1. Explain the importance of the settling tanks in the Waste Water Treatment Plants (WWTP) and discuss the factors affecting the efficiency of the settling process of particles in a slurry (Max. 400 words). All sources of information should be well cited using Harvard-Hull referencing style. [10 mark] 2. Calculate the settling velocity of the equivalent spheres and briefly describe the parameters that affect the settling velocity.

Given data Ut= 0.7 m/s and D= 0.3m

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A slurry made from hollow cylinder-shaped particles in water is required to be separated in a settling tank. In order to use the common equations describing slurries, we very often 'simulate' the non-regular shaped particles with equivalent spheres. The temperature of the slurry is 20C, and the volume of water is 32m3. The slurry contains the abovementioned equivalent spheres with a diameter of 225m. The volume of all particles in the slurry is 18m3. To be able to proceed with the design of a settling tank for the separation of the solids from the water you need to preliminary estimate the settling velocity of particles of the slurry. The terminal velocity of the particles (Ut) and tank diameter (D) are given in table 1 based on the Student Number. Assumptions: - The equivalent spheres have a uniform size. - The physical properties of water (density and dynamic viscosity) must be obtained from the literature/ online databases at the process temperature