Investigation Of Hydroelectric Generation Options In Addis Ababa City Municipal Wastewater Treatment Plants

Energy recovery through local hydropower generation is a way of coping with high electricity expendituresrnin wastewater systems (WWS). There are some hydropower units operating in wastewater treatment plants,rnshowing that there is an interest for this type of small-hydro, but there is still a lack of awareness of itsrnpotential. This study assess the hydroelectric potential in the existing wastewater treatment plants in AddisrnAbaba city, by introducing energy recovery turbines (pump as a turbine) on the downstream side ofrnwastewater treatment plants. rnIn wastewater treatment plants especially the electro-mechanical equipment consumes a considerablernamount of energy in the treatment process. Specially, the newly constructed WWTP in Addis Ababa arerntotally dependent on electricity to function. Hence, by introducing a wide range of “pump as turbine”rnconfigurations that can offer cost-effective means of generating energy decentrally at heads from 2.5 to 300rnmeters and rates of flow ranging from 10 to 5000 liters per second, it is possible to recover the wastedrnpotential. rnIn this study, industrial centrifugal pump running as turbine were analyzed using Ansys cfx computationalrnfluid dynamics (CFD) software. The pump was simulated in direct and reverse modes and completerncharacteristic curves of the pump in direct and reverse modes were obtained. rnThe model was built up, starting from the real geometry, with a commercial tridimensional code, which isrnparticularly suitable to simulate pumps. The numerical model was simulated. First, the model results wererncompared with the data declared by the pump manufacturer and the simulation model showed goodrnaccuracy. Then after using the validated model, the reverse mode was analyzed. The boundary conditionsrnwere changed in order to running the pump as a turbine. The results that were obtained from the simulationrnof pump in turbine mode is compared with the result obtained from Chapallaz design method. The resultsrnshowed good accuracy. During the analysis the selected site has power production capacity between 4.1147rnkWrndepending onrnthernsiternconditions.rnFinally a relationship between flow, head and power was developed and sites with flow rate of above 40,000rnmrn3rn/day and head above 25m will be economically feasible sites for hydro-power generation in wastewaterrntreatment plants.

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