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Population Dynamics

Population Dynamics. Perspective. Definition – the study of the changes in the numbers and composition of individuals in a population within a study unit and the factors that affect these numbers Can involve any organism or group of organisms

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Population Dynamics

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  1. Population Dynamics

  2. Perspective • Definition – the study of the changes in the numbers and composition of individuals in a population within a study unit and the factors that affect these numbers • Can involve any organism or group of organisms • Study unit can be any biological, geographical, political or engineered area

  3. Bacterial Growth Requirements • Macronutrients a. carbon b. nitrogen c. phosphorus • Micronutrients a. trace metals b. vitamins • Environment a. moisture b. temperature c. pH

  4. Growth in Pure Cultures

  5. Mathematics of Growth • log growth phase

  6. Example • Bread yeast cells divide and form 2 cells every 5 minutes. If you place 105 cells in a suitable environment, how many cells will you have in 30 minutes?

  7. Mixed Cultures • Pure cultures do not exist in nature • Log growth may occur when one organism or group has few external limits • Most organisms interact with other organisms: • competition for food and other resources • disease • induced changes in environment

  8. Human Population Dynamics • Exponential model is commonly used, but this may be an issue of time scales where b = birth rate d = death rate i = immigration rate m = emigration rate

  9. Sewerage Systems

  10. SOME BASIC TERMS SEWAGE: - It is the liquid waste or wastewater produced as a result water use SEWER: - It is a pipe or conduct for carrying sewage. It is generally closed and flow takes place under gravity SEWERAGE:- It is a comprehensive term. This term is applied to the ART OF the collection of wastewater and conveying it to the point of final disposal with or without treatment

  11. SOURCES OF WASTEWATER • DOMESTIC: It is wastewater from residential buildings, offices, other buildings and institutions etc • INDUSTRIAL: It is liquid wastewater from industrial processes like dying, papermaking, fertilizers, chemicals lather etc • STROMWATER: It include surface run off generated by rainfalls and street wash

  12. DISPOSAL OF WASTEMATERIAL ON LAND AND WATER BODIES • Liquid wastes may be disposed of in a number of ways (before giving at least secondary level treatment) • -Surface waters (Rivers, Lakes etc) • -On land

  13. TYPES OF SEWERS • Sanitary Sewer: Sewer which carries sanitary sewage i.e. Wastewater originating from a municipality including DOMESTIC and INDUSTRIAL Wastewater. • Storm Sewer: It carries storm sewage including surface runoff and street washes. • Combined Sewer: It carries domestic, industrial and storm sewage. • House Sewer: Pipe conveying sewage from plumbing system of a building to common / municipal sewer.

  14. TYPES OF SEWERS • Lateral Sewer: It receive discharge from house sewer. • Submain Sewer: It receive discharge from one or more laterals. • Main / Trunk Sewer: Receive discharge from two or more submains. • Outfall Sewer: Receive discharge from all collecting system and convey it to the point of final disposal (e.g. Water Body).

  15. COMPONENTS OF WASTE WATER ENGINEERING • Collection system • Disposal works • Treatment works

  16. TYPES OF SEWEARAGE SYSTEMS • Separate system:- If storm water is carried separately from domestic and industrial waste, the system is called separate system. • When Favoured:- There is an immediate need for collection of sanitary sewage but not for storm sewage. • Combined system:- A system in which sewer carry both sanitary as well as storm sewage. • When favoured:- • When combined sewage can be disposed off without treatment • When both need treatment. • When streets are narrow and two separate sewerage cannot be laid.

  17. TYPES OF SEWEARAGE SYSTEMS • Partially combined: If some portion of storm or surface runoff (from roof, roads, open spaces etc) is allowed to be carried along with sanitary sewage, the system is know as partial combined system. Note:-In urban areas mostly partially combined system is used:- Domestic Wastewater + Rain Water Municipal Sewers Street

  18. INFILTRATION • It is the water that enters sewer through poor joints, cracked piped and walls and covers of manholes. Infiltration is almost non-existent in dry weather but it will increase during rainy seasons. In dry season if sewer is below water table infiltration will take place. • Infiltration rates > 45 lit/Km of sewers / day / mm dia (EW Steel) • WASA: - 225mm – 610mm Infilt = 5% of Avg Sewage flow • > 610 mm = 10% of Avg Sewage flow

  19. Infiltration Pump Pump 16’ 12’ GWT 4’

  20. SEWAGE FLOW / QUANTITY • Sanitary and industrial sewage is derived from water supply so it has a relationship with amount of water consumption. Generally 80 ~ 90% of water consumption is taken as wastewater.

  21. VARIATION IN SEWAGE FLOW • Like water supply flow varies from time to time. Since sewers must be able to accommodates the max flow the variation in sewage flow need to be studied. • Generally following formula is used to estimate the ratio (Peak factor) of max to average flow. • Qmax = M = 1 + 14/(4 + P) (E.W Steel) Where • P = Population in Thousand • M = Peak factor • Some Engrs use 22 as numerator

  22. WASA Criteria • Av flow (m/d) Peak Factor • < 2500 4.0 • 2500 ~ 5000 3.4 • 5000 ~ 10000 3.1 • 25000 ~ 50000 2.7 • 50000 ~ 100000 2.5 • 100000 ~ 250000 2.3 • 250000~ 500000 2.15 • > 500000 2.08 • Significance of Avg. or min flows: Used in design of sewage pumping stations. Used to investigate velocities in sewers during low flow period.

  23. Problem The residential area of a city has a population density of 15000 persons / square Km and an area of 120000 Sq. m. If average water consumption is 400 lpcd. Find the average and maximum sewage flow in Cub. m / day.

  24. Solution • Pop. Density = 15000 per / km2 • Area = 120000 m2 • Avg. Water Consumption= 400 lpcd • Total population = 15000 x 120000 / (1000)2 = 1800 persons • Avg. Sewage flow = 1800 x 400 x 80/100 = 576000 l/day = 576 m3/day

  25. Maximum Sewage Flow Peak factor: M = 1 + 14/(4 +P) (in thousands) M = 1 + 14/(4 +1.85) = 3.62 Max sewage flow = 3.62 x 576 = 2.85 m3/day

  26. DESIGN PERIODS • Collection works. Period of design is “INDEFINATE” as the system is designed to care for the maximum development of the area. Design flow depend on type of system. • 2. DISPOSAL WORKS. Design period is usually 10 years. Rates of flow required are average flow, peak and minimum flow rates including infiltration.

  27. DESIGN PERIODS • TREATMENT WORKS. Design period is 15 to 20 years. Flow rates required are average and peak rates both including infiltration

  28. INVERT LEVEL • INVERT LEVEL. It is the level of the INVERT of the sewer pipe. • Invert: Inverted arch • Invert level= G.L – Cover over pipe – Thickness of Pipe – Dia of pipe. Cover Over Pipe Invert level

  29. STEPS FOR DESIGN OF SEWER • Preliminary Investigation • Design consideration / formulation of design criteria • Actual design • Preparation of drawing and BOQ • Subsequent modifications.

  30. PRELIMINARY INVESTIGATION It includes: - • If map of the area is not already available the first step is to carry out survey to draw the map of project area. Different details are marked on the map like • Streets • Railway Lines • Streams • Locations of under ground utilities like gas, waster mains etc. • Establish benchmarks throughout the area and make down profiles.

  31. PRELIMINARY INVESTIGATION • Soil conditions should be investigated for the type of stratum, location of water table, presence of any underground rock etc. • Collection of rainfall. • Study of the natural slopes of area and selection of suitable disposal point.

  32. DESIGN CONSIDERATIONS / FORMULATIONS OF DESIGN CRITERIA • Design Flow Sanitary sewer = Peak flow + infiltration + Industrial flow Partially combined = 2 x peak sewage flow + infiltration + Industrial. (WAS criteria)

  33. Design Equation • Design Equation Sewers are designed on the basis of open channel flow. V = 1/n R2/3 S ½ (Manning's Formula) Where, V = Velocity, m/s R = Hydraulic mean depth = Area / wetted perimeter = D/4, when pipe is flowing full S = Slope of sewer n = Coefficient of roughness

  34. Minimum Velocities • Min Velocities Min velocities are called cleansing velocities must be maintained in sewers to avoid deposition of suspended solids and subsequent chocking solids of sewers. Sanitary Sewers = 0.6 m/s (Organic Particular S.G = 1.61) Storm Sewers = 1 m/s (Inorganic particulars S.G = 2.65) Partially Combined = 0.7 m/s

  35. Max Velocities • Max Velocities < 2.4 m (EW Steel) A limit on higher velocity is imposed due to abrasive character of solids in wastewater. Other reason is that there will be higher slope of sewer and result in more execution. In likely areas we have to provide more slope due to natural slopes.

  36. Minimum Size of Sewer • Minimum Size 225mm is taken as min size (WASA, PHED) (Water and Sanitation Agency, Public Health Engg. Deptt.) • Minimum Cover 1m is taken as min cover over sewers to avoid damage from live loads coming on sewers.

  37. Manholes • Manholes Purpose: 1. Cleaning 2. Inspection 3. House Connections Where provided: • At every change in direction • Where two different dia. pipes are to be connected • At junction of pipes

  38. Manhole Spacing Spacing: Dia of Sewer Manhole Spacing 9” – 15”(225mm – 380mm) >! 100m 18” – 24” (460mm – 760mm) >! 120m >24” (> 760mm) >!150m Note: For plots, one manhole be provided for 2 plots.

  39. Qd/Qf Ratio WASA recommended the Qd/Qf ratio in order to provide air space in the upper portion of sewer for ventilation purpose. Qd represent design flow and Qf is flow when sewer is flowing full. Sewer Size Ratio(Qd/Qf) 225 – 380 mm 0.7 460 – 1220 mm 0.75 1370mm and above 0.8

  40. DWESIGN OF SEWER DWESIGN OF SEWER: By design of sewer, we mean the following two things. • a.To find SIZE of sewer Q=AV is used to find size. • b.To find required SLOPE to maintain a minimum velocity in sewers. V = 1/n R2/3 S1/2 is used to find slope

  41. PREPARATION OF DRAWINGS AND BOQ PREPARATION OF DRAWINGS AND BOQ: Typical drawings include: • ·Sewer points • ·Manholes • ·Disposal Station • ·Sewer profiles or L-Sections SUBSEQUENT MODIFICATIONS: • Mostly done due to some unforeseen incident, to accommodate some additional demand / requirement of the client etc. there may be several other reasons.

  42. PROBLEM Calculate the size and slope of a sanitary trunk sewer serving a population of 0.4 million. Water consumption is estimated to be 300 lpcd. Pipe used is RCC. Take infiltration as 10% of average sewage flow.

  43. Solution Population = 0.4 x 1000000 x 300 = 120000 m3 / day = 1.388 m3 / sec Dry weather flow: Design flow = peak flow Minimum Flow = Average flow Average Sewer flow = 1.388 x 80/100 = 1.11 m3 / sec = 96000 m3 / day Peak Factor (WASA) = 2.3 Peak Flow = 2.3 x 96000 = 220800 m3 / day

  44. Infiltration = 10/100 x 96000 = 9600 m3 / day Design Flow = Peak Flow + infiltration = 220800 + 9600 =230400 m3 / day = 2.67 m3 / sec Dia of sewer: Q = AV 230400 x 1 / 24 x 60 x 60 = A x 0.6 A = 4.45 m2 Dia = 2.38 m Slope of sewer: V = 1/n R2/3 S1/2 0.6 = 1/0.013 x (2.38/4) 2/3 (S)1/2 S = 1.2157 x 10-4 S = 0.0001215 mm

  45. PROBLEM A 225 mm sewer is to flow full at velocity of 0.75 m/s • A: What is its maximum capacity and what minimum grade it should be laid if coefficient of roughness is 0.013. How many people it can serve if the average per capita flow is 300 lpcd. Ignore infiltration • B: How many additional people the sewer can cater if slope is doubled.

  46. SOLUTION Maximum Capacity: Q = A.V Q = /4 x (225/1000)2 x 0.75 Q = 29.82 l/s = 2576 m3/day Slope using Manning’s Equation V=1/n R2/3 S½ 0.75=1/0.013 (0.225/4)2/3 S ½ S=0.0044

  47. No. of Persons Q = 2576 m3/day = Design flow Avg flow = 300 lpcd Discharge = lpcd x persons 2576 x 1000 = 300 x persons No. of persons = 8586

  48. When Slope is doubled B. Slope is doubled: S = 2 x 0.0044= 0.0088 V = 1/0.013 (0.225/4)2/3 (0.0088)1/2 V = 1.059 m/s Q = AV = /4 x (0.225)2 x 1.059 Q = 0.04212 m3/s = 3639 m3/day Persons = 3639 x 1000 / 300 Persons = 12130 persons Additional persons = 3544

  49. HYDRAULIC STATEMENT It is a table of calculations on for the design of SEWERS.

  50. SEWER FLOWING PARTIALY FULL It is necessary to determine velocity and depth of sewage in a pipe when it is flowing only partially full. For this, use of the graph will allow quick computation of the hydraulic elements of partially filled circular sewer. For using this graph, it is necessary to find first the conditions when a sewer is flowing full. Then by calculating the ratio of any two known hydraulic elements, the others can be found.

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