Answer Happy

24 Re (a) Explain the derivation of the equation for particle settling velocity with the aid of figure illustration. Assume laminar flow condition (C) = 2*). Also suggest the importance of particle settling velocity control in sedimentation. (6 marks) (b) The detention time of a sedimentation tank is 2 hours. The horizontal flow is 0.87 m3/s, flow velocity is 0.02 m/s. The width to length ratio of the tank is 1 to 5. If the settling time of particle is just equal to detention time of the tank, find the minimum particle radius. Assume the water temperature is 20°C and the particle density is 1800 kg/m². (9 marks) (c) In a certain day, a worker recorded that 75% of particle in sewage is removed. Assume the water temperature and particle sity remained the same. Find the average particle diameter on that day. He claims that if the sewage is treated again with the same sedimentation tank, the overall particle removal rate will be 93.75%. Do you agree with him? Please explain. (6 marks) (d) Comment on the design at (b). (Hints: Consider the relationship between the dimensions of tank and the performance of sedimentation) (4 marks)