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Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>

1.4 Reuse (Topic d)

Wastewater and stormwater represent resources that are often not used, or only considered partly because of lack of information about their benefits. Fear of possible health risks, cultural bias, lack of a method to analyse the economics of reuse projects comprehensively account for this neglect. Negative experiences with wastewater reuse in areas where it is practised under uncontrolled conditions have also scared away many prospective adopters of reuse.

Wastewater reuse particularly in agriculture requires consideration of the health impact, agricultural productivity, economic feasibility and socio-cultural aspects, and is therefore a multidisciplinary project. The professionals might represent public health, sanitary, engineering, agronomy, irrigation engineering, finance and economics as well as behaviour sciences.

Agriculture is usually the principal water user in developing countries of the region (about 75-80% of total water use), followed by industry, consumer and domestic use. In several semi-arid areas of Africa water allocation is critical, and recycling of wastewater is a high priority not only for irrigated agriculture in peri-urban lands growing high-value crops, but even for the so-called lower-priority domestic and industrial use (as in Namibia). In these dry zones, wastewater may constitute 25-75% of available irrigation water. Examples include Angola, Namibia, Botswana, and Zimbabwe.

1.4.1 Djibouti

A sanitation master plan was completed in 1988 for Djibouti with the financial support of African Development Bank (ADB) (see Section 1.3.1). The plan involves construction of 8.3 km of main collector, a lift station, expansion of the treatment plant, and rehabilitation of the existing network. It includes plans for production of orchards and market gardening by using the products of treated wastewater for irrigation in a peri-urban farming area of 25 ha.

1.4.2 Wastewater reuse is advanced in Zimbabwe

Industrial wastewater is separated from domestic wastewater before the latter is treated. The Scandinavian Sponsor for Semi-arid Regions (water short regions) has been a keen sponsor of the water conservation project in a number of water short South African countries. The Ministries of Water Affairs and Forestry and Development in the respective countries and the water section of the regional organization, SADC based in Lesotho are the implementing agencies.

1.4.3 Reuse in South Africa and Tunisia

Table 1.15 shows the proportion of total sewage reused particularly for agricultural purposes in South Africa and Tunisia. As much as 75% was recycled in the arid environment of Tunis. There are few other reports of the cultivation of fish in sewage fed aquaculture in Africa.

Table 1.15: Reuse of wastewater in Africa
Country
Volume Reused M3/yr
% of Total Sewage
Total Irrigation(%)
Remarks
South Africa (national) 70 16  - 1988
Tunisia (Urban Tunis) 68 75  - 1987
Source: Khouri et al. (1994)

1.4.4 Fish cultivation in sewage ponds in some African countries

Edwards (1992) reported on small scale operations in Kenya (Thika), Malawi (Dwangwa sugar estate), South Africa (Durban), and Zimbabwe. Fish, particularly tilapia is cultivated in sewage maturation and stabilization ponds. Reported fish yields are 4-5 tons/ha/growth period for the systems in Malawi, but only 0.8-1.2 tons/ha/year in Durban, South Africa.

1.4.5 Use of reclaimed wastewater in Namibia

South West Africa/Namibia is severely affected by water scarcity. Reclaimed water was introduced in Windhoek, the capital in 1969 to overcome the effects of a serious water shortage as a result of prolonged drought (see Section 1.3.1)

The percentage of reclaimed water in the blend with raw water sometimes was as much as 50% reclaimed water for short periods of less than 3 weeks during critical conditions. Average exposure to reclaimed water over the period of 17 years was 4.7% (i.e. some 292 days).

Since 1970s quality control studies have indicated that the product of the reclamation plant was of good quality and conformed to generally accepted drinking water criteria (Isaacson et al. 1987)

1.4.6 Effluent reuse as a supplement to water resources in Botswana

Average water demand for Gaborone by 2010 is estimated to be 63,000 m3/day with a wastewater generation of 57,180 m3/day. This represents a return factor to sewers of 90%, an optimistic estimate predicated on certain assumption concerning treatment technology, and perhaps climate, as the present ratio is of the order of 65% or less (Table 1.16).

Table 1.16: Botswana’s wastewater resources
Town Return flow in thousands m3/day (estimated)
  1990 2020
Gaborone 14.4 103
Francistown 5.0 38
Selebi Phikwe 4.4 21
Lobaste 3.2 8.2
Waneng  
1.3
4.0
Source: UN DESD (1996)

 These are resources that can be obtained within the borders of Botswana and at no extra cost to the government. In the light of erratic rainfall aggravated by long drought episodes (five years is not uncommon), it is prudent to maximize wastewater reuse. Established and possible uses of wastewater in Botswana include:

  • Peri-urban farming around Gaborone to meet high demand by farmers;

  • Demand by present and future industries;

  • Demand for landscaping by Gaborone City Council

  • Meeting water quality requirements for Water Utilities Corporation (WUC) for blending and treatment for potable use

  • Provision of water demanded by the Ministry of Agriculture (MOA) for extensive agricultural research projects at Seble College.

1.4.7 Cape Town, South Africa

In Cape Town, South Africa, a variety of stakeholders have succeeded in integrating environmental concerns into larger planning exercises. In addressing the metropolitan spatial framework, a number of green and brown environmental issues, open space creation, resource use efficiency, and urban watershed management are also addressed at the same time. Win-win solutions such as recycling of organic wastes to provide compost for urban and peri-urban agriculture are found. Such agriculture typically provides a subsistence for a significant proportion of the city’s food supply and jobs for the urban poor.

Except perhaps in Namibia and Zambia and South Africa, wastewater reuse is still in its infancy in Africa. The problems of accomplishing adequate treatment and cultural bias have militated against an effective use of this valuable resource, especially in the humid zones of the region.

 

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