $800/24 m3 storage. In Burkina Faso, Uganda and Kenya, costs ranged from $852/20 m3 storage, constructed of ferrocement, to $1016/30 m3 storage constructed of masonry.

Effectiveness of the Technology

Rain water catchment systems have been successfully utilized by people all over the world for many centuries. Presently, rain water is collected from many types of surfaces to provide water for domestic, livestock, agricultural and fish-farming use. Rain water is also used as a

The effectiveness of rain water collection systems depends on the type of roofing material used. For example, thatched grass gives lower yields than corrugated iron sheets.

Environmental Benefits

No environmental benefits have been reported.

Suitability

This technology has good potential in areas of rugged and steep terrain. It is more feasible in high rainfall areas, because rain can fill the storage reservoirs more frequently. On the other hand, it is quite suitable for arid and semi-arid areas where rain water is the most accessible water source. It also has good potential for community management.

Advantages

The advantages of using this technology are that water is provided at the point of consumption, and there is good potential for community-based management of the collection systems (with low operating and maintenance costs). Relatively good quality water can be obtained using this technology.


Figure 30. Artificial roof catchment with ground water storage tank.

Disadvantages

Disadvantages of this technology include difficulties in controlling the water quality, an high per capita cost of development, and a lack of reliability as a source of water. It cannot serve large users, although, it is usually adequate to provide a low level of service, suitable for family use.

Cultural Acceptability

No negative cultural factors have been observed.

Further Development of the Technology

There is very little that needs to be done to further develop this technology.

Information Sources

Contacts

Ministry of Land Reclamation Regional and Water Development, Post Office Box 30521, Nairobi, Kenya.

CREPA, Ouagadougou BP. 7112, Ouagadougou, Burkina Faso, tel 310359, fax: 310361.

The Institute of Agricultural Engineering, Post Office Box BW330, Borrowdale, Harare, Zimbabwe.

AGRITEX, Post Office Box CY 639, Causeway, Harare, Zimbabwe.

Ministry of Agriculture, Private Bag 003, Gaborone, Botswana.

Ministry of Agriculture, Post Office Box 92, Maseru 100, Lesotho.

Coordenacao Geral dos Projectos Integrados, Prorural, Ruo da Resistencia 1746, Maputo Mozambique.

Direction de l'hydrologie et d'hydraulique. Programme d'Hydraulique Pastorale, Mauritane, Tel. 251611, Fax 251602.

Bibliography

Hissen-Petersen, E. and M. Lie 1992. Harvesting Rain Water in Semi-arid Africa, Nairobi.

Kenya-Finland Western Water Supply Programmes 1990. Water Supply Development Plan 1990-2005. Ministry of Land Reclamation Regional and Water Development, Nairobi.

Direction de l'hydrologie et d'hydraulique 1978. Programme d'Hydraulique Pastorale: survie du betail en Mauritane, 356 p.

2.1.3 Fog harvesting

Technical Description

Fog droplets are much smaller than both raindrops and drizzle drops, with diameters varying from 1 to 40 microns, and fall at velocities ranging from less than 1 cm/s to about 5 cm/s. These low velocities result in fog droplets being influenced even by light winds that can cause the droplets to travel almost horizontally. An appropriate fog droplets-collector, therefore, is a vertical or near vertical surface. Such surfaces can be constructed as vertical mesh panels on which fog droplets are intercepted and condensed.

Extent of Use

Fog harvesting is a rarely used technique in Africa. In Namibia, for example, the technology is still in the experimental stage. However, the actual application of this technology on a limited basis did begin in late 1995, as a project of the Ministry of Agriculture, Water and Rural Development.

Operation and Maintenance

Operational requirements include the measurement of the volume collected and the recording of meteorological data, either manually or by automatic weather station, since changes in weather conditions may change the operational design of the harvesters. Problems encountered include dust, rodents, game, and irregular fog formation. However, virtually all of the input materials to construct, operate and maintain the system are available locally.

Costs

The input costs are not yet known. However, an automatic weather station costs about $50 000 to purchase and install.

Effectiveness of the Technology

A surface area of about 50 m2 can harvest a significant amount of fog and convert it into water. However, experimental data from the system in Namibia are still forthcoming.

Suitability

Fog harvesting is suitable in regions which have hills or mountains close to potential users, on a coastline with a cold current offshore. The quantity of derived water is a function of the scale of the project and the fog available. In Namibia, the resulting water is slightly salty as a result of the inclusion of some marine aerosols, and contains some dust.

Environmental Benefits

No direct environmental benefits have been reported or are foreseen.

Advantages

No extensive, permanent structures are necessary to implement this technology, and the derived water is normally potable. The technology can easily cater to the water needs of coastal, or desert, settlements or camps currently relying on a saline water source or some other expensive option such as tanker delivery. The water is available within the demand area and therefore requires little, if any, pumping. The water source is also sustainable over many years. Clouds normally bring a large amount of water and extend over a wide front. Therefore, the amount of water collected can be varied by varying the number of collectors installed. The collectors are simple and require no energy other than the wind.

Disadvantages

Deforestation can lead to reduced fog water inputs. Further, it may result in dust and other pollutants entering the harvested water.

Information Sources

Contacts

P. Heyns, Department of Water Affairs, Ministry of Agriculture, Water and Rural Development, Private Bag 13193, Windhoek, Namibia, Tel. 061-263141, Fax 061-263222.

D. Lucks, Department of Water Affairs, Ministry of Agriculture, Water and Rural Development, Private Bag 13193, Windhoek, Namibia.

Bibliography

Heyns, P. 1995. Desalination Development in Namibia, New World Water.

Schemenauer, R.S. and P. Cereced 1994. Fog Collection's Role in Water Planning for Developing Countries. Natural Resources Forum, 18 (2): 91-100.

2.1.4 Groundwater abstraction in urban residential areas

Technical Description

This is the abstraction of groundwater through boreholes, by private householders or water supply agencies.

Extent of Use

The technique is extensively used in a number of countries in Africa. In rural areas, it may be the only reliable source of water supply. In urban centres, it augments conventional municipal supplies.

Operation and Maintenance

The operation and maintenance requirements for groundwater abstraction systems usually relate to type of pumping system used. For poorly constructed boreholes, collapse may be experienced.

Level of Involvement

Both household and water supply agencies make use of this technology.

Costs

Borehole drilling and components costs have been estimated to be about $3000 for a typical installation. Energy costs depend on source of energy used, usually the cost of electricity.

Effectiveness of the Technology

Household use of groundwater reduces demand for treated urban water. It is also efficient for industrial use since each industry can treat the water to meet its own requirements.

Suitability

This technology is suitable in all areas with groundwater reserves, in particular, during droughts.

Environmental Benefits

There could be environmental damage from over pumping as the water table recedes. In years of water shortage, this over-pumping may negatively affect the groundwater discharge into rivers, lakes and reservoirs.

Advantages

The advantages of this technology include its site-specificity; no significant delivery (reticulation) systems are necessary. The technology may be used where urban services are poor or unreliable.

Disadvantages

Over pumping may lead to ground subsidence. Subsidence is of great concern in crowded urban areas. Further, groundwater is susceptible to contamination from wastes.

Cultural Acceptability

Generally, there are no cultural problems with the use of groundwater supplies.

Further Development of the Technology

Techniques for the rapid assessment of safe yield to avoid over pumping are required.

Information Sources

Simpson, G.C. 1990. Research into Groundwater Abstraction in Residential Areas. Vol 1. Water Research Commission Report No. 211/1/90, Division of Building Technology, CSIR, Pretoria.

2.1.5 Groundwater abstraction using handpump-equipped wells

Technical Description

Handpumps tap groundwater from shallow or medium depth aquifers and from deep aquifers if the at rest water level is high enough. Handpumps are water conveyance systems used to bring groundwater to the surface. There are a number of such pumps in operation in Africa and numerous textbooks provide specific descriptions of these devices (Figure 31).

Figure 31. Some commonly used handpumps.


Model “B” bushpump


Volantia pump


Afridev pump

In normal circumstances, handpumps are installed in wide diameter wells, which can be constructed by hand to depths of up to about 15 m, or drilled by rigs to much greater depths. The type of well most widely used is the hand-dug well, which is one of the cheapest means for providing a small supply of water in rural areas. A depth of about 10 to 20 m is usually considered the limit of practical manual sinking. The diameter of the well should not be less than 1.2 m, allowing two persons to work together in the well. A lining, that serves several purposes, should be used as the well is sunk. The lining is a protection during construction against caving and collapse, and retains the well wall after completion. There are many materials suitable for linings; e.g., masonry, brickwork, and plain or reinforced concrete. On the bottom of the well, it is usual to place a filter of graded layers of gravel to prevent the ground material from being drawn upwards into the well with the water. At the surface, the lining of the well should be raised at least 0.6 m above ground level and provided with a protection platform to channel drainage away form the well,

Small diameter wells may also be constructed by means of an auger. The auger, which is usually about 100 mm across, may be rotated by hand. Mechanised augers, or power augers, are also available. Once the water-bearing layer has been penetrated, the necessary length of piping, tipped with a screened wellpoint, or strainer, is lowered into the hole; a pump attached to its upper end, and the well “cleared” by pumping.

Tube wells consist of a perforated or screened pipe which is jetted or driven into the groundwater-bearing aquifer. Tube wells can yield large quantities of water, but the depth to which they can be driven is limited and the ground formation must be appropriate for their use. Their most common application is in the extraction of groundwater from water-bearing sands, especially those forming the beds of ephemeral streams. Tube wells can also be installed in perennial rivers, making use of the natural filtering properties of sandy beds of the rivers by drawing water through the river beds instead of from the rivers themselves. The pipes are usually 25 to 100 mm in diameter. The wells constitute a good means of obtaining water from areas with relatively coarse sand.

Extent of Use

Wells using handpumps are extensively used throughout Africa.

Operation and Maintenance

The operation and maintenance of handpumps varies depending on the type and complexity of the pump. Attempts at designing a reliable pump which can be maintained at the village level continue. Experimentation with these village level operation and maintenance (VLOM) schemes are shifting gradually to focus on institutional-level operation and maintenance. Preventative maintenance operations carried out by villages and institutions include greasing moving parts (taking care not to contaminate the water supply with oils and greases), tightening bolts, replacing seals (for some pumps), and cleaning the surroundings.

Level of Involvement

Local inputs to implementation of this technology are generally in terms of skilled labour and materials. Technical advice may be necessary in the conduct of hydrogeological investigations and well drilling.

Costs

While hand dug wells are quite inexpensive, boreholes drilled by rigs are fairly expensive in terms of initial capital costs. Dug shallow wells and augured tube wells have a per capita construction cost of $6 to $20, with an operation and maintenance cost of $0.02 to $0.14 per capita per year. Machine-drilled boreholes, equipped with a hand pump and serving a population of about 200 to 300 people, will have an estimated per capita construction cost of $19 to $23, and an operation and maintenance cost of $0.26 to $0.52 per capita per year.

Effectiveness of the Technology

The delivery rate of most handpumps is around 20 l/min, and their ease of operation makes them ideal for rural operations.

Suitability

Dug wells are an appropriate option in areas where groundwater is less than 20 in below ground level. Augured tube wells, dug using motorised and/or manual rigs and augers of limited penetration, are appropriate in areas in which groundwater occurs at depths between 20 and 35 in. Motorised, conventional drilling rigs are an ideal means of developing water supply sources in areas where groundwater occurs at depths greater than 35 m below ground level, or in hard rock between 20 and 25 m depth, where the weathered material is thin.

Environmental Benefits

The existence of a well may lead to increased erosion in its immediate vicinity. However, wells are focal points for other development such as the planting etc.

Advantages

Well water is relatively safe without treatment. Hand dug wells are inexpensive and can be constructed using local skills and materials; community participation is easy to organize. Further, the operation of handpumps requires no external power and few skills, and the pumps may be maintained by local technicians. The use of spare parts is small.

Disadvantages

The capacity of a well is limited, and service supply levels are lower than in piped schemes supplied from conventional sources. Hand dug wells are reliable only in areas where good quality groundwater is available at shallow depth. The hygienic quality of the wells, especially shallow wells, is not always satisfactory as a result of surface water intrusions leaking through the slab and superstructure, and around the pump casing.

Cultural Acceptability

There are no cultural problems in utilizing groundwater for domestic purposes. However, communities do not like wells to be developed too close to sacred places such as shrines.

Further Development of the Technology

There is need to improve on the methods of digging the shallow wells. Also, the handpump needs further developmental work to make it more suitable for village level operation and maintenance. Maintenance systems require further development to ensure sustainability.

Information Sources

Further information can readily be obtained from the Departments of Water in the various countries, and also from organisations such as UNICEF, World Vision, CARE, and Save the Children, among others.

2.1.6 Rope-washer pump

Technical Description

The rope-washer pump consists of a rope with knots or rubber washers, whose diameters are slightly less than the diameter of the pipe, placed at intervals along it (Figure 32). This assembly is drawn up inside a rising pipe, and is capable of drawing relatively large volumes of water to the height of the pump. During operation, the pipe is inserted into water and the rope drawn upwards through the pipe by means of a winding drum with a crank. Water is also drawn up and discharged at the top. The rope and washers pass round the winding wheel and return to the bottom of the pipe thus completing the circuit. This design can be modified to avoid slippage of the rope on the pulley by using old tyre casings to make the pulley wheel. To prevent the washers getting caught, and to support the bottom of the pipe above the bottom of the well or river bed, a suitable pipe stand and rope guide is necessary. Friction should be kept low by allowing leakage between the washers and the pipe stem.


Figure 32. The rope and washer pump (Lambert, 1990).

Extent of Use

The rope-washer pump is receiving moderate use in Kenya, Zimbabwe and Burkina Faso.

Operation and Maintenance

Rope-washer pumps rely are manufactured locally, and, therefore, are amenable to local repair and maintenance using simple, locally-available materials.

Level of Involvement

The components of this technology are community-manufactured and operated. Government and NGOs are often involved in the promotion of this technology and development of refinements.

Costs

Rope-washer pumps cost between $30 to $50 to construct. The construction cost increases in proportion with the lift required.

Effectiveness of the Technology

This technology is appropriate for all domestic uses and micro-irrigation or garden irrigation uses. This pump can pump high volumes with a low lift.

Suitability

The technology is suitable for abstraction from shallow wells of up to 10 m depth or from rivers and streams. It is easily adaptable to changing volumes by adapting the diameter of the pipe and washers.

Environmental Benefits

The introduction of a simple device such as the rope washer pump, lends itself to micro-scale gardening and the accompanying positive environmental management practices.

Advantages

The pump has no valves and does not require complicated bearings. It is easy to manufacture, with local resources, and is ideal for flood irrigation of small gardens.

Disadvantages

The pump has limited lift and poor pumping efficiency, as water is allowed to leak through the valves.

Cultural Acceptability

There are no known cultural inhibitions.

Further Development of the Technology

The rope-washer pump technology needs to be further disseminated to gain additional field experience of its operation. The efficiency of the pump needs to be improved.

Information Sources

Chleq, J.L. and H. Dupriez 1988. Vanishing Land and Water. Soil and Water Conservation in Drylands. Macmillan, 117 p.

Lambert, R.A. 1990. How to Make a Rope Washer Pump. Intermediate Technology Publications, London.

2.1.7 Artificial groundwater recharge

Technical Description

Artificial recharge is the use of infiltration basins (Figure 33) or injection wells (Figure 34) to recharge groundwater resources. Infiltration basins can take many forms. For example, a storage dam can function as an infiltration basin under certain conditions. With infiltration basins, it is essential to construct the pond on an infiltration zone lying above an impermeable layer.


Figure 33. Recharge by infiltration basin.


Figure 34. Recharge by injection well.

Extent of Use

Infiltration basins and injection wells have been implemented in Botswana, Egypt, Tunisia, and Algeria. In Zimbabwe, small infiltration dams are being developed.

Operation and Maintenance

There is need for a source of the water to be recharged. Groundwater recharge using infiltration basins in areas with high evaporation rates is not likely to be effective. Likewise, the presence of clay lenses covering parts of an aquifer can be a problem as they can prevent the infiltrated water from reaching the aquifer. Both problems can be overcome through the use of injection wells, which allow the recharge water to be inserted into an aquifer under pressure.

Level of Involvement

Construction of recharge basins can be undertaken by local personnel with experience in well digging. Government assistance may be required to identify appropriate recharge sites.

Costs

The costs are moderate, depending on the scale of operations.

Effectiveness of the Technology

Recharged water may take on the qualities of normal groundwater, as impurities are removed within the soil profile. However, there is also the possibility of introducing contaminants into the groundwater system through the use of this technology, depending on the source of the recharged water. Groundwater recharge as a stormwater management technology creates the least cause for concern, and ensures the reliability of water supplied from nearby wells.

Suitability

This technology is appropriate for arid regions lacking alternative water sources. Water reclaimed in this fashion may be used as an alternate source of drinking water. Recharge may be appropriate in areas where behaviour of naturally-occurring groundwater is uncertain.

Environmental Benefits

The construction of infiltration basins may help to control soil erosion. The basins are usually appropriate habitat for a number of birds and wild animals.

Advantages

Groundwater recharge, especially using injection wells, conserves water through reduced evaporation. Clean drinking water may be recovered from wells in the vicinity of the recharge field without using complicated treatment systems.

Disadvantages

The water from a recharged aquifer cannot be used without a system of abstraction. There is also a possibility of polluting the aquifer with the recharged water.

Cultural Acceptability

The technique is culturally acceptable.

Further Development of the Technology

There is limited scope for further development of technology, especially in terms of ensuring the quality of the recharged water and the prevention of groundwater contamination.

Information Sources

Gustafsson, P. and J. Johansson s.d. A Study of Water Resources in Botswana. Department of Geology, Chalmers University of Technology and University of Goteborg, Goteborg, Sweden.

2.1.8 Well-tank borehole well

Technical Description

This is a type of borehole in combination with a well. The latter serves as storage. This technology is used in cases where hydrogeological conditions are such that neither structure alone can meet the operational needs of the beneficiaries.

The borehole is drilled to groundwater level, and the well-tank, which is 0.5 m to 1 m away from the borehole, is drilled to a depth such that the static level of the borehole is at least 6 m higher. This difference in elevation provides a sufficient water level in the well to permit easy abstraction of the stored water. This water depth in the well-tank is maintained by the construction of a junction between the well-tank and the borehole at the bottom of the well-tank at the static water level (Figure 35).


Figure 35. Well tank - borehole well.

Extent of Use

This technology has been used in projects in Mauritania. Similar systems, with slightly different arrangements of the components, exist in Egypt, Libya and Sudan.

Operation and Maintenance

Since the well-tank is below the static water level in the borehole, water enters the well-tank by gravity through the perforated junction between the well and the borehole. The depth of water in the well-tank becomes that of the borehole. Abstracting of water is carried out in the traditional way from the well-tank. Maintenance is carried out periodically by cleaning the well-tank as and when necessary. The well-tank should be protected against contamination as described elsewhere in this volume.

Level of Involvement

The capital investment in the borehole may be prohibitive for individuals, but the technique can be established jointly by individuals within communities. The technology can be implemented with limited technical support from extension agencies.

Costs

The costs include the drilling costs of the borehole and well-tank, on the one hand, and the cost of providing the superstructure of the well, on the other. The cost per linear metre of establishing the borehole, which can be up to between 100 m and 400 m deep, is over $300.

The cost of establishing and protecting the well is between $260 and $408/linear metre.

Effectiveness of the Technology

The borehole well is as efficient as the simple well, and, generally, is more reliable. The well-tank system experiences fewer seasonal fluctuations in water level compared to other wells in the regions in which the technology has been applied, and, as a result, rarely dries up.

Suitability

Well-tanks are adaptable for use in all terrains. However, in areas with discontinuous aquifers, where groundwater is captured in very hard, fractured geologic structures, and/or where wells cannot readily penetrate the substrate, storage can be provided by surface cisterns. Similarly, in sedimentary basins, shallow wells may be more appropriate storage structures.

Environmental Benefits

Use of this technology makes groundwater readily available at the surface. If used within conservation areas, this technology can provide water for environmental rehabilitation programmes, especially in areas where this would otherwise be impossible. However, care should be taken to avoid over-abstraction of groundwater, and prevent contamination of groundwater from surface sources.

Advantages

Use of this technology allows the use of simple abstraction methods, and can provide a reliable source of water.

Disadvantages

The technology has an high capital investment cost, and is dependent upon a reliable groundwater source.

Cultural Acceptability

There are no known cultural inhibitions relating to the use of this technology.

Information Sources

CIEH, 01 BP 369 Ouagadagou 01, Burkina Faso, Tel. 307112, Fax: 362446.

2.1.9 Cisterns

Technical Description

Cisterns are an ancient method of water harvesting, dating back to the early Roman empire. There are artificial reservoirs constructed by excavating bedrock, such as limestone, to depths of between 3 and 7 metres to provide water storage throughout the Roman world. While serving a similar purpose, modern cisterns are usually built with cement blocks or fired bricks.

Cisterns collect water in the form of runoff from a rock-lined catchment or other suitable, nonporous surface. There is commonly a settling basin at the cistern entrance which serves to settle sediments borne by the runoff. A screen is also provided to remove larger particulates.

Extent of Use

This technology is used in a number of north African countries, where it is known by a variety of different names. These names are indicated in brackets. The technology is used in Libya (where it is known as Fusqia or Majen), Algeria (Sahrij), Egypt (Roman reservoir), Tunisia (Fuskia pool), Morocco (Al Majel), and Sudan (ground reservoir).

Operations and Maintenance

Routine maintenance is necessary to reduce losses to leakage by repairing cracked walls. There is also a need for the periodic removal of sediments which might choke the entrance.

Level of Involvement

This technology can be constructed, operated and maintained by villagers.

Costs

The cost of implementing this technology is reasonably low, as most of the construction of the cisterns can be done by communities. However, mechanization is increasingly used for the digging of the cistern, which increases the cost.

Effectiveness of the Technology

The volume of water harvested depends on the amount of rainfall and the size of cistern. Major losses of water generally occur in the catchment area, through infiltration and evaporation, rather than from the cistern itself, provided the cistern is maintained.

Suitability

The technology is suitable for use in all regions of Africa and is similar to rock catchment systems. In areas of high evaporation, the cistern should be covered to minimize evaporative losses.

Environmental Benefits

The use of cisterns to capture runoff has no known negative environmental effects, and can provide water for a variety of environmental purposes in dry areas.

Advantages

This technology has the advantage of being a simple, low cost technology which can increase the yield of water from rock catchment systems.

Disadvantages

Use of this technology may require provision of an abstraction system to draw the water from the cistern. Because of the likelihood of contamination from surface sources, this technology is not ideal for use as a potable water source.

Cultural Acceptability

This technology is culturally acceptable by the communities in which it has been used.

Information Sources

UNESCO Regional Office for Science and Technology for the Arab States, Arab Centre for Studies of Arid Zones and Dry Lands (ACSAD) 1986. Regional Project on Rational Utilization and Conservation of Water Resources in the Rural Areas of the Arab States with Emphasis on the Traditional Water Systems, UNESCO Project ROSTAS/HYD/1/86.

2.1.10 Palm petioles

A suitable tree is planted in the homestead grounds. Suitable trees usually have broad leaves which collect rainwater which is channelled to a collecting pot (Figure 36).

Figure 36. Various methods of collecting rainwater using:


trees

leaves

plant materials.

Extent of Use

This technology is used in Nigeria.

Operation and Maintenance

The technology has very limited maintenance requirements.

Level of Involvement

The technology is usually used by individual households.

Costs

Costs are negligible, and, depending on the type of tree used, may result in a net profit to the householder.

Effectiveness of the Technology

The effectiveness of this technology depends on the effectiveness of the collecting channel. There are often significant losses resulting from spillage and other leaks within the system.

Suitability

The technology is suitable for collecting small volumes of water at the household level.

Environmental Benefits

Use of this technology promotes the growing and maintenance of trees. It may encourage the propagation of indigenous vegetation.

Advantages

It is a low cost technology that does not require extensive knowledge to construct or complex equipment to operate.

Disadvantages

Large volumes of water cannot be collected using this technology. Also, the water may be contaminated with dust, insects and bird droppings as well as plant material.

Cultural Acceptability

The technology is culturally accepted in those areas where it is practised.

Information Sources

United Nations University, Institute for Natural Resources in Africa, ISSER Building Complex, Nasia Road, University of Ghana, Accra, Ghana.

2.2.1 Denitrification of groundwater

Technical Description

Denitrification is the process whereby nitrogen is removed from water. When employed in water quality improvement technologies, denitrification treats water to reduce its nitrate-nitrogen content to potable levels. There are three principal approaches to nitrate removal: ion exchange, chemical reduction and biological denitrification. The first two are well-documented in various publications (Gauntlett, 1975; Metcalf, 1975) and are not, therefore, further described here.

With biological denitrification, aerobic heterotrophic bacteria, under anaerobic conditions, utilise the oxygen molecules that, together with nitrogen, form nitrate. This oxygen is used in place of dissolved elemental oxygen. Removal of the oxygen molecules converts nitrate to nitrite, ammonia or nitrogen gas. This process is common in water-logged soil and other aquatic environments. Within the organisms, the nitrate-derived oxygen acts in the same manner as elemental oxygen, as an acceptor for electrons and hydrogen. Chemical energy to drive the process is added in the form of organic carbon, methyl alcohol, ethanol and acetic acid.

When this process is used to treat water, there is need to create an environment for the bacteria that mimics the soil conditions in which this process occurs naturally. This environment is generally created in biological reactors, like attached growth reactors (packed columns, rotating disc units and fluidized bed columns), suspended growth reactors and underground reactors for the treatment of nitrates, in order to bring the denitrifying bacteria into contact with the water to be treated (Figure 37). Generally, also, the chemical energy needs to be added artificially to the system to stimulate the denitrification process. Thus, a denitrification plant, in its most basic form, comprises an injection well for adding nutrients, a biological reactor, and a pumping well for the abstraction of treated water.

Extent of Use

This technology has been used in projects in South Africa.

Operations and Maintenance

Denitrification technologies have high energy requirements associated with the suspended growth reactors. Electrical energy is required in order to keep the bacterial floe in suspension by stirring. Chemical energy sources are also required in many systems. The use of methyl alcohol as a carbon source has economic and operational advantages because of the resulting low solids production (Dahab, 1988).

With underground biological denitrification, problems may arise as aquifer pore spaces clog with biological matter. In such cases, the recommended approach is to undertake denitrification in an above-ground biological reactor with underground recirculation of the treated water as a secondary treatment.

Figure 37. Groundwater denitrification unit (Latimela, 1993).


(a) Sectional view of underground denitrification.


(b) Sectional view of aboveground denitrification with groundwater recharge.


(c) Plan view of sections.

Level of Involvement

This technology requires specialised skills and knowledge to operate effectively. Thus, while communities can participate by funding the units and their installation costs, government participation is required to design, install, operate and maintain the systems.

Costs

Biological denitrification has been found to be cheaper than ion exchange (Latimela, 1993). The treatment costs for a design capacity of 20 m3/day were found to be $0.26 /m3. The capital and operating costs for biological denitrification for a 10 m3/day capacity were found to be:

capital cost/m3

$0.33

running cost/m3

$0.07

treatment cost/m3

$0.40

Suitability

This technology is suitable for the reclamation of nitrate-contaminated groundwater.

Advantages

Denitrification technologies remove nitrate from the waters to reduce the risk of methaemoglobinaemia in infants and others. Use of biological treatment methods do not require regeneration of media and, hence, there is no problem of brine disposal. With underground denitrification, both denitrification and secondary treatment are performed in situ, reducing the need for infrastructure.

Disadvantages

Because this is a biological system, there will be fluctuations in quality. In some cases, there may be a sensitivity within the service population to bacterial toxins.

A large bacterial population, free of pathogens, has to be developed. If the system breaks down, this bacterial mass may be lost. Should this happen, no further treatment of water is possible until the bacterial population is reestablished.

Further Development of the Technology

Further studies are essential to determine the potential of aquifer pore spaces to clog with biological matter under operational conditions, and to identify suitable remedial measures to overcome this problem short of reconstructing the system as an above-ground reactor. Development is also needed to ensure a more constant output water quality from these systems.

Information Sources

Dahab, F. and Y.W. Lee 1988. Nitrate Removal from Water Supplies Using Biological Denitrification. Journal of the Water Pollution Control Federation, 60 (9): 1670-1675.

Latimela, O.N. 1993. Denitrification of Ground Water for Potable Purposes. Water Research Commission Report No. WRC 403/1/93, Pretoria, South Africa.

Pelczar, M.J., E.C.S. Chan and N.R. Krieg 1986. Microbiology, 5th Edition. McGraw-Hill Book Company, Boston.

Gauntlett, R.B. 1975. Nitrate Removal from Water by Ion Exchange. Water Treatment Examination, 24 (3), 172-193.

Metcalf and Eddy, 1979. Wastewater Engineering: Treatment, Disposal and Reuse, 2nd edition. McGraw-Hill Book Company, Boston.

2.2.2 Iron removal

Technical Description

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.


Figure 38. Schematic of a typical iron removal unit - coupe AA


Figure 38. Schematic of a typical iron removal unit - coupe BB

Costs

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%.

Suitability

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.

Advantages

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.

Disadvantages

If not cleaned periodically, the system may become blocked with the iron floe.

Cultural Acceptability

This technology is culturally acceptable in areas where it is used.

Information Sources

Contacts

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.

Bibliography

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.

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.

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 51 of water that is not turbid; two seeds will purify between 2.51 and 51 of water that is slightly to moderately turbid; and three seeds will purify 2.51 of very turbid 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.

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.

2.2.4 In-stream water quality upgrading

Technical Description

A typical water quality enhancement unit consists of a low diversion dam, infiltration gallery and clear water reservoir. A low diversion dam is constructed using a pile of rocks bound together with cement or mortar. The filter box is constructed of concrete according to designed specifications. There could be one or two filter boxes depending on the quality of the stream water. The filter box is then filled with a filter media which is comprised of 20 cm of gravel and 1.2 m of sand packed on top of the gravel. The inlet end of the intake pipe is covered with nylon mesh to prevent large suspended particulate matter from entering the intake pipe. The portions of the pipe within the filter boxes are perforated. Using such an arrangement, water could flow from a raw water source onto a filtration medium through which it is filtered and advanced to the collection well, all under gravity. The clear well reservoir, in which the filtered water is collected, is constructed of concrete. The size of the reservoir depends on the size of the population.

Having been provided with a design, the construction of this system can be accomplished by a community with the help of local artisans living in the community. A typical unit, constructed on the Nima Creek in Accra, Ghana, was designed to deliver a minimum of 30 litres/person/day into the filtered water well (Figure 40). This well was 5 m deep and 2 m wide, extending 2 m below the water table in depth. The filtered water in this system was accessed by using a handpump fitted onto the collection reservoir. However, for small communities with populations of 1 000 or less, outlet pipes with valves fitted to the clear water well are cheaper alternatives.

Extent of Use

This technology has been used widely in some rural communities in Ghana. In the last twenty years, however, the technology has not been actively used, having been replaced by other technologies for rural water supply, augmented by the electrification scheme started by the government. Nevertheless, the technology has recently been revisited and improved for application in rural water supply.

Operation and Maintenance

The local residents operate and maintain the system using simple tools. Preventive maintenance involves cleaning the nylon mesh cover of the intake pipe two to three times per week.

Level of Involvement

This technology was adopted as a community built and managed system. The planning and design of the system are the only aspects of the project which require the involvement of expert personnel.


Figure 40. Infiltration gallery on the Nima Creek, Accra, Ghana.

Costs

A community can develop this technology with very little guidance. The approximate costs of construction are as follows:

Intake civil works

$15/m

Filtration gallery and clear water well civil works

$600.

Suitability

This technology is suitable for low income, rural communities that cannot finance and sustain conventional water supply systems. It is also suitable for refugee camps where electric power supplies are not available, or in other areas where chemicals and equipment for water purification are difficult to obtain.

Advantages

The technology is low cost and needs no power supply, no chemicals, and few spare parts to function. It can be constructed, operated and maintained by semi-skilled people in local communities.

Disadvantages

It is difficult to backwash the filter without a power source; thus, the quality of the filtered product water and a satisfactory filtration rate may not be sustained. In such situations, the filtration media may have to be replaced on a frequent basis for best efficiency and quality of product water.

Further Development of the Technology

Development of methods for backwashing the filter material is necessary to maintain the sustainability of the system.

Information Sources

S. Mintah-Boateng Asare, Construction and Operation of Infiltration Galley System, Water Resources Research Institute (CSIR), Post Office Box M, Accra, Ghana.

(introduction...)

Waste Stabilization Ponds

Technical Description

Waste stabilization ponds consist of:

(i) preliminary treatment stages which include a screening chamber for the removal of large solids, a grit chamber for the removal of grit and other inert materials, and a flow recording system;

(ii) facultative ponds, which are responsible for the removal of BOD5 largely through sedimentation and biological degradation; and,

(iii) maturation ponds, which are responsible for the removal of pathogens through exposure of the pathogens to conditions inhospitable to the microorganisms.

Where the ponds are expected to treat “strong” wastes, anaerobic pretreatment ponds may be installed upstream of the facultative ponds.

Extent of Use

Ponds are extensively used in Africa for the treatment of urban waste.

Operation and Maintenance

At the pond edge, maintenance involves the removal of grasses to limit mosquito breeding habitat, plugging holes caused by birds and rodents, and maintaining pumps were necessary.

Level of Involvement

Municipal artisans or technicians of similar qualification and/or experience are required to operate and manage these facilities.

Costs

This technology is low in cost in comparison with other treatment systems.

Suitability

Ponds are suitable in most countries of Africa.

Effectiveness of the Technology

Ponds are effective in removing BOD and suspended solids.

Environmental Benefits

This technology is not capable of removing nutrients, which may lead to the enrichment of the receiving waters (eutrophication).

Advantages

The technology is effective in removing BOD at low cost

Disadvantage

Ponds demand a large land area and cannot remove nutrients.

Cultural Acceptability

Residents complain of smell if homes are built too close to a poorly operated and maintained plant.

Further Development of the Technology

Ponds work well but need more research to improve design efficiency and enhance nutrient removal capabilities.

Information Sources

Standard textbooks and more specifically work by Marais (South Africa) and Mara (Zambia).

Wastewater recycling and reuse technologies fall into three major classes:

• Direct reuse
• Indirect reuse
• Internal reuse (described under “Mining and Industry”, below)

These three classes have different technical descriptions, extents of use, and operation and maintenance requirements, but are otherwise similar. The technical descriptions for the different wastewater treatment systems are given in the text boxes below. Because these are well-known technologies, numerous engineering texts exist which detail aspects of their design, construction and operation. Standard text books should be referenced for such detailed descriptions.

2.3.1 Direct reuse of treated municipal wastewater

Technical Description

Direct reuse involves the abstraction of effluent from sewage treatment works and, after further treatment (e.g., tertiary treatment or retention in maturation ponds), mixing it with raw water at the inlet of a water treatment works.

Extent of Use

This technology is extensively utilized in Southern Africa, especially in South Africa, Namibia, Zambia and Zimbabwe, as well as in Mauritania and Burkina Faso in West Africa.

Operation and Maintenance

Catchment quality control is essential. This involves the segregation of industrial effluents from the catchment of the reclamation plant to avoid contamination with persistent organic contaminants, heavy metals, and other substances deleterious to human health. The wastewater should undergo the both biological and physico-chemical treatments: chemical coagulation and flocculation; solids separation; disinfection; activated carbon filtration; reverse osmosis filtration; and stabilisation. These steps may be considered to be routine water reclamation stages. Further, because of the flocculation and solids separation stages, sludge management practices are required when using this technology. There is a need for a steady supply of wastewater entering the reclamation process. This is usually in contrast to the irregular urban flows. Balancing inflows is normally accomplished through the use of maturation ponds.

Also, quality analysis is essential since each reuse application has its own quality requirements. Specific approaches to reclamation technologies vary depending on the quality of the wastewater. This, in turn, dictates the specific operation and maintenance requirements for each approach. It is essential to the proper operation and maintenance of these systems that the correct procedures be adopted. Regular and frequent monitoring is required for the safe use of this technology, including flow measurement, continuous monitoring of selected parameters, sampling for quality control, maintenance of instrumentation and operating systems, and visual observation and bio-monitoring of the product water.

Conventional System

The simple conventional system is described here, although this could be operated as activated sludge system.

Technical Description

The technology consists of

(i) the preliminary treatment stage which has a screen chamber, a grit chamber and flow recorders similar to the waste stabilization system;

(ii) primary sedimentation basins for me settlement of organic solids;

(iii) biological reactors which in Africa are commonly trickling filters for the biodegradation of soluble organics;

(iv) secondary sedimentation basins for settlement of biomass;

(v) sludge treatment systems such as digesters or drying beds.

Extent of Use

The technology is widely used in Africa.

Operation and Maintenance

Maintenance consists primarily of inspecting and repairing pumping systems and screens, and sludge removal.

Level of Involvement

These systems may be constructed by local artisans, but designed by engineers.

Costs

Costs are relatively high compared to ponds.

Suitability

This technology is suitable in all countries, but for reasonably large settlements.

Effectiveness

The technology is effective in removal of BOD.

Environmental Benefits

The use of this technology usually improves the water quality of the discharged wastes but can potentially result in nutrient enrichment of surface and groundwater.

Advantages

The technology is effective in removal of BOD5.

Disadvantages

This technology needs skilled manpower to operate, is costly to run, and does not remove nutrients leading to potential pollution problems.

Cultural Acceptability

Poor operation results in odour problems which are objectionable to community. Also, Africans are not usually at ease with seeing their own excreta.

Information Sources

Standard text books and research organizations in Africa

Level of Involvement

The major player is the wastewater collection and treatment agency, normally the local authority. The user receiving secondary effluent becomes responsible for its tertiary treatment, even though he would have to depend on the local authorities for the implementation of the necessary catchment quality control.

Costs

Costs vary from moderate to very high depending on method. Major factors are the capital costs of treatment facilities; labour, spares and energy; reticulation systems; and land. In Bulawayo, Zimbabwe, the costs of sewage treatment using coagulation, clarification, rapid sand filtration and chlorination stages is about $0.05/m3

Effectiveness of the Technology

The group of technologies is extremely effective as for each unit of wastewater recycled an equivalent amount of freshwater is saved.

Suitability

This technology is appropriate in regions experiencing severe water shortages, and where wastewater is collected in a sewerage system. Direct recycling is most appropriate for use in towns with modified activated sludge (MAS) plants since these plants have the capacity to remove nutrients. However, effluent used for irrigation need not undergo MAS treatment since the nutrients a beneficial for plant growth.

Modified Activated Sludge (MAS) System

The MAS system is a wastewater treatment system aimed at polishing the effluent to remove nitrates and phosphates which can contribute to eutrophication of surface waters.

Technical Description

The MAS system has a preliminary stage similar to conventional wastewater treatment systems, including the primary sedimentation process. MAS treatment involves me passage of settled wastewater through a series of anoxic and oxic zones, la die oxic zone, nitrification of ammonia nitrogen compounds take place, and, in the oxic zone, the redaction of nitrates take place. Microorganisms in both zones utilize soluble phosphorus for biomass production (growth). The excess biomass thereby generated is settled in the sedimentation basin. Oxygen in oxic zone is provided by electrically drive aerators. The effluent produced in this way can be discharged to a receiving water body with low dilution potential, and in situations where effluent from conventional systems would result in nutrient enrichment of the water body.

Extent of Use

MAS systems are used in South Africa, Zimbabwe, and Namibia, and are being used experimentally in other countries.

Operation and Maintenance

Electric motors and rotors need regular inspection. All other operation and maintenance requirements for conventional wastewater treatment plants apply.

Level of Involvement

Use of this technology requires skilled operators and support staff.

Costs

MAS systems are expensive to operate, especially given the electric power input required.

Suitability

The technology is suitable for urban centres that need to, or may need in future to, recycle water.

Effectiveness of die Technology

The technology is very effective in removal of BOD, suspended solids and nutrients

Environmental Benefits

MAS treatment reduces the dangers of pollution of surface water bodies.

Advantages

MAS treatment removes nutrients, and produces a product water that may be recycled immediately.

Disadvantages

The technology requires high energy inputs, making it expensive to operate.

Cultural Acceptability

There are no known cultural problems recorded for the specific technique of nutrient removal, but communities object to having a wastewater treatment plant close to residential areas. There are religious restrictions on direct reuse of wastes.

Information Sources

City Engineer, City of Harare, Zimbabwe.
City Engineer, City of Pretoria, South Africa.
Design details may be found in standard wastewater engineering textbooks.

Environmental Benefits

Poor or absent control of effluent quality can have serious health problems for the users. However, most countries using this technology have both water quality and public health standards in place. Use of wastewater for irrigation can enhance crop or plant production and improve surface water quality.

Advantages

It is a proven technology that is effective in water resources management. Costs and production efficiencies are predictable. Moderate skill levels are required. Use of this technology typically reduces pollution problems by turning wastewater into an economically attractive substitute water source for irrigation and non-potable industrial use at reasonable cost. It therefore increases water availability.

Disadvantages

Wastewater reuse may be culturally and aesthetically unacceptable. Increased nutrient loads may lead to enhanced algal growth in surface waters and the need for higher rates of chemical usage in water treatment. There is also a possibility of ground water pollution. As noted above, health problems can occur if the effluent has been poorly treated. Poor or incomplete treatment can also lead to a risk of contamination of potable water with heavy metals and organic compounds. Because salts are not significantly affected by these treatment techniques, there is the risk of gradual build up of proportions of dissolved salts to unacceptable levels with direct reuse.

Cultural Acceptability

The acceptability of this technology depends on the region. Some cultures do not accept the handling and direct reuse of wastewater. It is essential to determine an appropriate balance between cost and efficiency.

Further Development of the Technology

There is a need for legislation and regulations for the control of both treatment and use, where these do not exist, and, where they do, for their consistent application. Studies need to be undertaken to determine the variations in effluent quality and its effect on the raw water being reused.

Information Sources

Odendaal, P.E. 1991. Wastewater reclamation technologies and monitoring techniques. Water Science and Technology, 24(9): 173-184.

Odendaal, P.E. and L.R.J. Van Vuuren 1979. Reuse of wastewater in South Africa - Research and application. Proceedings of the Water Reuse Symposium I, 25-30 March 1979, Washington, DC. p. 886-906.

Department of Water Affairs 1986. Management of the Water Resources of the Republic of South Africa, Government Printer, Pretoria.

Holland, J.R. and S.M. Holland 1994. Urban Water Supplies Conservation Study for MLGRUD. Emergency drought recovery and mitigation programme.

Binnie and Partners Consulting Engineers, in association with Burrow Binnie Limited 1993. Bulawayo, Water Conservation Study, Final Report. Vol. 2. Overseas Development Agency, London.

Meiring, P.G.J., P. Rose, and O. Shipin 1994. Algal aid puts a sparkle on effluent. Water Quality International, 1994(2): 30-32.

Meiring, P.G.J., R.J.L.C. Drews, H. Van Eck, and G. Stander 1968. A guide to the use of pond systems in South Africa for the purification of raw and partially treated sewage. National Institute for Water Research, CSIR, Pretoria.

2.3.2 Indirect reuse

Technical Description

Indirect reuse is the process whereby effluents from treatment plants are discharged through a secondary polishing process before the water is abstracted elsewhere. Such polishing regimes may be in an underground mine, across a dispersion field, via a river, or through some similar, intermediate step between the point of effluent discharge and raw water abstraction. The polished water may be mined using boreholes, after being discharged to surface water courses or to aquifers for subsequent abstraction, as in the case of heated effluent from some power station cooling plants.

Extent of Use

Indirect reuse is widespread in Botswana, Zimbabwe, South Africa and Malawi.

Operation and Maintenance

Quality control of effluent is necessary to ensure that it meets the desired standard. The standards should be set so that the effluent receives the appropriate degree of treatment prior to the treated effluent being abstracted for further use. In this regard, poor monitoring of receiving water body quality is a major concern in a number of countries in Africa.

Where pumping of effluent is required, pump spares may be a problem since these are usually imported in most cases.

Level of Involvement

Use of this technology involves the employment of skilled technical personnel, especially in the conduct of the quality assurance practices.

Costs

Transfer techniques used to move the effluent from the treatment plant to the receiving polishing regime largely determines the cost. If transfer can be accomplished using gravity flows, costs are significantly less than if pumping is required. These costs are added to the cost of the conventional treatment stage.

Effectiveness of the Technology

This technology can be effective in polishing treated wastewater for reuse. The transfer of the treated wastewater from the treatment plant to the polishing regime is usually highly efficient, but recovery of the discharged water is problematical, depending on the nature of the polishing regime. Recovery of water from surface polishing regimes may be greater than recovery from underground regimes.

Suitability

The technology is suitable for use in all countries in Africa where appropriate conditions for transfer and polishing exist.

Environmental Benefits

While this technology can augment conventional water sources, the possibility of polluting both surface and ground waters is high.

Advantages

It is a proven technology that is effective in water resources management. Costs and production efficiencies are generally predictable, and use of the technology can reduce water pollution problems. Moderate skill levels required, particularly in quality control. Because the wastewater generated is economically attractive for irrigation, this technology can increase water availability.

Disadvantages

The discharges associated with this technology may be culturally and aesthetically unacceptable. Increased nutrient loads demand the increased use of chemicals in raw water treatment. There is also a risk of contamination of potable water with heavy metals and organic compounds, and a possibility of surface and ground water pollution.

Cultural Acceptability

The acceptability of this technology depends on the region. Some cultures do not accept the handling and reuse of wastewater. However, the indirect nature of this technology may overcome such prohibitions on use of wastes.

Further Development of the Technology

Studies need to be undertaken to determine the variability of effluent quality and its effect on the raw water abstracted for reuse.

Information Sources

Odendaal, P.E. 1991. Wastewater reclamation technologies and monitoring techniques. Water Science and Technology, 24 (9):173-184.

Odendaal, P.E. and L.R.J. Van Vuuren 1979. Reuse of wastewater in South Africa - research and application. Proceedings of the Water Reuse Symposium I, 25-30 March 1979, Washington DC. p 886-906.

Holland, J.R. and S.M. Holland 1994. Urban Water Supplies Conservation Study for MLGRUD. Emergency drought recovery and mitigation programme.

Binnie and Partners Consulting Engineers, in association with Burrow Binnie Limited 1993. Bulawayo, Water Conservation Study, Final Report Vol. 2. Overseas Development Agency, London.

Meiring, P.G.J., P. Rose, and O. Shipin 1994. Algal aid puts a sparkle on effluent. Water Quality International, 1994 (2):30-32.

Meiring, P.G.D, R.J.L.C. Drews, H. Van Eck, and G. Stander 1968. A guide to the use of pond systems in South Africa for the purification of raw and partially treated sewage. National Institute for Water Research, CSIR, Pretoria.

2.3.3 Regeneration water

Technical Description

Use of regeneration water involves the indirect reuse of water that has already been used, primarily in the agricultural sector. In some instances, this water is utilised for urban purposes. The objective of this technology is to augment the available water through reuse.

In irrigation, excess irrigation water applied to the land surface drains via subsurface drains to open channels where it is conveyed away from the fields to prevent waterlogging of the crop roots. Traditionally, such water is discharged to the nearest surface water course, where it is effectively removed from the irrigation system. In contrast, this technology conveys the drainage water to collection areas where it is pumped into reservoirs, mixed with fresh water and reused for irrigation.

Extent of Use

In Zimbabwe, use of regeneration water is currently practised on the sugar estates of Hippo Valley, Chiredzi and Triangle, and in other agricultural areas. For example, the Town of Glendale, Zimbabwe, depends for its water supply on regeneration water emanating from the irrigation of large citrus plantations in the Mazowe Valley.

Operation and Maintenance

Regular inspection, repair and maintenance of pumps and accessories is required.

Level of Involvement

Depending on the scale of the irrigation operations, government, large and small farmers, and other institutions may make use of this technology.

Costs

For irrigation purposes the major cost is pumping. The amounts of money involved depend on the size of the pumps, which, in turn, is dependent on how much water is available. Therefore, cost of this technology is very much a function of the size of irrigation operation. Irrigation pump installation costs in Zimbabwe are about $2000/ha.

Effectiveness of the Technology

Water from the drains is put to use instead of being “wasted”. Additional water for irrigation is made available. With flood irrigation, water collected in the drains accumulates at as much as 31/s from a 400 ha section. This water is enough to irrigate an additional 3 ha of cropland. In the case of Glendale, the water requirements of the small town, 321/s, are more than covered by the volume of regeneration water recovered through this technology.

Suitability

This technology is appropriate wherever water shortages are experienced. The use of regeneration water may not be appropriate where the regeneration water has a high concentration of dissolved salts.

Advantages

Additional water is made available for many other purposes through the use of this technology. Extra hectares may also be cropped as a result.

Disadvantages

Regeneration water has been found to be extremely saline, having electrical conductivity values greater than 4 million mS/cm at 25°C, in some situations. This leads to salinity problems where applications of regeneration water are of high volume and/or prolonged. In cases where the regeneration water is utilised in the area where it is generated, there are usually some increased costs due to the extra pumping required to lift the regenerated water to the head of the irrigation scheme.

Cultural Acceptability

No cultural problems relating to the use of this technology have been recorded.

Information Sources

Hippo Valley Estates, Post Office Box 1, Chiredzi, Zimbabwe, tel. 263-96-2381, fax: 263-96-2554.

Triangle Limited, Private Bag 801, Triangle, Zimbabwe, tel. 263-96-6221, fax: 263-96-6513.

2.4.1 Urban water conservation

Technical Description

The techniques included in this option take various forms and include the following water conservation measures which may be implemented by local authorities:

(a) The development of an appropriate tariff policy:

Under this approach, tariffs are levied as steep progressive rates, which subsidize the very poor and may also offer special rates for the promotion of industry. However, cost recovery is essential in order to ensure a sustainable operation, and pricing levels should be such so as to guard against water wastage.

(b) The metering of individual stands and flats:

The metering of individual properties puts the burden for water conservation on the consumer, which is the most effective means of ensuring urban water conservation.

(c) The institution of efficient meter reading and billing mechanisms:

Well-maintained and working meters, read accurately and regularly, and followed-up by efficient billing procedures ensure that consumers do not abuse municipal water supplies. Monitoring of such systems for changes in rates of consumption and rates of return or payment of bills provides accurate data for planning purposes. Relating consumption paid for to the amount of water produced provides a check on unaccounted for water and can alert the water utility of leakages or breaks in the supply system.

(d) The use of water-saving fittings:

By using water-efficient fittings such as low flush toilets, low-volume shower heads and taps, and flow limiters, consumers can achieve the same degree of benefit from a lesser volume of water.

Extent of Use

Water conservation approaches have met with varied responses in the African region:

a) Development of appropriate tariff structures is generally a weak area in most countries in Africa. While some form of tariff structure exists in all of the countries of Africa, those that have attempted to set economic tariffs still fail to separate the water account from the rest of the municipal (general) expenditure account, which typically negates the benefit to the water utility of setting economic tariffs. (Such benefits, include the availability of finances to update or expand their production and distribution networks; by considering water revenues as general revenues, the water utilities are forced to compete for funds with all other municipal services.) For this reason, privatization of water services is being encouraged in a number of African countries.

b) Although metering is encouraged in most countries of Africa, not all consumers are metered appropriately. Bulk supplies and stand posts are common in the rural areas, while, in large cities, only the affluent urban areas are typically metered.

c) Billing mechanisms are in place in most countries of Africa, but these are not properly monitored. Lack of monitoring of payments significantly reduces the recovery rate for monies invested in water treatment and distribution. Unaccounted for water, including illegal connections, accounts for up to 30% of potable water generated in most countries. Likewise, lack of monitoring and efficient bill collection generally means that development of water distribution systems lags well behind the rate of urbanisation.

d) Water saving fittings are being promoted in the dry countries of Africa, especially in Southern Africa.

Operation and Maintenance

The techniques described above are largely social strategies aimed at conserving water. Additional actions may be needed to operationalise these strategies. The following operation and maintenance techniques may be applied by water utilities when implementing water conservation measures:

a) Pressure and flow control:

Municipal water distribution systems normally have different ages. The tendency to leak is highest within the older portions of the network. To minimize leakages, it is essential that these different regions are zoned, and supply pressures be varied accordingly. Scheduled maintenance and leak detection systems are essential.

b) Consumer information programming and conservation promotion:

Conservation is promoted through the formulation of rules and regulations for promoting efficient use of water and minimizing wastage, and by effectively informing consumers of measures to reduce wastage of water.

c) Distribution system maintenance:

Corroding pipes cause leakage. Replacement of corroded pipes with non-perishable pipes, such as PVC piping, reduces water losses through leaks and ensures insofar as possible an uninterrupted supply to consumers. Regular maintenance reduces the risk of service interruptions due to breaks in the supply lines.

d) Monitoring and policing in cases of misappropriation, theft and fraud:

Replacement of faulty meters, training of meter readers, and efficient administrative oversight can detect and reduce illegal connections to distribution systems, thereby protecting the revenues of the water utility and reducing losses within the distribution system. For efficient operation and administration, it is essential that the network be divided into district meter zones and that an accurate and up-to-date map of the distribution system is made and maintained.

Level of Involvement

The urban authority is usually the major player in promoting water conservation. However, Government agencies as in some municipal areas may be the single largest consumer of water and should be enlisted to support the water conservation promotion program. Civic organisations and NGOs can also play a role in consumer information programming.

Costs

The costs vary depending on the measures taken, but more efficient use of water reduces or delays need for expenditure on new water supplies while ensuring that revenues are available for this purpose. Informational programming costs are minimal, especially if combined with other informational programming, such as school curricula in environmental sciences, health awareness campaigns or similar on-going activities, while provision of water-saving hardware to replace conventional plumbing supplies may be more costly. Manpower costs to improve distribution system maintenance and management are also relatively high but are typically offset by the increased revenue generated from these actions.

Effectiveness of the Technology

With effective leak detection and pipeline repair programmes in place, it has been categorically shown that the real savings far exceed the costs. For example, low volume flush toilet cisterns can reduce the volume per flush from 15 to 8 litres.

Suitability

Use of water conservation techniques is appropriate in all countries.

Advantages

Use of these techniques can result in saved water that can be put to other uses. There is a significant reduction in costs, and an increase in water utilization efficiency (and revenues). Capital projects for the construction of new water reservoirs may be deferred to a latter date, or capital made available for expanding the distribution system to meet new demands.

Disadvantages

Some expenditure is necessary to put a water conservation programme into action. Once the system is in place, use of water saving fittings may reduce wastewater flows to below the design flows for older trunk sewers and can sometimes result in blockages, necessitating a system redesign and retrofit. While the cost of such actions may be offset to a degree by increased revenues generated by charging consumers an economic rate for water, services charged at economic rates may be too expensive for the poorest segment of the community to afford, requiring additional arrangements to minimise illegal connections to the system.

Cultural Acceptability

No cultural problems have been noted, although the societal implications of charging economic rates for water should be recognised and accommodated in an equitable manner.

Further Development of the Technology

There is need to undertake studies to correlate soil resistivity with leak occurrence in, especially, steel water mains, taking into account pipe age and technical specifications. Research is also necessary to determine the most appropriate management systems required for water conservation in Africa. In cases where low volume fittings are adopted, it is necessary to consider their impact on trunk sewer slopes and reduced flows.

Information Sources

Contacts

Castle Brass Holdings (Pty) Ltd., Post Office Box 4082, Luipaaardsvlei 1743, South Africa.

City Engineer's Department, Post Office Box 4323, Johannesburg 2000, South Africa.

Bibliography

American Waterworks Association s.d. Water Conservation Management. Washington, DC.

City Engineer's Department 1989. Water Loss Analysis on Municipal Distribution Systems. Water Research Commission Report No. 157/1/89, Pretoria.

Holland, J.R. and S.M. Holland 1994. Urban Water Supplies Conservation Study for MLGRUD. Emergency drought recovery and mitigation programme.

National Building Research Institute 1986. Water Economy Measures. Guidelines for Local Authorities. Water Research Commission, Pretoria.

Jeffcoate, P. and A. Saravanapavan 1987. Working Guidelines for the Reduction and Control of Unaccounted For Water, World Bank Technical Paper No. 72, Water Supply Operations Management Series, Washington, DC.