Water Treatment Plant Performance Evaluation Using Turbidity As A Parameter

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Addis Ababa University


Gafarsa and Lagadadi Water treatment plants play a vital role in supplying drinking water to Addis Ababa City since about 55 years. The two WTPs are located on opposite direction of the city. Groundwater sources developed at the southwest direction of the city augments the waters sources from the two treatment plants. This study focused on evaluation of performance efficiency of the two water treatment plants in view of turbidity removal. The evaluation was conducted by collecting primary turbidity data of water sample at outlet of clarifiers and filters where turbidity of water is removed. During rainy season due to high turbidity of raw water from the impounding reservoirs, daily production of the plants decrease as the surface loading rate is minimized to maintain the required water quality. Magnitude of floc carryover also increases during the wet periods. Lagadadi treatment plant is constructed in two stages. The second stage clarifiers are equipped with tube settlers while the first stage clarifiers have no any type of settlers installed. As observed from the turbidity removal efficiency evaluation of the two stages filters, the second stage filters are more efficient than that of the first stages. The study result revealed that turbidity removal efficiency of Lagadadi treatment plant filters is better than that of Gafarsa. The average turbidity removal efficiency of Gafarsa and Lagadadi filters are 53.13% and 88.45% respectively. For improving rainy season output of the water treatment plants, this study recommended construction of bank filtration adjacent to intake from the impounding reservoirs which reduces turbidity of the raw water by half. Non-uniformity is observed in orifice type weir of the two treatment plant clarifiers, which could be the most probable reason for floc carryover. For minimizing floc carryover, it is recommended to regularly clean the orifices inner surface to maintain uniformity of the cross sectional area which in turn regulate the flow velocity stabilizing the suspended flocs to settle.



Gafarsa and Lagadadi Water