DESIGN OF WATER TREATMENT PLANT FOR A HILLY TERRAIN

Abstract

The primary objective of water treatment plant is to provide water that is safe for human consumption, is appealing to the consumer, non corrosive and non scaling. Moreover, the quantity of treated water should be sufficient to meet the maximum water demand of the population to be served at the design year. The design of water treatment plant mainly involves the selection of appropriate treatment processes/train and design of various treatment units selected. The treatment process can be as simple as involving only one unit operation or unit process, or it can be a combination of few or many unit operations and processes. The selection of a particular water treatment train mainly depends on raw water characteristics, desired level of treated water and the availability of funds, whereas, the capacity of treatment plant depends on design period, population and water demand. The selection and design of treatment processes also depends on state design criteria, topography and site conditions, hydraulic requirements, land area available, sludge disposal, and energy requirements. In the present study, the water treatment plant for Almora town of Uttarakhand has been discussed. Almora is an important and fast growing hill town situated in the Kumaon region of Uttarakhand State of India having a population of 43960 in 2001 census. The town has been facing a shortage in water supply since last few years mainly due to increase in population, and if the present growth rate continues, there will be severe water crisis in the area in the near future. Hence, augmentation of the existing water supply scheme is projected by the authority by tapping Kosi River. The proposed intake point located at about 13 km from Matela, where centralized water treatment plant is proposed to be located. Single well type of a river intake or Jack well is most suited by the site condition, hence, selected. Low lift pump house is proposed to be located on top of jack well intake, and raw water shall be pumped first to pre-sedimentation tank located at suitable place downstream of the intake. The clearer water from plain sedimentation tank is collected into raw water storage/sump which is then lifted to main water treatment plant at Matela through a static head of about 58 m. The analysis of Kosi raw water indicates that most of the parameters are within the allowable limits of Indian drinking water standards except that for turbidity, iii iron, total coliform organisms and slight excess in chromium, dissolved oxygen and biochemical oxygen demand. The turbidity level of Kosi water is high and is as much as 1500 NTU during high flow season. Hence, conventional water treatment plant which consists of mechanical rapid mixer, clariflocculator and rapid singular media filter, preceded by pre-sedimentation and aeration is selected to remove or reduce the undesirable characteristics of raw water. Pre-sedimentation tank is longitudinal flow plain sedimentation tank. For aeration, gravity cascade aerator is selected. Chlorine is proposed for disinfection of filtered water and to ensure residual chlorine of about 0.2 mg/l in the distribution lines. The design of various treatment units are carried out as per design parameters and guidelines given in I.S. Codes, GOI Manual on water treatment plant (1999). The various issues and challenges in the design of water treatment plant have been discussed in detail.