[Saminu, 2(7): July, 2013] ISSN: 2277-9655 Impact Factor: 1.852 http: // www.ijesrt.com (C) International Journal of Engineering Sciences & Research Technology [1694-1699] IJESRT INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY Design and Construction of a Model Sedimentaion Tank Using Existing Slow Sand Filter For NDA Treatment Plant A Saminu *1 , UTsoho 2 , G Harunaand 3 , L Sagir 4 *1,2,3 Department of Civil Engineering, Nigerian Defence Academy, Kaduna 4 Department of Electrical Engineering, Nigerian Defence Academy, Kaduna Abstract The treatment of water for human consumption involves various processes in which raw water passes through. This processes includes; screening, flocculation/coagulation, sedimentation, filtration and chlorination. Sedimentation is a process between flocculation/coagulation tank and filtration tank. The design of sedimentation tank is necessary to receive effluent of the flocculation/coagulation tank and achieve efficient settling of particles under gravity and then discharge to the slow sand filter as effluent for further treatment. To achieve this grate settling efficiency, a rectangular sedimentation tank withthe following dimensions; depth 3.58m, width 5.76m and 23.0m long, is designed and constructed with a baffle across the inlet perforated with holes, this provides calm area at the settling zone for efficient settling of particles. The base of the tank is sloped towards the inlet zone for collection and disposal of sludge gate valve. While at the outlet zone, a baffle is provided to prevent any particle which did not settle from going out. Introduction Water to be supplied for public use must be portable i.e. satisfactory for drinking purposes from the stand point of its chemical, physical and biological characteristics. Drinking water should preferably be obtained from source free from pollution. The raw water normally available from surface water source is how ever not directly suitable for drinking purpose. The objective of water treatment plant is to continuously provide a portable supply of water. It should also improve the athletic acceptability of the water and remove any toxic or health-hazardous material. Other function is to remove or deactivate a diseases-producing organism. All surface water and ground water require treatment prior to consumption to ensure they do not represent a health risk to the user. Health risk to consumers from poor quality can be due to microbiological, chemical, physical or radioactive contamination. Some of the common treatment process used in the past includes plain sedimentation, slow and filtration, rapid sand filtration with coagulation-flocculation units as essential pretreatment units. Pressure filters and diatomaceous filters have been used, under certain circumstances, as pretreatment units for the conventional filters. Definition of Sedimentation Sedimentation or classification is the processes of letting suspended material settle by gravity. Suspended material may be particles such as clay or silts originally present in the source water. More commonly, suspended materials or floc is created from material in the water and the chemical used in coagulation or in the treatment processes, such as lime softening. Sedimentation is the removal of suspended solids through the setting of particles moving through a tank at a slow rate. There are a number of forms of sedimentation. In water treatment plants, treating source water a high proportion of suspended solids of coarse grade level e.g. clay and coarse silt) a grit chamber may be used to remove the largest particles through simple sedimentation. In this process, water is passed through a tank at a slow rate and suspended solids fall out of suspension. In small supplies simple sedimentation may also be used, while functioning in a simple fashion to grit chambers, although with a smaller rate of water through flow. Simple sedimentation will not remove fine-grained particles because the flow remains too high and the retention time is insufficient. A further common fault with simple sedimenters is that design flow rates are rarely achieved in practice and a certain element ‘short- circuiting’ can occur unless construction, operation and maintenance is done in a careful manner. As a result of the drawbacks in simple sedimentation, it is common to find that the sedimentation process is enhanced through the addition of chemicals.