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1.3 WASTEWATER TREATMENT TECHNOLOGIES AND REUSE
1.3.1 Wastewater Reuse
Wastewater from a conventional or wastewater stabilization pond
system is directed by a system of pipes or canals to a night storage
reservoir from which it is used for pasture or crop irrigation. The crop
will strip the wastewater of its excess nutrients (nitrates and
phosphates), while many pathogens that may be in the wastewater die due to
the inhospitable environment at the soil surface or are filtered out by
the vegetation. Nevertheless, the ability of some pathogens to survive
suggests that this technology be applied cautiously, with full knowledge
of the characteristics of the wastewater source being used. Appropriate
infrastructure is required to transport the effluent from wastewater
treatment works to the site of use.
This technology may be combined with aquacultural operations. In which
case, ponds may need to be designed for use in fish culture and additional
infrastructure will be needed for this purpose. If the effluent is to be
applied for irrigation of crops and the production of foodstuffs, special
pre-treatment steps may need to be applied prior to the transportation of
the effluent to the storage site.
Extent of Use
Wastewater reuse is practised in Tunisia, South Africa, Zimbabwe, and
Burkina Faso. Over 15 schemes are operational in Tunisia. In Tunis, for
example, irrigation of citrus trees with wastewater has been done since
1964. There are plans to extend the wastewater irrigation scheme to an
additional 40 000 ha around Tunis.
Operation and Maintenance
The treatment system that provides the wastewater is usually maintained
by the local authority. The conveyance system and wastewater distribution
system may be operated by these same local authorities, but is generally
operated by governmental agricultural development authorities from the
point of effluent discharge to the end user. The on-farm distribution
system is typically operated by the individual farmers. Maintenance of the
pumping systems, delivery canals, pipes and furrows is required. It is
recommended that a system for monitoring the health of workers be
established to minimise the risk of spreading disease, given the nature of
the raw water.
Level of Involvement
The transfer system from the treatment works to the farmer is usually
managed by trained or experienced personnel from the local authority. The
application of the effluent onto the lands is done by the farmer, and does
not require a lot of technical know-how since it mimics traditional or
conventional practises. However, additional health precautions should be
used, and rural health workers should participate in training schemes
established to promote this technology. It is also important for the
farmers to know the application rates of the effluents to minimise the
occurrence of phosphorus poisoning of grazing animals and avoid
over-fertilisation. Thus, agricultural extension workers also should
participate in the establishment of this technology.
In Tunisia, wastewater is distributed to farmers by the local
Agricultural Development Authorities, which are responsible to the
Ministry of Agriculture. These Authorities construct and maintain the
wastewater distribution system. They distribute the wastewater to the
farmers according to an organised delivery schedule and collect revenues
from the sale of the wastewaters. The farmers are responsible for on-farm
In Tunisia, the cost to the farmer is $0.031/m3 of wastewater supplied.
Costs are influenced by the necessity of pumping, provision of
infrastructure for pipelines, distance from the source to point of
application, and type of application.
Effectiveness of the Technology
Irrigated agriculture benefits from the high nutrient levels present in
wastewater, thus reducing the need for fertilizer applications. In
aquacultural operations, reported yields of 0.8 to 4.0 tonnes/ha/year of
fish have been achieved from effluent ponds.
This technology is suitable wherever proximity to a wastewater disposal
system coincides with a need for irrigation water or where the nutrient
content can beneficially replace fertilisers or fish food. Applications of
wastewater in agriculture should conform to World Health Organisation
The reuse of wastewater reduces the need to further exploit available
freshwater resources which may be limited. There is, however, a danger of
polluting the environment, especially the groundwater, if the wastewater
is not properly treated initially.
Use of wastewater for agricultural purposes does not require special
skills, and can reduce the amount and use of other artificial fertilizers.
Wastewater reuse serves as a polishing ground for the removal of
nutrients, providing those nutrients to farmers at low cost. This
technology may offer job opportunities to farmers who cannot afford
conventional irrigation systems.
Wastewater reuse can cause pollution of surface and ground waters if not
properly managed. Further, the effluent may contain pathogens which can be
harmful to farmers and consumers of edible crops irrigated with
wastewater. Use of this technology requires significant investment in
effluent transfer mechanisms such as pumps and pipes. The availability of
irrigable land often limits the volume of wastewater that can be treated;
however, in some cases, the volume of wastewater may limit the extent of
A general social aversion to close association with excreta makes the
use of wastewater problematic in Africa. Fish from sewage ponds are too
closely associated with the excreta to be acceptable in many cultures.
However, irrigated crops may be fully acceptable. Religious, especially
Islamic, restrictions may also further limit the application of wastewater
reuse technologies in parts of Africa.
Further Development of the Technology
There is need for further promotion of this technology. However, the
bacteriological quality of the crops requires further investigation to
ensure the public health. The technology, although relevant and quite
widespread, is now being challenged by forthcoming technologies which seek
to remove nutrients from effluents and therefore recycle wastewaters
directly back to receiving waterbodies.
Centre Regional Pour l'Assainissement a Faible Cout (CREPA),
03 BP 7112, Ouagadougou 03, Burkina Faso, tel (226) 310359/60, fax: (226)
Ecole Inter-Etats d'Ingenieurs, de I'Equipment Rural (EIER),
BP 7023 Ouagadougou, Burkina Faso.
Edwards, P. 1992. Reuse of Human Wastes in Aquaculture. A Technical
Review. World Bank, Water and Sanitation Report No. 2.
Mara, D. and S. Cairncross 1987. Wastewater and Excreta Use in
Agriculture and Aquaculture in Developing Countries. UNEP/WHO, Geneva.
Tournakara Mistandia, C.T. and C. Toure 1994. Wastewater Reuse for
Irrigation; Studies of the Fertilizing Qualities of Treated Wastewater for
a Stabilization Pond Treatment Plant in Climate Sahelian Conditions. Proceedings
of the HYDROTOP 94 Conference, Marseille.