Environmental Engineering-II Prof. Rajesh Bhagat

1. Environmental Engineering-II Prof. Rajesh Bhagat B.E. ( Civil Engg.) M. Tech. ( Enviro. Engg.) GCOE, Nagpur VNIT, Nagpur Experience &Achievement: Selected Scientist, NEERI-CSIR, Govt. ofIndia. GATE Qualified ThreeTimes. Selected Junior Engineer, ZPWashim. Three Times Selected as UGC Approved AssistantProfessor. Assistant Professor, P.C.E.,Nagpur. Assistant Professor, Cummins College of Engg. For Women (MKSSS, Nagpur) Topper of Pre-PhD Course Work at UGC-HRDC, RTMNU Nagpur Mobile No.:- 8483002277/8483003474Email ID:- rajeysh7bhagat@gmail.com Website:- www.rajeysh7bhagat.wordpress.com

2. UNIT-I Systems of sanitation: Conservancy and water carriage system. Patterns of sewage collectionsystems. Quantity of storm water and sanitarywastewater. Hydraulic Design of sewers - capacity, size, grade, shapes andmaterials. 2

3. References:- B.C. Punmia, Waste Water Engineering ( Vol. – II ), LaxmiPublication. S.K. Garg, Environmental Engineering ( Vol.– II), StandardPublication. G.S. Birdie, Water Supply & Sanitary Engineering, Dhanpat RaiPub. P. N. Modi, Sewage Treatment Disposal & Waste Water Engg. ( Vol. – II ), Standard Book House Pub., Delhi. M.N. Rao & H.V.N. Rao, Air Pollution, McGraw HillPublication. M.J. Machghee, Water Supply & Sewage, McGraw HillPublication.

4. Refuse: Anything rejected or left asworthless. (Solid & Liquid) Sullage: Wastewater from bath rooms, kitchens, etc. & does not include human or animal excreta. Sewage: Liquid waste from community & includes sullage, discharge from latrines, urinals, industrial wastewater & stormwater. SanitarySewage:Liquidwasteofdomestic&industrialplaces.Extremelyfoulinnature&required to be disposed off verycarefully. Sewer: Underground conduits or drains through which sewage is conveyed are known as sewers. Sewerage: The entire science of collecting and carrying sewageby water carriage system through sewers is known as sewerage. Sanitation: Science of preserving health of public & such condition which will prevent the outbreak of diseases dangerous for general health of public. Sanitary Engineering : Branch of Public Health Engg. which deals with all the aspects of provision of sanitation facilities. 25

5. Importance of SanitationSystem:- Spent water from bathroom, kitchens, basins, house washing, street washing, from industrial processes, semi liquid waste of human and animal excreta, dry refuse of houses, etc are produceddaily. If proper arrangement for collection, treatment & disposal of all waste produced are not made, they will go on accumulating & creates such foul condition that the safety of the structure such as building, roads will be in danger due to accumulation of wastewater in the foundation. The disease producing bacteria spread up in the stagnate water & the health of public will be indanger. All the drinkable water will bepolluted. Total insanitary conditions will be developed in thetown. It will be impossible for public to live in thecities. Therefore in the interest of community or society it is most essential to collect treat & dispose of all the waste products in such a way that it may not cause any havoc to the people residing in thetown. 11

7. Sanitation Work orSystem:- • Sanitary engineering starts at the point where water supply engineeringends. • The sanitary works can be broadly classifiedas: • CollectionWork • Transportation Work • TreatmentWork • Disposal Work • CollectionWork: • Collecting all types of waste products of thetown. • Refuse is collected separately & sewage is collectedseparately. • Collection work should be such that waste matter can be transported quickly & steadily to the treatmentplant. • Safe, efficient &economical. 12

8. TreatmentWork: • Sewage needs treatments before disposal so that it may not pollute the environment and waterbody. • If the wastewater is not treated it will cause many harms like pollution of water supply sources, destruction of food, fish and valuable aquatic life, creation of unpleasant sights & atmospheric air pollution,etc. • DisposalWork: • The treated or untreated wastewater are disposed off in various ways by irrigating fields or discharging into natural water course,etc. 13

9. Points are to be considered before finalizing a SanitationProject:- Financialaspects: Population: Quality ofsewage: Rainfall: Rate ofsewage: Sources ofsewage: Topography ofarea: Present method ofdisposal: TreatmentMethods: Trends of towndevelopment: 14

10. Site for Sewage TreatmentWorks:- Good foundation soil should be available for various units to rest firmly on theground. The general slope of the site should be moderate, so that flow from one unit to the othertake place by gravityonly. Site should be lowest level area of the town, so that sewage from entire town canbe collected by gravityonly. Enough area is available for futureexpansion. Safe fromflood. Site should be situated on the leeward side ofwind. Not far way fromcity. Subsoil water level at the site should be remain low even duringmonsoon. 15

11. Sewage or Wastewater: Used water or liquid waste generated by the community due to its variousactivities. Any water or liquid that contains impurities in such a concentration that isharmful if disposed into theenvironment. It is 99.9% water & 0.1%solids Quantity of sewage = 75 to 80 % of the watersupplied Lesser the supply of water greater the strength &vice-versa. 16

12. TYPES OF WASTEWATER DEPENDING ON SOURCE OFGENERATION • Domesticwastewater: • the used water from the residential, commercial, & institutional zones of acity. • partially treated wastewater from small industries are alsoincluded • Industrialwastewater: • the liquid waste from large & medium scaleindustries. • vary in quantity andquality • large volume & highstrength 17

13. Collection System or Methods: ConservancySystem Water-CarriageSystem 19

14. ConservancySystem: • Prevailing in small town or undevelopedtowns. • Various types of refuse & storm water are collected, conveyed & disposed off separately by different methods therefore it is called conservancysystem. • In the past, disposal of waste from water closets was carried out manually (dry System) and wastewater generated from kitchen and bathrooms was allowed to flow along the opendrains. • Human excreta is collected separately in privies or conservancylatrines. • The liquid & semi-liquid waste are collected in separate drains of the same latrines, from where they are removed through humanagency. • After removal night soil is taken outside the town in closed animal drawn carts ortrucks. • Cheaper in initialcost. • Aesthetic appearance of city can not beincreased. 20

15. Water-CarriageSystem: • With the development & advancement, urgent need was felt to replace conservancy system with improved type of system, in which human agency should not be used for the collection & conveyance of thesewage. • Wateristhecheapestsubstanceusedtotransportthesewageeasily&effectivelytherefore • it is called water-carriagesystem. • Excremental matter are mixed up in large quantity water & are taken out from the city through properly designed sewerage system., where they are disposed off after necessary treatment. • Initial cost & maintenance cost ismore. 21

16. Water-CarriageSystem: • The old system may pose the health hazards, because of the possibilities of flies and insects transmitting disease germs. This is avoided in new system because of transport of night soil in close conduit. The human excreta is washed away as soon as it is produced, thus storing is not required as required in the old system of manualdisposal. • In the old system, the wastewater generated from the kitchen and bathrooms was required to be carried through open roadside drains for disposal. This is avoided in sewerage system as the open drains could generate bad odor when used for disposal of organicwaste. • The water carriage system does not occupy floor area, as the sewers are laidunderground. • Constructionoftoiletsoneabovetheotherispossibleinwatercarriagesystemand • combining latrine and bathrooms together as water closets ispossible. 22

17. Advantages of Water-CarriageSystem: • It is hygienicmethod. • No human agency isemployed. • There is no nuisance & risk of epidemics isless. • It occupies less space in crowdedlane. • Due to more quantity of sewage, self cleansing velocity can be obtained even at less gradient. • Building can be designed compact as oneunit. • Less area is required fordisposal. • The usual water supply is sufficient & no additional water isrequired. • This system does not depend on manual labor everytime. • Sewage after proper treatment can be used for variouspurposes. 23

19. SewerageSystem or Water Carriage System: • The sewerage system are classified asfollows: • CombinedSystem • SeparateSystem • Partially SeparateSystem • Combinedsystem: • Only one set of sewers is used to carry both the sanitary & stormwater. • Most suited in areas having small & evenly distributed rainfall throughout theyear. • In India, this system will face the problem of maintaining self cleansing velocity in the sewers during dryseason. • Noneedofflushingbecausemoreselfcleansingvelocityisavailableduetomorequantity • ofsewage. • Rain water dilutes thesewage. • Initial cost is high as compared with separatesystem. • In congested areas, easy to lay one large sewer than two smallersewers. • 26

20. Advantages of CombinedSystem: • Where rainfall is spread throughout a year, there is no need of flushing of sewers, as self cleansing velocity will developed due to more quantity because of addition of storm water. • Only one set of pipe will be required for houseplumbing. • In congested areas it is easy to lay only one pipe rather than two pipes as required in othersystems. • Disadvantages of CombinedSystem: • Not suitable for the area with small period of rainfall in a year, because dry weather flow will be small due to which self cleansing velocity may not develop in sewers, resulting in silting. • Large flow is required to be treated at sewage treatment plant before disposal, hence resulting in higher capital and operating cost of the treatmentplant. • When pumping is required this system isuneconomical. • During rains overflowing of sewers will spoil or endanger publichealth. 27

21. SeparateSystem: • Two sets of sewers are used, one for carrying sewage & other for carrying stormwater. • Sewage is carried to the treatment plant & storm water is discharged directly into natural outlet. • Advantages: • Load on treatment units becomesless. • Natural water (Storm Water)is not unnecessarilypolluted. • Small size sewers arerequired. • Storm water discharged into naturalstreams. • Economical when pumping is needed for lifting ofsewage. • Disadvantages: • Cleaning of sewer are difficult as they are small insize. • Maintenance cost ishigh. • Self cleansing velocity is not easily achieved due to small quantity ofsewage. • Storm water sewers operates only during monsoon hence becomes dumping placefor garbage during summer-winter& may thus bechoked. 28

22. Partially SeparateSystem: 1) Part of the storm water especially collected from roofs and paved courtyards of the buildings is admitted in the same sewer along with sewage from residences and institutions, etc. The storm water from the other places is collected separately using separateconduits. Advantages: Economical and reasonable size sewers arerequired. Work of house plumbing is reduced as rain water from roofs, sullage from baths and kitchen, etc. are combined with discharge from waterclosets. Flushing of sewers may not be required as small portion of storm water is allowed to enter in sanitarysewage. Disadvantages: The quantity of storm water admitted in sewer may increase the load on pumping and treatmentunits. Self-cleansing velocity may not develop in the sewers in dryweather. 29

24. Patterns of CollectionSystem: PerpendicularPattern InterceptorPattern RadialPattern Fanpattern ZonalPattern The patterns of collection system dependupon: The topographical and hydrological features of thearea. The location and methods of treatment and disposalworks. The type of sewerage system employed,and Extent of area to beserved. 31

25. 1) Perpendicularpattern: • The main trunk sewer are laid perpendicular to natural watercourse. • The shortest possible path is maintained for the rains carrying storm water andsewage. • Suitable for separate system and partially separatesystem. • Not suitable for combined system, because treatment plant is required to be installed at every point of outlet; otherwise it will pollute the water body where the sewage is discharged. di laratt 32

26. 2) Interceptorpattern: • Improvement over the perpendicularpattern. • Sewers are intercepted with large size sewers which are laid along the watercourse. • Interceptor carries sewage to a common point, where it can be disposed off with or without treatment. • Overflow or Storm regulators may be provided to handle very large flow or stormwater. Fig.1.2InterceptorPattern(1)

27. 3) RadialPattern: • Sewers are laid radially outwards from the centre of city, hence this pattern is called as radialpattern. • It is suitable for sewage disposal byland. • More number of disposal works isrequired. Radial Pattern(1) 34

28. 4) FanPattern: • Single treatment plant is located at a certain common point & the entire sewage flow is directed towards thispoint. • Suitable for a city situated at one side of the natural water body, such asriver. • Number of converging main sewers and sub-mains are used forming a fanshape. • The drawback in this pattern is that larger diameter sewer is required near to the treatment plant as entire sewage is collected at commonpoint. • For new development of the city the load on existing treatment plant increases hence restriction will have to be imposed on suchdevelopment.. Fig.1.4FanPattern(3) 35

29. 5) ZonePattern: • City is divided into suitable zones and separate interceptor is provided for eachzone. • More numbers of interceptors are provided in thispattern. • Suitable & economical for sloping area than flatareas. n 36

30. Factors to be Considered in the Determination of the Quantity of StormWater: • Intensity & Duration ofRainfall: • Topography ofWatershed: • Extent of CatchmentArea: • Shape of theArea: • Slope of theArea: • Nature ofSoil: • Number of Available Ditches in theArea: • Atmospheric Temperature, Wind &Humidity:

31. StormWater: The quantity of storm water can be calculated by following two methods Rational &Empirical Formulae: RationalMethod: Q = ( Ax Cx R) /360 Q = Quantity of storm water inm3/s R = Intensity of rainfall, mm/hour A = Drainage area inhectors C = Runoff coefficient, 0.1 -0.95 Overall runoff coefficient for different types of surfacearea, C = ((A1 x C1 + A2 x C2 + …. +An x Cn) / (A1 + A2 +…. +An)) A1, A2, An are the different area & C1,C2, Cn are their runoff coeff.Respectively.

32. StormWater: The quantity of storm water can be calculated by two methods Rational &EmpiricalFormulae: Empirical FormulaeMethod: All empirical formulae are only applicable under certain condition. Suitable for aparticular region after long practical, experience & collection ofdata. Burkli- Zeiglar Formula: Q = (( C I A)/141.58)4√(S/A) McMath’s Formula: Q = (( C I A)/141.58)5√(S/A) Fuller’s Formula: Q = C M 0.8 /13.23 Fanning’s Formula: Q = 12.8 M5/8 Talbot’s Formula: Q = 22.4 M¼ Q = Runoff inm3/s I = Intensity of rainfall, cm/hr ( R = rainfall intensity) S = Slope of the area, meter per thousandmeter A = Drainage area in Hectors & M = Drainage area inKm2C = Runoff coefficient or I = ImpermeabilityFactor

33. Dry Weather Flow: DWF • The sewage consists of DWF and Storm water. • DWF is the flow through the sewer that would be available through out the year, that is during non-rainy season. • DWF includes domestic sewage, industrial sewage & groundwater infiltration. • DWF depends on water supply rate, population growth, area served, type of area, infiltration & exfiltration.

34. Quantity of SanitarySewage: The quantity of sanitary sewage is mainly affected by the followingfactors: Rate of watersupply Population Type of area served as residential, commercial, industrial,etc. Ground waterinfiltration. Determination: Quantity of sanitary sewage should be equal to the quantity of water applied by water works but actually subtraction are done due to leakage or water being consumed indrinking, cooking, sprinkling,etc.After doing all calculation, addition & subtraction, Quantity of sanitary sewage = 75 to80% of the total watersupplied.

35. Variation in Quantity of SanitarySewage: Practical average never flow in sewer, it continuously varies from hour to hour of theday and season toseason. The design of sewer should be done for the maximum possibleflow. Fluctuation is due to outcome certain local condition, habits, customs, holidays, season,etc. Self cleansing velocity should be maintained in the case of minimumflow.

36. Maximum DailyFlow = Two times the annual average dailyflow Maximum Hourly Flow = 1.5 times the maximum dailyflow (accounting hourlyvariations) = Three times the annual average dailyflow = 2/3 Annual average dailyflow Minimum dailyflow Minimum hourlyflow = ½ Minimum dailyflow = 1/3 Annual average dailyflow

37. Self Cleansing Velocity: • Sewer should be designed that the solid matter present in the sewage is not deposited at the bottom of the sewer and thus clogging of the sewer is prevented. • The deposition of solid matter and resulting clogging of the sewer can be prevented if the solid matter is held in suspension in the flowing sewage. • In order to keep the solid matter in suspension certain minimum velocity of the flow of sewage is required. • Such a minimum velocity of flow is known as self cleansing velocity. • The minimum velocity of flow at which the solid particles present in the sewage will be held in suspension and also at which the scour of the deposited particles will takes place so that sewer will be kept clean.

38. DesignPeriod Thefutureperiodforwhichtheprovisionismadeindesigningthecapacitiesofthe variouscomponentsofthesewerageschemeisknownasthedesignperiod. The design period depends upon thefollowing: Ease anddifficulty in expansion, Amount andavailability of investment, Anticipatedrateofpopulationgrowth,includingshiftsincommunities,industries and commercialinvestments, Hydraulicconstraintsofsystemsdesigned,and Lifeofmaterialandequipment. Laterals less than 15 cm diameter : Fulldevelopment Trunk or main sewers : 40 to 50years Treatment Units : 15 to 20years Pumping Plant : 5 to 10years

39. Important Factors Considered for SelectingMaterialforSewer :Resistance tocorrosionResistance toabrasionStrength anddurabilityWeight of thematerialImperviousnessEconomy andcostHydraulicallyefficient Materials forSewers : Asbestos Cement Sewer Plain Cement Concrete RCC Vitrified Clay or Stoneware Sewers Brick Sewers Cast Iron Sewer Steel Pipe Sewer Ductile Iron Pipes Plastic Sewers or PVC Pipe

40. Surface DrainSection: Rectangular SurfaceDrain Semicircular SurfaceDrain U-Shaped SurfaceDrain V-Shaped SurfaceDrain

41. Shapes of SewerPipes (a) Standard Egg ShapedSewer ( b) New/ Modified Egg shapedSewer Fig. Shapes ofSewer (c) Horse shoe sewersection (d) Parabolicsection

42. (e) Semi-ellipticalsection ( f) RectangularSewer (i) Basket-HandleSection Fig. Shapes ofSewer (h) Semi-circularSection (g) U-shapedsection

43. Egg ShapedSewer:- Thedepthoftheseseweris1.5mtimesoftheirwidth. Constructed at site & made of concrete and brick arch with special invert at bottom ofRCC. Betterhydraulicpropertythancircularwithlowdischarge. Usedinbothcombined&separatesystem. MostsuitableforcombinedsystembcozgivesselfcleansingvelocityeveninDWF. Equally suitable for separatesystembcozeasily accommodate the flow of sewage withthedevelopmentofthetown. Disadvantages are construction is difficult, less stable &requires good masonary backing.

44. Que. 1Calculate the velocity of flow in a sewer of diameter 1.5m. The sewer is laid at a gradient of 1 in 550m. What will be the discharge through this sewer when running one-half full? Assume m = 0.012 in Manningsformula. According to Manning’s formula v = (1 / m) x r(2/3) xS(1/2) Hydraulic Mean Depth, r = (A/P) = d/4 for circular sewer running one halffull r = 1.5 / 4 =0.375m S = slope or gradient = 1 / 550 Putting values in Manning’sformula, v = (1/0.012) 0.375(2/3)(1/550)(1/2) v = 1.84m/s Q = A xv Q = ½ x ((∏ x d2) / 4 ) x(1.84) Q = 1.63 m3 /s

45. Que.2Determinethevelocityofflowinacircularsewerdiameter120cm,laid on slope of 1 in 700, while flowing full. Assume m = 0.013 in Manning’s Formula. r =0.3 m v = 1.302 m/s Q = 1.47m3/s

46. Que. 3A sewer district has the Area = 5 hectors, Impermeability factors = 0.5, Design intensity of rainfall = 40 mm/hr, Density of population = 500 person per hectors, Average rate of water supply = 200lpcd.Determine the sanitary sewage and storm water flow for design ofsewer. Sanitary SewageFlow: Average rate of water flow = 200lpcd Assuming peak factor =3 Area, A = 5hector Population Density, Pd = 500 person perhector Q = 3 x A x Pd x flowrate Q = 3 x 5 x 500 x200 Q = 1.5 x 10 6 Lit/Day Q = 0.0174 m3 /sStrom WaterFlow: Q = (A x C x R) /360 Q = (5 x 0.5 x 40) / 360 = 0.278 m3 /s Note: Sewage Flow is less than Storm water Flow.

47. Que. 4Design the section of a combined circular sewer when area to be served = 150 hectares, population of locality = 50000, Max permissible velocity = 3.2 m/s, time ofentry = 5 minutes, time of flow = 20 minutes, Rate of water supply = 270 liters/day/capita & Impermeability factor =0.45. Sanitary SewageFlow: Assuming peak factor =3.0 Maximum Sewage flow, Q = (3.0 x 270 x 50000 x 10-3 ) / (24 x 60 x 60) = 0.4687 m3 /s Strom WaterFlow: Time of Concentration = 5 + 20 = 25Minutes Intensity of Rainfall, R = ( a / (t +b)) when time of conc. 21to 100 minutes, a=1016& b=20 R = (1016/ (25 + 20)) = 22.58mm/hr Q = (A x C x R) /360 Q = (150 x 0.45 x 22.58) / 360 = 4.23m3 /s Combined Discharge = 0.4687 + 4.23= 4.6987 m3 /s Q = Axv A = Q/v A = 4.6987/ 3.2 = 1.468m2 Diameter of sewer, D = √((A x 4) / ∏ ) =1.35m

48. Que. 5Design a storm sewer when area to be distributed = 5 hectors, effective impermeability factor = 0.4 & time of concentration = 20 minutes. Determine size and grade of the sewer if velocity is to be maintained 1 m/s. Rainfall intensity is givenby R = (a) / ( b +t) Take a = 750, b = 10 & m =0.015. Strom WaterFlow: Time of Concentration = 20 Minutes Intensity of Rainfall, R = (a) / ( b + t) R = (750/ (10 + 20)) = 25mm/hr Q = (A x C x R) /360 Q = (5 x 0.4 x 25) / 360 = 0.14m3 /s Q = Axv A = Q/v A = 0.14/ 1 = 0.14m2 Diameter of sewer, D = √((A x 4) / ∏ ) = 0.42m According to Manning’s formula v = (1 / m) x r(2/3) xS(1/2) v = (1 / 0.015) x (D/4)(2/3) xS(1/2) 1 = (1 / 0.015) x (0.42/4)(2/3) xS(1/2) S = 4.6 x10-3 1 in220m

49. Que. 6 A small town with a projected population of 30,000 residing over an area of 16 hectors is provided with a water supply @ 150 lpcd. Find the design discharge for a combined sewer . Assume runoff coefficient = 0.4 and time of concentration = 15 minutes. Make suitable assumption where needed. ( P. N. Modi) Sanitary SewageFlow: Assuming peak factor =3.0 & Sewage flow will be 80 % of water supplied. Maximum Sewage flow, Q = (3.0 x 0.8 x 150 x 30000 x 10-3 ) / (24 x 60 x 60) = 0.125 m3 /s Strom WaterFlow: Time of Concentration = 15Minutes Intensity of Rainfall, R = ( a / (t +b)) when time of conc. 5 to 20 minutes, a=762 & b=10 R = (762 / (15 + 10)) = 30.48 mm/hr Q = (A x C x R) /360 Q = (16 x 0.4 x 30.48 ) / 360 = 0.54 m3 /s Combined Discharge = 0.125 + 0.54 = 0.665 m3/s