By Michel Rochon, Morrison Hershfield
Improving LivesWater & Wastewater Wastewater treatment systems
Addis Ababa, the capital and largest city of Ethiopia and headquarters of the African Union, is growing rapidly. In 2007 its population was approximately 3.5 million and most of this growth is due to in-migration. In the slum areas the...
Addis Ababa, the capital and largest city of Ethiopia and headquarters of the African Union, is growing rapidly. In 2007 its population was approximately 3.5 million and most of this growth is due to in-migration. In the slum areas the population density reaches 632 inhabitants per hectare.
As it moves to become a world-class economic centre, Addis Ababa is undergoing significant development. Water and wastewater infrastructure represents a top priority.
There are three sewer catchment areas, Kaliti, Eastern and Akaki. Kaliti, the largest basin that includes the core of the city, is similar to other burgeoning urban areas in Africa, and modernizing to 21st-century systems is a challenge.
At the same time the technological possibilities in Africa are exciting. For example, in the absence of a traditional landline telephone system, the continent has jumped this step and embraced the widespread use of wireless technology; more than 30 African nations have more cell phones than landlines. Water and wastewater infrastructure is experiencing a similar trend, benefiting from the most current developments around the world, and leaping from latrines and simple septic tank technology, to systems that could serve as a model for urban centres everywhere.
Poorer people use latrines
The Addis Ababa Water and Sewerage Authority recently awarded Morrison Hershfield a project, funded by the World Bank, to improve the sewage collection and treatment systems in Kaliti.
The existing piped sewer system serves only a small portion of the Kaliti catchment area. It has approximately 30 kilometres of trunk sewers and 320 kilometres of secondary sewers, with many sections suffering from under-capacity piping. Many of the residents of the area currently use septic tanks and pump-out technology. People in poorer areas are using latrines. With transportation and drainage infrastructure unable to meet the demand, and the density of development increasing, the quality of life in the community is dramatically reduced.
Morrison Hershfield’s project manager Doug McRae is in Edmonton. He explains: “The goal of our project is to establish widely available piped waste water services, which will be a large step towards improving the overall public health of the community. With the increased prosperity of the city, buildings of 6 to 10 storeys are springing up everywhere and the current sewage collection system just can’t accommodate them the way it is.”
The project includes reviewing the existing sewerage master plan and estimating water demand and the resulting sewage flows. Morrison Hershfield developed a model of the collection system showing the current piping and phased expansion to serve the entire Kaliti catchment area. The ultimate system will reach approximately 327 kilometres of trunk sewers when all the phases are complete.
New treatment plant will have sludge digestion
The current treatment process consists of a lagoon system sized to handle approximately 50,000 people, compared to an estimated 2.5 million people who currently reside in the basin. As the collection system is expanded, so the treatment system must expand also. Lagoons are no longer appropriate due to the large land area required, so the project will add a state-of-the-art wastewater treatment plant that will improve the quality of the discharged treated sewage effluent.
For the new facility Morrison Hershfield selected a process that is easy to operate and forgiving to the varying strength of the wastewater flows. The process employs screening and grit removal, primary clarification, a trickling filter, secondary clarification and polishing ponds.
The feasibility of using the treated effluent as a source of irrigation water is also being explored. This feature would provide the local farmers with a water source considerably cleaner than is currently found in the adjacent Little Akaki River.
The treatment system will feature sludge digestion that will allow the city to capture the resulting biogas for energy production and will reduce the plant’s carbon footprint. Electrical energy is a critical issue due to the growth of the city and the electrical energy produced from biogas will help supply some of the plant’s needs.
Morrison Hershfield has partnered with the Ethiopian engineering firm ARMA who will provide local engineering and technical support. With McRae as project manager, Alemeshet Tsegaye of ARMA is the deputy (local) project manager. Tadesse Lemu, P.Eng. and Miressa Fola, P.Eng. of Morrison Hershfield, both originally from Ethiopia, are lead engineers.
“We are pleased to have a role in ensuring adequate and safe sanitation facilities for the people of Addis Ababa,” says McRae. ccE
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