Investigation of Hydroelectric Generation Options in Addis Ababa city municipal Wastewater Treatment Plants

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Addis Ababa University


Energy recovery through local hydropower generation is a way of coping with high electricity expenditures in wastewater systems (WWS). There are some hydropower units operating in wastewater treatment plants, showing that there is an interest for this type of small-hydro, but there is still a lack of awareness of its potential. This study assess the hydroelectric potential in the existing wastewater treatment plants in Addis Ababa city, by introducing energy recovery turbines (pump as a turbine) on the downstream side of wastewater treatment plants. In wastewater treatment plants especially the electro-mechanical equipment consumes a considerable amount of energy in the treatment process. Specially, the newly constructed WWTP in Addis Ababa are totally dependent on electricity to function. Hence, by introducing a wide range of “pump as turbine” configurations that can offer cost-effective means of generating energy decentrally at heads from 2.5 to 300 meters and rates of flow ranging from 10 to 5000 liters per second, it is possible to recover the wasted potential. In this study, industrial centrifugal pump running as turbine were analyzed using Ansys cfx computational fluid dynamics (CFD) software. The pump was simulated in direct and reverse modes and complete characteristic curves of the pump in direct and reverse modes were obtained. The model was built up, starting from the real geometry, with a commercial tridimensional code, which is particularly suitable to simulate pumps. The numerical model was simulated. First, the model results were compared with the data declared by the pump manufacturer and the simulation model showed good accuracy. Then after using the validated model, the reverse mode was analyzed. The boundary conditions were changed in order to running the pump as a turbine. The results that were obtained from the simulation of pump in turbine mode is compared with the result obtained from Chapallaz design method. The results showed good accuracy. During the analysis the selected site has power production capacity between 4.1147 kW depending on the site conditions. Finally a relationship between flow, head and power was developed and sites with flow rate of above 40,000 m 3 /day and head above 25m will be economically feasible sites for hydro-power generation in wastewater treatment plants.



municipal Wastewater Treatment Plants, Hydroelectric Generation, Addis Ababa