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2.3.2 Indirect Reuse
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
Extent of Use
Indirect reuse is widespread in Botswana, Zimbabwe, South Africa and
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
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.
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.
The technology is suitable for use in all countries in Africa where
appropriate conditions for transfer and polishing exist.
While this technology can augment conventional water sources, the
possibility of polluting both surface and ground waters is high.
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.
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.
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
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.
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
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.