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Newsletter and Technical Publications

<Sourcebook of Alternative Technologies for Freshwater Augumentation in Africa>

2.3 WASTEWATER TREATMENT TECHNOLOGY AND REUSE

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.

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