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# water supply and Treatment (2).pptx

water supply and treatment short summary

water supply and treatment short summary

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### water supply and Treatment (2).pptx

1. 1. Water Supply & Treatment Tutorial class for HWRE GC students January 2023
2. 2. Course Objectives ◦ Learning objectives can be formulated as: 🞄 The objective of this course is to give students a broad understanding of population forecasting, water demand, water source, collection, and distribution of water. 🞄The general idea about water supply and water treatment techniques
3. 3. 1.QUANTITY OF WATER  Introduction  In the design of any water work projects, it is necessary to estimate the amount of water that is required. This involves: served – Determination of people who will be – per capita water consumption – Analysis of the factors
4. 4. 1.2 Types of demands  Various Types of Demands  Domestic water demand  Industrial and commercial water demand  Demand for public use  Fire demand  Water required to compensate losses in wastes
5. 5. Water Demand Domestic water demand • This includes the water required in private buildings for drinking, cooking, bathing, gardening, sanitary purposes, etc. • The total domestic consumption generally amounts to 55 to 60% of the total water consumption. Industrial & commercial water demand • This includes the quantity of water required to be supplied to offices, factories, different industries, big hotels, hospitals, etc. 20 to 25% of the total water consumption.
6. 6. Water Demand  Demand for public use • This includes the quantity of water required for public utility purposes, such as watering of public parks, gardening, washing and sprinkling on the roads, use in public fountains and etc.  Fire demand • The quantity of water required to fight fire. There are formulas to estimate Fire demand ,
7. 7. a. National board of fire underwriter formulas. Q = 64 √ P (1 – 0.01√P) Where Q = rate of flow of water in l/sec P = Population in thousand b. Freeman formula. Q = 1135.5 ((P⁄ 10) + 10) Where Q is in lit/min c.Kuichling formula. Q = 3182 √P Where Q is in lit / min P is in thousands Fire demand cont.…
8. 8. Water Demand  Water required to compensate losses in wastes – this includes the water lost in leakage due to bad plumbing or damage meters, stolen water due to unauthorized water connections and other losses. – Generally ,allowance of 15 – 20% of total quantity of water is made to compensate for the losses.
9. 9. Factors Affecting Water Demand o Size of the city o Climatic condition o Characteristics of population o Quality of water supplies o Pressure in distribution system o Cost of water o System of supply o Policy of metering and method of charging
10. 10. Factors Affecting water demand  Size of City The per capita water demand of the town, will increase with the size of the town, because more water will be required in street washing, running of sewers, maintenance of parks and gardens  Climatic condition The quantity of water required in hotter and dry places is more due to use sprinkling of water in garden, washing of clothes and bathing.
11. 11. Factors Affecting Water Demand  Living standard of the people The per capita demand of the town increase with the standard of living of the people. The people will start using room coolers, use of flush latrines, use of automatic dish washing and others.  pressure in the distribution system the rate of water consumption increases with the increase in the pressure of the distribution system. The water reaches the upper storey of the building only if it is released with the required pressure. If the pressure ⭡- more water loss due to leakage, wastage
12. 12. Variation in rate of consumption  Per capita demand: means the annual consumption of water. It was therefore, defined as the annual average daily consumption per person. per capita Demand = Q / P*365 Where Q: – is the total quantity of water required by a town per year in liter. P: - The population of the town  seasonal variation: Large amount of water uses in summer season, and lesser user in winter.
13. 13. Design Period and Population Forecasting  Design period  The number of years for which the designs of water works have been done is known as design period. These period should neither be too short or too long.  Mostly water works are designed for design period of 20 – 30 years.
14. 14. Factor, which should be kept in view while fixing the design period:  Fund  The life of the material used in project (pipes, structural materials )  Anticipated expansion of the town  The rate of interest on the loan taken
15. 15. Population Forecasting  When the design period is fixed the next step is to determine the population in various periods, because the population of the towns generally goes on increasing.  There are three major factors which affect change in population: – Birth – Death – Migration
16. 16. Population forecasting  Methods of population forecasting  Arithmetical increase method  Geometrical increase method  Incremental increase method  Decreasing rate method  Logistic Curve method  Simple graphical method  Master plan method  CSA method
17. 17. Arithmetical increase method Pn = Po + nK Where; Pn = population at n decades or years Po = present/initial population at the base year n = decade or year K= arithmetic increase This method is generally applicable to large and old cities.
18. 18. o Geometrical increase method ⚫ In this method it is assumed that the percentage increase in population from decade to decade remains constant. ⚫ If the present population is Po and average percentage growth is k, the population at the end of n decade will be: Pn = po (1 + k)n where po = initial population ,Pn = popn at n decades ,n = Decades & k = Percentage (geometric) increase  This method is mostly applicable for growing towns and cities having vast scope of expansion.
19. 19.  Incremental increase method This method is the combination of the above two methods and, therefore gives the advantages of both arithmetic and geometric increase methods and gives satisfactory results. Decreasing rate method  In this method, the average decrease in the percentage increase is worked out and is then subtracted from the late percentage increase for each successive decades.  This method is applicable to average size cities growing under normal condition
20. 20. Logistic Curve method When the population of a town is plotted with respect time the curve so obtained under normal condition is s – shaped curve and is known as logistic curve.
21. 21. CSA method Pn  Po * e kn Where, Pn = population at n decades or years Po = initial population n = decade or year k = growth rate in percentage Is a Method used by the Ethiopian statistic Authority for population forecasting
22. 22. Water Sources  Sources of Water Supply – The origin of all water is rainfall – Water can be collected  as it falls  as rain before it reaches the ground  as surface water when it flows over the ground  as ground water when it percolates in to the ground
23. 23. Water Sources  All the sources of water can be broadly divided into: – Surfaces sources and – Sub surface sources  Surfaces Sources The surface sources further divided into – Streams and rivers – Ponds and Lakes – Impounding reservoirs etc.
24. 24.  Subsurface Sources These are further divided into – Infiltration galleries – Infiltration wells – Springs  Gravity Springs  Surface Spring  Artesian Spring – Wells
25. 25. Water Sources  Wells – A well is defined as an artificial hole or pit made in the ground for the purpose of tapping water – types of wells  Shallow wells  Deep wells  Tube wells  Artesian wells
26. 26. Intakes for Collecting Surface Water  The main function of the intakes works is to collect water from the surface source  Intakes are structures which essentially consist of opening, grating or strainer through which the raw water from river, canal or reservoir enters
27. 27. Intakes for Collecting Surface Water  Types of Intake structures – Depending upon the source of water the intake works are classified as following  Lake Intake  Reservoir Intake  River Intake  Canal Intake –
28. 28. Lake Intake  These intakes are constructed in the bed of the lake below the water level; so as to draw water in dry season also
29. 29. River Intake  Water from the rivers is always drawn from the upstream side, because it is free from the contamination caused by the disposal of sewage in it
30. 30. Reservoir Intake  It consists of an intake well, which is placed near the dam and connected to the top of dam by Foot Bridge
31. 31. Canal Intake  An intake chamber is constructed in the canal section
32. 32. Water Sources Selection Criteria  Location: The sources of water should be as near as to the town as possible.  Quantity of water: the source of water should have sufficient quantity of water to meet up all the water demand through out the design period.  Quality of water: The quality of water should be good which can be easily and cheaply treated.  Cost: The cost of the units of the water supply schemes should be minimum.
33. 33. Water quality and pollution  Absolutely pure water is never found in nature and contains number of impurities in varying amounts  The rainwater which is originally pure also absorbs various gases, dust and other impurities while falling  The water supplied to the public should be strictly according to the standards laid down from time to time
34. 34. Water Quality Characteristics  impurities present in water may be divided into the following three categories – Physical Characteristics – Chemical Characteristics – Biological Characteristics
35. 35. Water Quality Characteristics  Physical characteristics – Turbidity – Color – Taste and odor – Temperature
36. 36. Water Quality Characteristics  Chemical characteristics – Total solids – Alkalinity – pH – Dissolved oxygen – BOD, COD – Nitrogen – Hardness (calcium & Magnesium)
37. 37.  biological characteristics – Bacterium – Viruses – Algae – protozoa Water Quality Characteristics
38. 38. Water quality standards Parameter WHO guideline Recommended for Ethiopia pH 6.5-8.5 5.0-9.5 Total solids, mg/L 1000 2000 Total hardness, mg/L 500 600 Chloride, mg/L 250 800 Sulphate, mg/L 400 600 Fluoride, mg/L 1.5 4 Iron, mg/L 0.3 3 E. Coli, MPN/100 ml 10 30 Nitrate , mg/L 10 40
39. 39. Sources of Water Pollution  Following are the main sources of water pollution. – Domestic sewage – Industrial wastes – Agricultural areas – Distribution system
40. 40. WATER TREATMENT  The process of removing the impurities from water is called water treatment and the treated water is called wholesome water  The surface sources generally contains large amount of impurities therefore they requires sedimentation, filtration and chlorination as treatment  Groundwater which is usually clear may require only disinfection
41. 41. Water Treatment  Methods of Water Treatment – Aeration – Screening and grit removal – Plain sedimentation – Coagulation and flocculation – Secondary sedimentation – Filtration – Adsorption – Softening – Disinfections
42. 42. Aeration  It is the process of bringing water in intimate contact with air, while doing so water absorbs oxygen from the air  Aeration may be used to remove undesirable gases dissolved in water i.e. Co2, H2S,  Different types of aerators are available – Gravity Aerator – Spray aerator – Air diffuser – Mechanical Aerator
43. 43. Aerators  Gravity aerators A. Cascade towers Inlet chamber Collection Chamber
44. 44. Aerators B. Inclined apron possibly shaded with plates Inlet chamber Collection Chamber
45. 45. Aerators C. Tray aerator – In tray aerator water falls through a series of trays perforated with small holes, 5 - 12mm diameter and 25 - 75mm spacing center to center
46. 46. Aerators  Spray aerators – spray droplets of water into the air from stationary or moving orifices or nozzles – Water is pumped through pressure nozzles to spray in the open air as in fountain to a height of about 2.5m
47. 47. Aerators  Air diffuser – Compressed air is forced into this system through the diffusers – This air bubbles up through the water, mixing water and air and introducing oxygen into the water
48. 48. Aerators  Mechanical Aerator – These aerators work by vigorously agitating the water with mechanical mixers
49. 49. Screening  Screening usually involves a simple screening or straining operation to remove large solids and floating matter as leaves, dead animals, fish etc. – Bar screens - with openings of about 75mm – Mesh screens - with opening of 5 - 20mm
50. 50. Plain Sedimentation  Sedimentation is the removal of particles (silt, sand, clay, etc.) through gravity settling in basins  No chemicals is added to enhance the sedimentation process  Principle of plain sedimentation - Discrete particles
51. 51. sedimentation vc: critical velocity, m/h Q: flow rate, m3/h Td: detention time, h A: area of top of basin settling zone, m2 SOR: surface overflow rate, m3/m2.h
52. 52. Sedimentation Tank  The velocity of flow can be reduced by increasing the length of travel and by detaining the particle for a longer time in the sedimentation basin  The size and the shape of the particles can be altered by the addition of certain chemicals in water (coagulants)  Sedimentation Tanks are generally made of reinforced concrete and may be rectangular or circular in plan  Long narrow rectangular tanks with horizontal flow are generally preferred to the circular tanks with radial or spiral flow
53. 53. Sedimentation Tank
54. 54. Sedimentation Tank
55. 55. Inlet zone  to distribute the water inside the tank  to control the water's velocity as it enters the basin  A most suitable type of an inlet for a rectangular settling tank is in the form of a channel extending to full width of the tank with a submerged weir type baffle wall
56. 56. Inlet zone  E
57. 57. Out let zone  Outlet arrangement consists of – weir, notches or orifices – effluent trough or launder – outlet pipe
58. 58. Design parameters of sedimentation tank 1. Detention period ….. 3 to 4 hours for plain settling 2 to 2.5 hours for coagulant settling 1 to 1.5 hours for vertical flow type 2. Overflow rate ……… 15 - 30 m3/m2/day for plain settling 30 - 40m3/m2/day for horizontal flow 40 - 50m3/m2/day for vertical flow 3. Velocity of flow…….. 0.5 to 1.0 cm/sec 4.Weir loading………... 300m3/m/day 5. L:W ………………….. 3:1 to 5:1 Breadth of tank…….. (10 to 12m) to 30 to 50m 6. Depth of tank………. 2.5 to 5m (with a preferred value of 3m) 7. Diameter of circular tank…. up to 60m 8. Solids removal efficiency….. 50% 9. Turbidity of water after sedimentation – 15 to 20 NTU. 10. Inlet and Outlet zones………. 0.75 to 1.0m 11. Free board…………………… 0.5m 12. Sludge Zone…………………. 0.5m
59. 59. What is Coagulation?  Coagulation is the destabilization of colloids by addition of chemicals that neutralize the negative charges  The chemicals are known as coagulants, usually higher valence cationic salts (Al3+, Fe3+ etc.)  Coagulation is essentially a chemical process
60. 60. Coagulation (Coagulation Aided with Sedimentation)  To remove very fine particles from the water  Adding of this chemical process is called coagulation and the chemical used in the process is called coagulant  Objective, to form a flocs
61. 61. Typical coagulants  Aluminum sulfate: Al2(SO4)3.14 H2O  Iron salt- Ferric sulfate: Fe2(SO4)  Iron salt- Ferric chloride: Fe2Cl3  Polyaluminum chloride (PAC): Al2(OH)3Cl3
62. 62. Coagulation aim 96
63. 63. Colloidal interaction 97
64. 64. Charge reduction 98
65. 65. Colloid Destabilization be destabilized by charge  Colloids can neutralization  Positively charges ions (Na+, Mg2+, Al3+, Fe3+ etc.) neutralize the colloidal negative charges and thus destabilize them.  With destabilization, colloids aggregate in size and start to settle 99
66. 66. Jar Tests  The jar test – a laboratory procedure to determine the optimum pH and the optimum coagulant dose  A jar test simulates the coagulation and flocculation processes
67. 67. Jar Tests  Determination of optimum pH  Fill the jars with raw water sample (500 or 1000 mL) – usually 6 jars  Adjust pH of the jars while mixing using H2SO4 or NaOH/lime (pH: 5.0; 5.5; 6.0; 6.5; 7.0; 7.5) Add same dose of the selected coagulant (alum or iron) to each jar (Coagulant dose: 5 or 10 mg/L) Jar Test
68. 68. Determination of optimum pH  Rapid mix each jar at 100 to 150 rpm for 1 minute. The rapid mix helps to disperse the coagulant throughout each container Reduce the stirring speed to 25 to 30 rpm and continue mixing for 15 to 20 mins. This slower mixing speed helps promote floc formation by enhancing particle collisions, which lead to larger flocs  Turn off the mixers and allow flocs to settle for 30 to 45 mins  Measure the final residual turbidity in each jar  Plot residual turbidity against pH
69. 69. Jar Tests – optimum pH Optimum pH: 6.3
70. 70. Optimum coagulant dose  Repeat all the previous steps  This time adjust pH of all jars at optimum (6.3 found from first test) while mixing using H2SO4 or NaOH/lime Add different doses of the selected coagulant (alum or iron) to each jar (Coagulant dose: 5; 7; 10; 12; 15; 20 mg/L)  Rapid mix each jar at 100 to 150 rpm for 1 minute. The rapid mix helps to disperse the coagulant throughout each container  Reduce the stirring speed to 25 to 30 rpm for 15 to 20 mins
71. 71. Optimum coagulant dose  Turn off the mixers and allow flocs to settle for 30 to 45 mins  Then measure the final residual turbidity in each jar  Plot residual turbidity against coagulant dose The coagulant dose with the lowest residual turbidity will be the optimum coagulant dose Coagulant Dose mg/L Optimum coagulant dose: 12.5 mg/L
72. 72. Filtration  Removal of colloidal (usually destabilized) and suspended material from water by passage through layers of porous media.
73. 73. Types of Granular Filters  Based on filter media – Slow sand filtration – Rapid filtration – High-rate filters  Based on driving force – Gravity filters – Pressure filters  Based on flow direction – Down flow filters – Up flow filters
74. 74. Particle Removal Mechanisms in Filters
75. 75. Filter media size parameters – Effective size (d10): the size of standard sieve opening that will pass 10% by weight of the media – Uniformity coefficient (UC): the ratio of the standard sieve opening that will pass 60% by weight of the media (d60) to its effective size. 10 60 d  d UC
76. 76.  Slow sand filter consists of concrete/brick work rectangular basin containing carefully selected graded sand supported on gravel and stones. Slow Sand Filter
77. 77. Mechanisms of impurities removal in SSF  Physical:Mechanical straining/sedimentation  Chemical: Oxidation of organic matter by aerobic bacteria  Biological: Occurs through Schmutzdecke or “Vital layer”. Schmutzdecke is a layer of dirt, debris, and microorganisms build up on the top of the sand
78. 78. Slow Sand Filter Cleaning  Periodic raking and cleaning of the filter by removing the top two inches of sand. After a few cleanings, new sand must be added to replace the removed sand.  After a cleaning the filter must be operated for two weeks, with the filtered water sent to waste, to allow the schmutzdecke layer to rebuild.  Two slow sand filters should be provided for continuous operation.
79. 79. Advantages and Disadvantages of SSF  Advantages: – Simple to construct and operate – Cost of construction cheaper than rapid sand filter – Do not usually require coagulation/flocculation before filtration – Bacterial count reduction is 99.9% to 99.99% and E.coli reduction is 99% to 99.9%  Disadvantages: – Initial cost is low but maintenance cost is much more than rapid sand filter – These filters need a lot of space
80. 80. Design criteria for slow sand filters Parameter Recommended level Design life 10-15 year Period of operation 24 h/day Filtration rate 0.1 – 0.2 m/h Filter bed area 5-200 m2/filter Height of filter bed Initial 0.8-0.9 m Minimum 0.5-0.6 m Effective size 0.15-0.3 mm Uniformity coefficient < 3 Height of under drains including 0.3-0.5 m gravel layer Height of supernatant water 1 m
81. 81. Disinfection  Treatment used for destruction or removal of pathogens  Widely used disinfectants – Oxidizing agents (halogens, halogen compounds, ozone) – Physical agents (Ultraviolet radiation)  Factors that affect efficiency of disinfection – Type and concentration of microorganisms – Type and concentration of disinfectant – Contact time provided – Character and temperature of the water
82. 82. Characteristics of an Ideal Disinfectant  Kill or disable pathogens  Nontoxic to consumers  Cheap and easy to use  Fast acting and long lasting  Improve water aesthetics
83. 83. Disinfectants in common use  Chlorine (Cl2)  Chloramines (NH2Cl, NHCl2)  Chlorine dioxide (ClO2)  Ozone (O3)  Ultraviolet (UV) radiation.
84. 84. Chlorination  Widely used disinfectant  Advantages: readily available as gas, liquid or solid; cheap; easy to apply; toxic to most microorganisms; provides protection in the distribution system  Disadvantages: Fatal at high concentrations; Toxic; Irritant; Corrosive; Formation of harmful disinfection by-products (DBPs) like Trihalomethanes (THMs)
85. 85. Chloramines  Advantages – Less corrosive – Less toxicity and chemical hazards – Relatively tolerable to inorganic and organic loads – No known formation of DBP – Relatively long-lasting residuals  Disadvantages – Not so effective against viruses, protozoan cysts, and bacterial spores
86. 86. Chlorine gas cylinder
87. 87. Hypochlorites  Less pure and dangerous than chlorine gas  Strength decreases with time while in storage  Safer to handle but expensive  Types: – Sodium hypochlorite (NaOCl) solution – Calcium hypochlorite (CaO(Cl)2)  Reactions: Ca(OCl)2 + 2 H2O  2 HOCl + Ca(OH)2 NaOCl + H2O  HOCl + NaOH
88. 88. UV Disinfection  Physical method of inactivating pathogens.  Mechanism of UV Disinfection: – Radiation with an wavelength of around 260 nm penetrates the cell wall and cell membrane of microorganisms and is absorbed by cell material such as DNA and RNA and promotes changes that prevents replication to occur
89. 89. Miscellaneous Water Treatment Processes  Removal of dissolved gases  Removal of Iron and manganese  Removal of silica  Fluoridation  Removal of oil  Softening (refer the removal of hardness in chapter three)
90. 90. WATER DISTRIBUTION SYSTEM  After treatment, water is to be stored temporarily and supplied to the consumers through the network of pipelines called distribution system.  The distribution system also includes – pumps, – reservoirs, – pipe fittings, – instruments for measurement of pressures, flow leak detectors etc
91. 91. Requirement of Distribution System  The system should convey the treated water up to consumers with the same degree of purity  The system should be economical and easy to maintain and operate  It should safe against any future pollution. As per as possible should not be laid below sewer lines.  Water should be supplied without interruption even when repairs are undertaken  The system should be so designed that the supply should meet maximum hourly demand
92. 92. System of Distribution  Depending upon the methods of distribution, the distribution system is classified as the follows – Gravity system – Pumping system – Dual system or combined gravity and pumping system
93. 93. Gravity System  When some ground sufficiently high above the city area is available
94. 94. Pumping System  Constant pressure can be maintained in the system by direct pumping into mains  Supply can be affected during power failure and breakdown of pumps
95. 95. Combined Pumping and Gravity System
96. 96. Methods of Supply of Water  Continuous System – This is the best system and water is supplied for all 24 hours. This system is possible when there is adequate quantity of water for supply.  Intermittent System – If plenty of water is not available, the supply of water is divided into zones and each zone is supplied with water for fixed hours in a day or on alternate days
97. 97.  The system has following disadvantages: – Consumers have to store water for non-supply hours. – Bigger sized pipes are to be laid, because full day’s supply is to be provided within few hours of supply. – Pipelines are likely to rust faster due to alternate wetting and drying. This increases the maintenance cost. – There is also pollution of water by ingress of polluted water through leaks during non-flow periods.
98. 98. Layouts of Distribution System  Generally in practice there are four different systems of distribution which are used. They are: – Dead End or Tree system – Grid Iron system – Circular or Ring system – Radial system
99. 99. Dead End or Tree System  This system is suitable for irregular developed towns or cities.
100. 100. Dead End or Tree System  Advantages: – Discharge and pressure at any point in the distribution system is calculated easily – The valves required in this system of layout are comparatively less in number. – The diameter of pipes used are smaller and hence the system is cheap and economical – The laying of water pipes is used are simple.
101. 101. Dead End or Tree System  Disadvantages: – There is stagnant water at dead ends of pipes causing contamination. – During repairs of pipes or valves at any point the entire downstream end are deprived of supply – The water available for firefighting will be limited in quantity
102. 102. Grid Iron System  From the mains water enters the branches at all junctions in either direction into sub-mains of equal diameters.
103. 103. Grid Iron System  Advantages – As water is supplied from both the sides at any point, very small distribution area will be affected during repair. – Every point receives supply from two directions and with higher pressure – In case of fire, more quantity of water can be diverted towards the affected area, by closing the valves of nearby localities. – There is free circulation of water and hence it is not liable for pollution due to stagnation.
104. 104. Grid Iron System  Disadvantages: – More length of pipes and number of valves are needed and hence there is increased cost of construction – Calculation of sizes of pipes and working out pressures at various points in the distribution system is laborious, complicated and difficult.
105. 105. Circular or Ring System  Supply to the inner pipes is from the mains around the boundary. It has the same advantages as the grid-Iron system. Smaller diameter pipes are needed. The advantages and disadvantages are same as that of grid-Iron system.
106. 106. Circular or Ring System
107. 107. Radial System  Water is pumped to the distribution reservoirs and from the reservoirs it flows by gravity to the tree system of pipes.  The pressure calculations are easy in this system. Layout of roads needs to be radial to eliminate loss of head in bends. This is most economical system also if combined pumping and gravity flow is adopted.
108. 108. Radial System
109. 109. Pressure in the Distribution System  When the water enters in the distribution main, the water head continuously is lost due to friction in pipes, at the entrance of reducers, due to valves, bends, meters etc till it reaches the consumers tap  The effective head available at the service connection to a building is very important, because the height up to which the water can rise in the building will depend on this available head only
110. 110. The pressure in the distribution system depends upon the factors as listed below: – The height of highest building where water should reach with adequate pressure, without boosting – Pressure required for fire hydrant – The distance of the locality from the distribution reservoir.
111. 111. The following pressures are considered satisfactory in the case of multi-storied buildings.  One storey only 7m head  Two storey building 12m head  Three storey building 17m head  3 to 6 storey heights 2.1 to 4.2kg/cm2 (21 to 42m)  6 to 10 storey heights 4.2 to 5.2kg/cm2  Above 10 storey 5.27 to 7kg/cm2
112. 112. Service/Distribution Reservoirs  A service reservoir has four main functions: – To balance the fluctuating demand from the distribution system, permitting the source to give steady or differently phased output. – Provide a supply during a failure or shutdown of treatment plant, pumps or trunk main leading to the reservoir. – To give a suitable pressure for the distribution system and reduce pressure fluctuations therein. – To provide a reserve of water to meet fire and other emergency demands.
113. 113. Types of Service Reservoirs  Generally, there are two types of service reservoirs: – Surface reservoir (Ground Reservoir or Non-elevated) – Elevated reservoir ( Over head Tank)
114. 114. Accessories of Service Reservoirs  Inlet Pipe : For the entry of water  Ladder : To reach the top of the reservoir and then to the bottom of the reservoir, for inspection and cleaning  Lightening Conductor : In case of elevated reservoirs for the passage of lightening  Manholes : For providing entry to the inside of reservoir for inspection and cleaning  Outlet pipe: For the exit of water
115. 115. Cont’d  Outflow Pipe : For the exit of water above full supply level  Vent pipes : For free circulation of air  Washout pipe : For removing water after cleaning of the reservoir  Water level indicator: To know the level of water inside the tank from outside.
116. 116. Accessories of service reservoir LIGHTENING CONDUCTOR OUTLET PIPE INFLOW PIPE WATER LEVEL INDICATOR WASH OUT PIPE DITCH OVER FLOW PIPE MANHOLE LADDER
117. 117. Design Capacity of Service Reservoirs  Analytically by finding out maximum cumulative surplus during the stage when pumping rate is higher than water consumption rate and adding to this maximum cumulative deficit which occurs during the period when the pumping rate is lower than the demand rate of water
118. 118.  By drawing mass curves (graphical method) – A mass diagram is the plot of accumulated inflow (i.e. supply) or outflow (i.e. demand) versus time. The mass curve of supply (i.e. supply line) is, therefore, first drawn and is superimposed by the demand curve.
119. 119. Example 1:  A small town with a design population of 1600 is to be supplied water at 150liters per capita per day. The demand of water during different periods is given in the following table: Time (hr) 0 - 3 3 - 6 6 - 9 9 - 12 12 - 15 15 - 18 18 - 21 21- 24 Demand (1000lit ers) 20 25 30 50 35 30 25 25 • Determine the capacity of a balancing reservoir if pumping is done 24 hours at constant rate.
120. 120. Solution:  Per capita water consumption = 150l/c/d  Total water demand = demand * population = 150*1600 = 240,000liters  Rate of pumping = 240,000/24 = 10,000lit/hr = 30,000lit/3hr
121. 121. Analytical Method Time Pumping Demand Cum. Supply Cum. Demand Surplus Deficit 0 - 3 30,000 20,000 30,000 20,000 10,000 3 - 6 30,000 25,000 60,000 45,000 15,000 6 - 9 30,000 30,000 90,000 75,000 15,000 9 - 12 30,000 50,000 120,000 125,000 5,000 12 - 15 30,000 35,000 150,000 160,000 10,000 15 - 18 30,000 30,000 180,000 190,000 10,000 18 - 21 30,000 25,000 210,000 215,000 5,000 21 - 24 30,000 25,000 240,000 240,000 0 0
122. 122. Cont’d  Maximum cumulative surplus = 15,000 liters  Maximum cumulative deficit = 10,000 liters  Balancing storage = 15000 + 10000 = 25,000lit = 25m3 If the reservoir is circular with depth, h = 3.0 m, m d 4 . 3 3 4 * 25   
123. 123. Mass curve method
124. 124. Example 2 Consider example 1, if the pumping is done for: – Eight hours from 8 hrs to 16 hrs – Eight hrs from 4 hrs to 8 hrs and again 16 hours to 20 hrs. Calculate the capacity of the balancing reserve. Solution:  Total water demand = 240,000lit/hr  Rate of pumping = 240,000/8 = 30,000l/h = 90,000lit/3hrs
125. 125. Eight hours from 8 hrs to 16 hrs A) Analytical Method Time Pumping Demand Cum. Supply Cum. Demand Surplus Deficit 0 - 3 0 20000 0 20000 20000 3 - 6 0 25000 0 45000 45000 6 - 8 0 20000 0 65000 65000 8 - 9 30000 10000 30000 75000 45000 9 - 12 90000 50000 120000 125000 5000 12 - 15 90000 35000 210000 160000 50000 15 - 16 30000 10000 240000 170000 70000 16 - 18 0 20000 240000 190000 50000 18 - 21 0 25000 240000 215000 25000 21 - 24 0 25000 240000 240000 0 0
126. 126. Maximum cumulative surplus = 70,000 Maximum cumulative deficit = 65,000 Balancing storage, S = 135,000lit = 135m3
127. 127. B) Graphical Method
128. 128. Depth and Shape of Service Reservoirs  Depth Size (m3) Depth of water (m) Up to 3500 2.5 to 3.5 3500 to 15,000 3.5 to 5.0 Over 15,000 5.0 to 7.0
129. 129. Factors influencing depth for a given storage are:  Depth at which suitable foundation conditions are encountered  Depth at which the out let main must be laid  Slope of ground, nature and type of back fill  The need to make the quantity of excavated material approximately equal to the amount required for backing, so as to reduce unnecessary carting of surplus material to tip.  The shape and size of land available
130. 130. Shape  Circular reservoir is geometrically the most economical shape, giving the least amount of walling for a given volume and depth  A rectangular reservoir with a length to width ratio 1.2 to 1.5
131. 131. Pipes Used in the Water Distribution System Pipe Materials  Pipe materials used in transmission and distribution systems must have the following characteristics – Adequate tensile strength and bending strength to withstand external loads. – High bursting strength to withstand internal water pressure – Ability to resist impact loads to water flow suitable for handling and joining facilities – Resistance to both internal and external corrosion
132. 132. The types of pipes used for distributing water include:  Cast iron pipe  Steel pipe  Concrete pipe  Plastic pipe  Asbestos cement pipe  Copper pipe  Lead pipe
133. 133. A pipe material is selected based on various conditions:  Cost  Type of water to be conveyed  Carrying capacity of the pipe  Maintenance cost  Durability, etc.
134. 134. Cast iron pipes  Advantages: – The cost is moderate – The pipes are easily joined – The pipes aren’t subjected to corrosion – The pipes are strong and durable – Service connections can be made easily – Disadvantage: – The breakage of this pipe is large – Carrying capacity decreases with increase in life – The pipes become heavy and uneconomical when their sizes increase (especially beyond 1200mm) Advantages:
135. 135. Galvanized Iron Pipes  Advantages: – The pipes are cheap – Light in weight and easy to handle and transport – Easy to join  Disadvantage: – These pipes are liable to incrustation (due to deposition of some materials inside part of pipe) – Can be easily affected by acidic or alkaline water – Short useful life
136. 136. Plastic Pipes  Advantages: – The pipes are cheap – The pipes are flexible and possess low hydraulic resistance (less friction) – They are free from corrosion – The pipes are light in weight and it is easy to bend, join and install them – The pipes up to certain sizes are available in coils and therefore it becomes easy to transport
137. 137.  Disadvantage: – The coefficient of expansion for plastics is high, the pipes are less resistant to heat – Some types of plastics may impart taste to the water
138. 138. Appurtenances in the Distribution System  The various devices fixed along the water distribution system are known as appurtenances.  The following are the some of the fixtures used in the distribution system. – Valves – Fire hydrants and – Water meter
139. 139. Types of Valves  The following are the various types of valves named to suit their function – Sluice valves – Check valves or reflex valves – Air valves – Drain valves or Blow off valves – Scour valve
140. 140. Valves Sluice valves – These are also known as gate-valves or stop valves. – These valves control the flow of water through pipes. Check Valve or Reflux Valve – These valves are also known as non-return valves. A reflux valve is an automatic device which allows water to go in one direction only
141. 141. Sluice valve
142. 142. Air Valves  These are automatic valves and are of two types namely – Air inlet valves – Air relief valves  Air Inlet Valves – These valves open automatically and allow air to enter into the pipeline so that the development of negative pressure can be avoided in the pipelines.
143. 143. – The vacuum pressure created in the down streamside in pipelines due to sudden closure of sluice valves – This situation can be avoided by using the air inlet valves.  Air Relief Valves – Sometimes air is accumulated at the summit of pipelines and blocks the flow of water due to air lock. In such cases the accumulated air has to be removed from the pipe lines.
144. 144.  Drain Valves or Blow off Valves – These are also called wash out valves they are provided at all dead ends and depression of pipelines to drain out the waste water.
145. 145. Water Meter  These are the devices which are installed on the pipes to measure the quantity of water flowing at a particular point along the pipe.  The readings obtained from the meters help in working out the quantity of water supplied and thus the consumers can be charged accordingly.
146. 146. Fire Hydrants  A hydrant is an outlet provided in water pipe for tapping water mainly in case of fire.  They are located at 100 to 150 m a part along the roads and also at junction roads.
147. 147. Determination of Pipe Sizes  Permissible velocities for best results for different pipe sized pipes are within the range of 0.3 to 2m/s.  Once the velocity of flow is established loss of head due to friction, bends and other reasons can be computed  The head required to develop a particular velocity in a particular sized pipe is then calculated.
148. 148.  The size of the pipe used in the water distribution system or the velocity of flow through the pipe can be determined by one of the following formulas:  Darcy –Weisbach formula:  Hazen-Williams formula:  Manning’s Formula: Determination of Pipe Sizes gD fLV hf 2 2  L h S S CD Q f   , 278 . 0 54 . 0 63 . 2 n S AR Q 2 / 1 3 / 2 
149. 149. Determination of Pipe Sizes  The most common pipe flow formula used in design and evaluation of a water distribution system is the Hazen-Williams’ formula. L h S S CD Q f   , 278 . 0 54 . 0 63 . 2
150. 150. Water supply pipes sizes commercially available are given in the following table: Metric sizes (mm) 10 20 25 30 40 50 60 80 100 150 200 250 300 English (In) ½ 3/4 1 11/4 11/4 2 21/2 3 4 6 8 10 12 Metric sizes (mm) 350 375 400 450 500 525 600 675 750 900 950 1050 English (In) 14 15 16 18 20 21 24 27 30 36 38 42
151. 151. Example 1:  Given – Total population of a town = 80,000 – Average daily consumption of water = 150liters/capita/day – If the flow velocity of an outlet pipe from intake = 1.5 m/s, determine the diameter of the outlet pipe.
152. 152. Exp. Cont’d..  Solution  Total flow, Q = Demand* Population = 150*80,000 = 12x106 lit/day  Required pipe area,  But the pipe size available on the market is 300mm & 350mm, then take D = 350mm mm V Q D V Q D V Q A 343 * 5 . 1 4 * 1389 . 0 4 4 4 2         
153. 153. Example 2:  A town has a population of 100,000 persons. It is to be supplied with water from a reservoir situated at a distance of 6.44km. It is stipulated that one-half of the daily supply of 140lit/capita should be delivered in 6 hours. If the loss of head is estimated to be 15m, calculate the size of pipe. Assume f = 0.04.
154. 154. Exp. Cont’d.. Solution  Total daily supply =  Since half of this quantity is required in 6 hours  Maximum flow =  According to the Darcy-Weisbach formula: Where, hf = 15m, f = 0.04, L = 6440m 3 3 000 , 14 10 000 , 100 * 140 m  s m / 324 . 0 ) 60 * 60 * 6 * 2 ( 000 , 14 3  5 2 1 . 12 d fLQ hf 
155. 155.  But available pipe sizes 675mm & 750mm, take 750mm diameter pipe mm m d d 683 683 . 0 10 . 12 * 15 ) 324 . 0 ( * 6440 * 04 . 0 * 1 . 12 ) 0324 ( * 6440 * 04 . 0 15 2 5 2     
156. 156. Energy Losses in Pipes  The major energy loss (head loss) in pipes can be found by one of the three formulas:  Darcy-Weisbach Where, hf = head loss (m) f = friction factor (which is related to the relative roughness of the pipe material & the fluid flow characteristics) L = length of pipe (m) gD fLV hf 2 2 
157. 157.  Hazen-Williams formula Where, C = Coefficient that depends on the material and age of the pipe S = Hydraulic gradient (m/m) L h S S CD Q f   , 278 . 0 54 . 0 63 . 2
158. 158.  Table - Values of C for the Hazen-Williams formula Pipe Material C Asbestos Cement 140 Cast Iron  Cement lined  New, unlined  5years-old, unlined  20 years old, unlined 130 – 150 130 120 100 Concrete 130 Copper 130 - 140 Plastic 140 - 150 New welded Steel 120 New riveted Steel 100
159. 159.  Nomographs solve the equation for C = 100. Given any two of the parameters (Q, D, hf or V) the remaining can be determined from the intersections along a straight line drawn across the nomograph.  Manning’s Formula , R = D/4, S = hf/L n S AR Q 2 / 1 3 / 2 
160. 160.  Where, n = Coefficient of roughness depending on pipe material, usually n = 0.013 GI pipes n = 0.009  Plastic pipes n = 0.015  Clay concrete pipes
161. 161. Procedure of Analyzing Pipe Size and Pressure  Assume any internally consistent distribution of flow. The sum of the flows entering any junction must equal the sum of the flows leaving  Compute the head losses in each pipe by means of an equation or diagram. Conventionally, clockwise flows are positive and produce positive head losses.  With due attention to sign, compute the total head loss around each circuit: hL = KQn.  Compute, without regard to sign, for the same circuit, the sum of: KnQn-1.  Apply the corrections obtained from equation to the flow in each line. Lines common to two loops receive both corrections with due attention to sign.