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Sewage in the Eastern African Region

A serious threat to ecological health and economic prosperity

There is a direct relationship between population growth and waste generation. In the case of most large urban centres the solid waste and sewerage facilities have remained the same while the population has increased, leading to decline in percentage population served by the facilities. Only a small proportion of dwellings throughout many of the large urban centres of the mainland States are connected to a sewage system. The sewage which is collected is often pumped directly into coastal waters without any treatment.

The majority of the population in the region use septic tanks and pit latrines. There is large degree of uncertainty concerning the BOD and TSS loads that reach the water environment from on-site domestic-sewage disposal systems. Calculations using the rapid assessment estimate loads are based on the FAQ factor of 0.7/kg/head per day (WHO 1989). However, only a fraction of the BOD and solids actually reach the water environment depending on the efficacy of septic tanks/pit latrines and the local hydrogeological conditions. Such data should be treated with caution and only tentative interpretations will be made of the significance of its effects on the water environment.

There is an urgent need for monitoring of microbial contamination of ground waters in coastal areas of all States of the region to assess the scale of the problem.

As was the case for industrial effluents, the importance of the organic (BOD) load to coastal waters from domestic sewage cannot be assessed more completely without detailed data concerning the residence times and mixing rates in coastal areas.

Degradation of coastal habitats caused by the dumping of domestic and industrial waste in coastal areas, and its transport via near-shore waters, represents a serious threat to the ecological health, biological diversity of coastal habitats and, in the long term, the economic prosperity of commercial and artisanal fishing. Domestic waste also represents a hazard to public health when it is allowed to accumulate in urban areas.

The release of untreated domestic sewage has been associated with the occurrence of eutrophication in near-shore coastal waters, phytoplankton blooms and the subsequent degradation of coastal habitats and reduced fish catches. However, it is not possible to assess the scale of the problem without adequate monitoring data and detailed scientific research.