ABSTRACT
This study investigates the settling characteristics of the raw water of Kubanni Dam at the main campus of Ahmadu Bello University, Zaria. The investigation included plain sedimentation and sedimentation of coagulated water samples using aluminium sulphate (alum) as coagulant. Coagulation and flocculation tests were performed by the batch method in beakers (Jar tests), while the sedimentation tests were performed using settling column. The results obtained indicate that plain sedimentation is not adequate for the turbidity removal from the raw water of the dam, but coagulation and flocculation processes are necessary, An optimum alum dose of 50mg/L is required to coagulate the water during the dry season and 70mg/L during the rainy season. An average turbidity removal of 85.596 was obtained from the sedimentation of the coagulated water samples as compared to 26% obtained from the plain sedimentation of the water samples. Data from the settling of the coagulated water samples are used to design new sedimentation basins and for up-grading the existing sedimentation basins of the University water works. Four rectangular tank units are suggested, each of dimensions 21m x 5.5m with effective depth of 3m. Also four circular tanks could be used each of diameter 12m and effective depth of 3m. Using the experimental data the existing four basins (square in plan- 8.5 x 8.5m and effective depth of 5m) are up-graded by - viadjusting the volumetric flow rate. Two additional basins are recommends to achieve turbidity removal of 85.5% instead of the 70% removal being achieved presently. The structural design of the basins and the estimated cost are also presented.