19.3.3  Centralised wastewater treatment systems

In larger towns and cities, liquid waste may be conveyed via a sewerage network to a centralised wastewater treatment plant; for example, Addis Ababa’s waste is treated at the Kality Wastewater Treatment Facility. Simple small-diameter sewers convey sullage and sewage from individual households to larger main sewers and then to the treatment plant. (Note that the word ‘sewerage’ refers to the network of pipes and ‘sewage’ refers to the liquid waste that flows through the sewers.) This method is not likely to be used in rural and peri-urban areas of Ethiopia. In addition to sewage, industrial waste may be discharged into the sewerage network – although it may have to have special treatment (technically called pre-treatment) onsite beforehand.