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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.

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