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Environmental engineering 2 1st unit


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Environmental engineering 2 1st unit

  1. 1. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHENVIORNMENTAL ENGINEERING-IIUNIT – IPlanning for Sewarage SystemsPART – A1. What are the types of treatment processes?1) Preliminary treatment2) Primary treatment3) Complete final treatment4) Secondary treatment2. What are the various sources of wastewatergeneration?I. Industrial WastesII. Domestic wastesIII.Agricultural Wastes3. List out the types of anaerobic bio logical units?1. Anaerobic lagoons2. Septic tank3. Inhofe tank4. What is means by screening?Screening is the very first operation carried out ata sewage treatment plant and consists of passing thesewage through different types of screens so as to trapand remove the floating matter such as process of cloth,paper, wood, cork, hair, fiber etc.5. What is the purpose of providing screen?The main idea of providing screens is to protectthe pumps and other equipments from the possibledamages due to the floating matter of the sewage.It should be used for removing the floatingmatters.6. What are the types of screen?Classification based on size of the opening1. Coarse screens2. Medium screens3. Fore screensFilters AerationtanglesExudation ponds&Aerated
  2. 2. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHBased on shape7. Define bar screen?Rectangular shaped coarse and medium screensare made of steel bars fixed parallel to one another atdesired spacing on a rectangular frame and are calledbar screen.8. What is meat by movable screen?Movable screens are stationary during theiroperating periods. But they can be lifted up bodily andremoved from their partitions for the purpose of cleaning.A common movable bar medium screen is a 3 –sided cage with a bottom of perforated plates. It ismainly used in deep pits ahead of pumps.9. Define Communicators?Comminutes or shredders are the patenteddevices, which break the larger sewage solids to about 6mm in size. When the sewage is screened through themsuch devices are used only in developed countries likeUSA.10. What is meant by Screening?The material separated by screens is called thescreenings. It contains 85 to 90% of mixture and otherfloating matter. It may also contain some organic loadwhich may putrefy, lacing bad smells and nuisance.11. What are the methods adopted for disposal ofscreenings?1) Burning2) Burial3) DumpingBurning of the screenings is done in the incineratorsBurial: The process is technically called compostingAnother method of disposing of the screening is bydumping them in low lying areas (away from theresidential areas) or in large bodies of water such as sea.12. Define Grit Chamber?Grit chambers, also called or grit channels or gritbasins, are intended to remove the inorganic particles(specific graving about 2.65) such as sand, graver, grit,egg, shells, bones etc of size 2 mm or larger to preventdamager to the pumps and to prevent their accumulationin sludge digesters.Rectangular for coarse andmedium screensDisc or Drum for fore
  3. 3. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECH13. Define unit process?Methods of treatment in which the application ofphysical forces predominate are known as unitoperations while methods of treatment in which chemicalor biological activities are involved are known as unitprocess.14. What are the types of unit operations &processes?1. Physical unit operations2. Chemical unit process3. Biological unit process15. Give any two advantages of unit operations/process?1. It gives better understanding of the process asinherent in the treatment and of the capabilities ofthese processes in attaining the objectives.2. It helps in the development of mathematical andphysical models of treatment mechanisms and theconsequent design of treatment plants.16. Define phase transfer?Most waste water treatment process bring aboutchanges on concentration of a specific substances bymoving the substance either into or unit of the wastewater it self. This is called phase transfer.17. Define definition time?The definition time (t) of a settling tank may bedefined as the average theoretical time required for thesewage to flow through the tank. Otherwise known asdefinition period or retention period18. Define the term Displacement efficiency?The ratio of the “Flowing through period” to the“detention period” is called the displacement efficiency.19. What is meant by principle of sedimentation?The turbulence is retarded by offering storage tosewage these impurities tend to settle down at thebottom of the tank offering such storage. This is theprinciple of sedimentation.20. Define the term “Sedimentation Burin”?The burin in which the flow of sewage is retardedis called the settling tank or the sedimentation Tank orthe sedimentation Burin.21. Define the term “Detention Period”?The theoretical average time for which the water isdetained is called the detention period.22. Give any two advantage of chemical coagulationprocess in sewage treatment?
  4. 4. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHi) Sedimentation aided with coagulationproduces better efficient with lesserBOD and suspended solids, ascompared to plain sedimentation.ii) Coagulated settling tank requires lessspace than that required by an ordinaryplain settling tank.23. What are the Demerits of coagulation in sewagetreatment?i) Cost of chemicals is added to the cost ofsedimentation, with out much use, and therebymaking the treatment costlier.ii) The process of coagulation requires skilledsupervision and handling of chemicals.24. What are the types of sedimentation tank?Based on flow1. Vertical flow tank2. Horizontal flow tank3. Radial flow tankAccording to use1. Primary2. Secondary3. inter mediate25. What are the chemical used for precipitation ofsediment?1. Alum2. Ferrous sulphate3. Ferric sulphate4. Ferric chlorides5. Sodium alluminate6. Sulphuric acid7. lime8. copperas26. What are the factors that affect theprecipitations?1. Kind of chemical2. Quality of chemical3. character and concentration of sewage4. Ph values of sewage5. time of mixing and flowlations6. Temperature7. Violence of agitation27. What are the merits of chemical precipitation?(i) More rapid and through clarification(ii) Removal of higher percentage of suspendedsolids.(iii) Simplicity of operation(iv) Small size tank is
  5. 5. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHPART – B1. Explain classification of Treatment processes?Sewage before being disposed of either in riverstreams or on land has generally to be treated. So as tomake it safeSewage can be treated in difference waystreatment process are often classified as1) Preliminary treatment2) Primary treatment3) Secondary or (biological) treatment4) Complete final treatmentPreliminary treatment:Preliminary treatment consists solely in separatingthe floating materials (Like dead animals, tree branches,papers, pieces of rags, wood etc) and also the heavysettle able inorganic solids.It also helps in removing the oils and greases etc.From the sewage this treatment reduces the BOD of thewaste water, by about 15 to 30%.The process used are screening for removingfloating papers, rags, clothes etc.Grit chambers or detritus tanks: For removing grit andsandSlimming tanks: For removing oils and greases.Primary TreatmentPrimary treatment consists in removing largesuspended organic solids. This is usually this is usuallyaccomplished by sedimentation on settling basins.The liquid effluent from primary treatment oftencontains a large amount of suspended organic materialand has a high BOD about (60% of original).The original solids which are separated out in thesedimentation tanks (in primary treatment) are oftenstabilized by an anaerobic decomposition in a digestiontanks or are incinerated.Sometimes the preliminary as well as primarytreatments are classified to gather under primarytreatment.Secondary treatmentSecondary treatment involves further treatment ofthe efficient, coming from the primary sedimentation tank.This is generally accomplished through biologicaldecomposition of organic matter, which can be carriedout either under aerobic or anaerobic conditions.In these biological units, bacteria will decomposethe fine organic matter, to produce cleaner
  6. 6. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHThe treatment reactors, in which the organicmatter is decomposed (oxidized) by aerobic bacteria areknown as aerobic biological units; and may consists of(i) Filters (intermittent sand filters as wellas trick long filters).(ii) Aeration tanks with the feed of recycledactivated sludge (i.e., the sludge which Isettled in secondary sedimentation tank,receiving effluents from the aerationtank)(iii) Exudation ponds and Aerated legions.Since the there aerobic units, generallymake use of primary settled sewage,they are early classified as secondaryunits.The effluent from the secondary biologicaltreatment will usually contain a little BOD (5 to 10% of theoriginal). The organic solids sledge separated out in theprimary as wells as in the secondary settling tank will bedisposed of by stabilizing them under anaerobic processin a sludge digestion tank.The final or advanced TreatmentThus treatment is sometimes called tertiarytreatment, and consists in removing the organic local leftafter the secondary treatment, and particularly to kill thepathogence bacteria. Thus treatment, which is normallycarried out by chlorinationShows diagrammatic sketches of some standardtypes of sewage treatment plants2. Describe the types of screens with need sketch.Screening is the very first operation carried out ata sewage treatment plant, so as to trap and remove thefloating matter, such as pieces of cloth, paper, woodcork, hair, fiber, kitchen refuge, fecal solids etc present insewage.Thus, the main idea of providing screens it toprotect the pumps and other equipments from thepossible damages due to the floating matter of thesewage.Types of screens depending upon the size of theopenings and screens may be classified as1) Coarse screen2) Medium screens3) Fine screensCoarse Screen:It is also known as racks and the spacing betweenthe bars (i.e., opening size) is about 50 mm or more.These screens do help in removing large floating objectsfrom sewage. The material separated by coarsescreens, usually consists of rags, wood, paper
  7. 7. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHMedium Screen:The spacing between bars a about 6 to 40 mm.These screens will ordinarily collect 30 to 90 lit ofmaterial per million liter of sewage. The screeningsusually contain some quantity of organic material may bedispersed of by incineration of burial.Rectangular Shaped coarse and medium screensare now – a – days widely used at sewage treatmentplants.Now – a – days these screens are generally keptinclined at about 30 to 60 to the direction of flow, so asto increase the opening area and to reduce the flowvelocity and there making the screening more effective.Fine Screens:Have perforations of 1.5mm to 3mm in size. Theinstallation of there screens prove very effective and theyremove as much as 20% of the suspended solids fromsewage. These screens, however, get clogged veryoften, and need frequent cleaning. They are, therefore,used only for treating the industrial waste waters or fortreating those municipal waste wasters, which areassociated with heavy amounts of industrial wastewaters.These screens will considerably reduce the load onfurther treatment units.Brasses of Bronze plates or wire mesh aregenerally used for constructing fine screens. The metalused to should be resistant to rest and corrosion.Find screens may be disc or drum type, and areoperated continuously by electric motor (Figure S.K.G Figno 277)3. Estimate the screen requirement for a planttreating a peak flow of 60 million liters/day ofsewage.Solution:Peak flow = 60 ML/day6360 10 cu.mday100060,000 m0.694sec24 60 60  Assuming that the velocity through the screen (atpeak flow) is not allowed to exceed 0.8 m/sec we havethe net area of screen openings reg20.6940.87m0.8 
  8. 8. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHUsing Rectangular steel bars in the screen,hawing 1 cm width and placed at 5 m clear spacingThe gross area of the screen required20.87 61.04cm5Assuming that the screen bars are placed at 60 tothe horizontalThe gross area of the screen needed21.04 1.04 21.2m3 32  Hence a coarse screen of 1.2m2area is requiredwhile deigning the screen, we have also to design itscleaning.Frequency:The cleaning frequency is governed by the headloss through the screen. The more the screen openingare clogged, more will be the head loss through thescreen generally not more than half the screen cloggingis allowed to know whether the screen has been cloggedand needs cleaning.The hL through the cleaning screen and halfcleaned screen, can be completed as followsVelocity through the screen = 0.8 m/secVelocity above the screen =0.8 5 msec6= 0.67 m/secHead less through the screen = 0.7929(V2– u2)= 0.7929 (0.82 – 0.672)= 0.0134 ray 0.013 mWhen the screen openings get half clogged then thevelocity through the screenV = 0.8 x 2 = 1.6 m/secHead loss =0.0729(1.62– 0.672)= 0.1538 say 0.15mThis shows that when the screens are totallyclean, the head loss is negligible is about 1.3cm onlywhere as, the hL shoots up to about 15 cm at half theclogging. The screens should therefore be cleanedfrequently as to keep the head loss within the allowablerange.4. A grit chamber is designed to remove particleswith a diameter of 0.2mm, specific gravity 2.65.Settling velocity for there particles has been found
  9. 9. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHrange from 0.016 to 0.22 m/sec, depending on thenshape factor, A flow through velocity of 0.3 m/s. Willbe maintained by proportioning weir determine thechannel dimensions for a maximum waste water flowof 10,000 cum/day.Solution:Let us provide a rectangular channel section,since a proportional flow wear is provided for controllingvelocity of flowNow,Horizontal velocity of flow = Vn = 0.3 m/sSetting velocity is b/w 0.016 to 0.022 m/s and hence let isbe 0.020 m/sNown32Velocity cross sec tion=V A10000 m= 0.116sec24 60 600.116 0.3A0.116A 0.385m0.3     Assuming a depth of 1m, we have the width (B) of thebegin1 B 0.385B 0.385msay0.4m Now settling velocity Vs = 0.02 m/sDetention time = Depth of the burin / settling velocity1 50sec0.02 Length of the tank = Vh x detention tome= 0.3 x 50= 15mHence, use a rectangular tank with dimensionsLength (L) = 15mWidth (B) = 0.4mDepth (b) = 1.0m5. Design a suitable grit chamber cum dexterities fora sewage treatment plant getting a dry weather flowfrom a separate sewerage system @ 400 l/s. Assumethe flow velocity through the tank as 0.2 m/s anddetention period of 2 minutes the maximum flow maybe assumed to be three times of dry weather
  10. 10. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHThe length of the tank= Velocity X Detention time= 0.2 X (2 X 60) = 24 mNow assuming that each detritus tank is designed forpassing D.W.F, we haveThe discharge passing through each tank= 400 l/s = 0.4 m3/ secCross-sectional Area requiredDischargeVelocity0.40.2= 2 m2Assuming the water depth in the tank to be 1.2 m, wehave the width of the tankArea of X sectionDepth21.2= 1.67 mSay 1.7 mHence, use a nitrites tank with 24 m X 1-7 m X 1.2m size At the top, a free-board of 0.3 m may be provided,and at the bottom a dead space depth of 0.45 m forcollection of detritus may be provided.Thus, the overall depth of the tank = 1.2 + 0.3 + 0.45= 1.95 mThe tank will be 1.7 wide up to 1.5 m depth, andthen the sides will slope down to form an elongatedthrough of 24 m length and 0.8 m width at the bottomwith rounded corners, as shown in figure.Detritus tanks:Detritus tanks are nothing but grit chambersdesigned to flow with a smaller flow velocity (of about0.09 m/s) and longer detention periods (about 3 to 4 mini)so as to separate out not only the larger grit etc., but alsoto separate out the very fine sand particles etc.6. Design a grit chamber for a horizontal velocity of25 cm/sec and a flow which ranges from a minimumof 25000 cu-m/day to a maximum of 1,00,000 cu-m/day. Average flow is 62500 cu-m/days. UsingBernoulli’s theoremTotal energy at U/s point in
  11. 11. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECH= Total energy at critical point in controlsection2C1 cVE E 1.59 but E1 = DD = 1.552CV9Using the value of Dmax, as equal to 1.16 at maximumdischarge we haveVc at max1.16X9.81Q1.55= 2.71 m/sAlso yc at Qmax 22C max2.71V at Q0.74mg 9.81  The discharge through the control rection isQ = (W. yc), VCWhere W is the throat width 8 W1 ycis the flow area of the throatW = Q/yc . Vc maxc c maxQWy V bothatQ0.2890.74X2.71= 0.144 m say 0.15 mLet us use throat width 2 = 0.15 mFor other flow conditions:Using the above used two formulas we have2CcVygW . yc . Vc = QVc = Q/w . yc2ccQW.yyg   g. yc . yc2w2=
  12. 12. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECH22c 22c 2Qyg.wQy 3gWKnowing Q and w, we can find yc at different discharges2CVD 1.55gD = 1.55 ycKnowing y, at different discharges, we can find D atdifferent dischargesThen finally we have for a parabolic section2/3 X B X D = A1.5ABDknowing A at various discharges,7. Describe the skimming tanks with neat sketch?Skimming tanks are sometimes employed forremoving oil and greeve from the sewage and placedbefore the sedimentation tanks. They are, therefore usedwhere sewage contains too much of grease or oils whichinclude fats, wakes, soaps, fatty acids.If such greasy and oily matter is not removed fromthe sewage before if enters further treatment units, it mayform unsightly and odourous scums on the surface of thesettling tanks or interfere with the activated sludgetreatment process.These oil and greasy materials may be removed ina skimming tank, in which air is blown by an aeratingdevice through the bottom the rising air tens to coagulateand longeal. (solidify) the grease and cause it to rise tothe surface (being pushed in separate compartments)from where it is removed.The typical details of a skimming tank as
  13. 13. VEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHVEL TECH VEL MULTIMEDIA VEL HIGHTECH VEL TECH VEL MULTIMEDIA VEL HIGHTECHIt consists of a long trough shaped structuresdivided into two or three lateral compartments by meansof vertical baffle walls (having slots in them) for a shortdistance below the sewage surface as shown. The bafflewalls help in pushing the rising coagulated greasymaterial into side compartments (called stillingcompartments) the rise of oils and grease is broughtabove by blowing compressed air into the sewage fromdiffusers placed at the bottom of the tank.The collected greasy materials are removed (i.e.skimmed off) either by hand or by some mechanicalequipment. It may then be disposed of either by burningor burial.A detention period of about 3 to 5 min is usuallysufficient, and t he amount of compressed air required isabout 300 to 6000 m3per million lit of sewate.Surface Area = 0.00622r9Vg  Rate of flow of sewage in m3/dayVr  Minimum rising velocity of greasymaterial to be removed in m/min- 0.25 m/minute in most cases.The efficiency of a skimming tank can beincreased considerably (3 to 4 times) by pausing chlorinegas /2 mg / lit of sewage) along with the compressed