(a) Discuss the following aspects related to sedimentation: (i) Explain the difference between surface overflow rate and hydraulic residence time and the role of each in settling behaviour. (6) (ii) Give a brief discussion of the factors that affect sedimentation efficiency and explain the effect of each factor (8) (b) Discuss/describe the following aspects with reference to design and operation of sand filters (i) (ii) Single media vs. multimedia filtration: advantages, problems, applications. (10) Formation of mud balls, preventing mud ball formation, cleaning of filter media. (8) (iii) The importance of effective back-washing to ensure sustainable production of filtered water of the required quality. (6)