Wastewater engineering info

Introduction: Wastewater flow and its characteristics, Wastewater collection systems, Estimation and variation of wastewater flows. Problems of industrial wastewaters, sampling protocol, equalization, neutralization, proportioning processes, volume and strength reduction. Preliminary, primary, secondary and tertiary wastewater treatment processes. Theory
and design of screens, grit chambers, sedimentation, coagulation, flocculation

1. DEPARTMENT OF CHEMICALENGINEERING
CHAPTER-1
“Introduction of Wastewater”
PROF. DEVARSHI P. TADVI
ASSISTANT PROFESSOR
CHEMICAL ENGINEERING
DEPARTMENT
S S AGRAWAL INSTITUTE
OF
ENGINEERING & TECHNOLOGY,
NAVSARI
WASTEWATER ENGINEERING

2. OUTLINE
•Introduction
•Objectivesofwatertreatment
•Conventional water treatment plantlayout
•Various Methods of purification ofwater
•Screening
•PlainSedimentation
•Sedimentation aided withcoagulation
•Filtration
•Disinfection
•Aeration
•Softening

3. What isWastewater?
•Wastewaterisatermthatisusedtodescribewastematerial
thatincludesindustrialliquidwasteandsewagewastethatis
collectedintownsandurbanareasandtreatedaturban
wastewatertreatmentplants.

4. Wheredoes wastewater come from?
•Residences
― human and animal excreta and waters used for washing, bathing, andcooking.
•Commercial institution
•Dairy and industrial establishment
― slaughterhouse waste, dairy waste, tannery wastewater,etc.

5. Where does it allgo!
Where doesthe
water from the
washergo?
When you flushthe
toilet where does the
contentsgo?
By gravity flow, the waste is on its way to your
local wastewater treatmentplant!

6. Wastewatertreatment
•Aprocesstoconvertwastewater-whichiswaternolongerneededor
suitableforitsmostrecentuse-intoaneffluentthatcanbeeither
returnedtothewatercyclewithminimalenvironmentalissuesorreused.
•Watertreatmentistheprocessofmakingwatersuitableoracceptablefor
anend-use.
•Itremovesexistingwatercontaminatsandso,reducetheirconcentration
thatthewaterbecomesfitforit’sdesiredapplication.
•Theamount&typeoftretmentprocess(TreatmentTrain)dependsupon
qualityofRawWaterandvariousstandardsRequiredaftertreatment.

7. WastewaterContaminants
•Suspendedsolids
•Biodegradable organics (e.g.,BOD)
•Pathogenicbacteria
•Nutrients (N &P)

8. Objectivesofwatertreatment
•The objectives of water treatment are toproduce:
•Water that is safe for humanconsumption
•Water that is appealing aesthetically to theconsumer
•Water at a reasonable cost

9. Indian Standards for drinkingwater

10. Screening
Coagulation
Flocculation
Sedimentation
Filtration
Disinfection
Storage
Distribution
Rawwater
Alum
Cl
2
sludge
sludge
sludge
7

11. Functions of Water TreatmentUnits

12. Selection of treatmentprocess-Train
Thetypesoftreatmentrequiredfordifferentsourcesaregiveninthe
followingtable:

13. WHY TREATWASTEWATER ?
•Causes a demand for dissolved oxygen (lower DO
levels ofstreams)
•Adds nutrients (nitrate and phosphate) to cause
excessivegrowth
•Increases suspended solids or sediments in
streams (turbidityincrease)

14. •Reduce organic content i.e.,BOD
•Removal/reduction of nutrients i.e.,N,P
•Removal/inactivation of pathogenic
microbes
OBJECTIVES OFWWT

15. LEVELS OFTREATMENT
•Primary
–removal by physical separation of grit and large objects (material to
landfill for disposal)
–Sedimentation and screening of largedebris
Secondary
–Biological and chemicaltreatment
–aerobic microbiological process(sludge)
organic matter + O
2 CO
2+NH
3+H
2O
NH
3 NO
3
-
aquaticnutrient
Mostlydead
microbes

17. Treatment stages -Primary treatment
•typical materials that are removed
during primary treatmentinclude
–fats, oils, andgreases
–sand, gravels androcks
–larger settle-able solids including human
waste, and
–floating materials

18. Methods used inprimary treatment
•Bar screens
•Grinding
•GritChamber
•SedimentationTank-primarySettling tank
•Chlorination ofeffluent

20. Sedimentation Tank-Primary Settlingtank
–Remove grease, oil
–Fecal solid settle, floating material rise to the surface
–Produce a homologous liquid for later biological
treatment
–Fecal sludge are pumped to sludge treatmentplant

21. Secondarytreatment
•Biologicaltreatment
–activatedsludge
–tricklingfilter
–oxidationponds

22. Activated sludgeprocess
•Primary wastewater mixed with bacteria-rich (activated)
sludge and air or oxygen is pumped into the mixture
•Both aerobic and anaerobic bacteria mayexist
•Promotes bacterial growth and decomposition of
organicmatter
•BOD removal is approximately85%
•Microbial removal by activatedsludge
•80-99% removal ofbacteria
•90-99% removal ofviruses

23. 5 physicalcomponents
•Aerationtank
•oxygen is introduced into thesystem
•Aerationsource
•ensure that adequate oxygen is fed into thetank
•provided pure oxygen or compressedair
•Secondaryclarifiers
•activated-sludge solids separate from the surrounding
wastewater
•Activated sludge outflowline
•Pump activated sludge back to the aerationtank
•Effluent outflowline
•discharged effluent into bay or tertiary treatmentplant

25. Aeration
andrapid
mixing
Settling collects
sludge on
bottom
Secondaryprocess
iriffuser
From primary
process
To
tertiary
proc
ess

26. •Trickling filters are beds made of coke (carbonized coal),
limestone chips or specially fabricated plasticmedia
•Optimize their thickness by insect or wormgrazing
•The primary wastewater is sprayed over the filter and microbes
decompose organic materialaerobically.
•Low pathogenremoval
-Bacteria,20-90%
-Viruses,50-90%
-Giardia cysts,70-90%
Tricklingfilters

28. Stabilization oroxidation
PONDS
•
•
•
•
•
Oxidation ponds are a few meters deep, and up to a hectare
insize.
They are low cost with retention times of 1 to 4 weeks. Odor
and mosquitoes can be aproblem
Pathogen removal:
-Bacteria,90-99%
-Virus,90-99%
-Protozoa,67-99%
Mechanisms include the long detention time, high pH (10-10.5)
generated by photosynthesis, predation, sunlight, temperature

29. Continued…
Stabilization ponds are the preferred
wastewater treatment process in developing
countries due to low cost, lowmaintenance.
This is balanced by larger landrequirement.

30. When the treatment isdone…
•Effluent back to streamafter
–a final carbon filtrationand
–chlorination/de-chlorination
•Sludge –very nutrientrich
–applied directly to land asfertilizer
–incinerated (good fuel afterdrying)
–composted

31. Sludge TreatmentProcesses
Thickening(waterremoval)
Digestion (pathogen inactivation and odorcontrol)
Conditioning (improved dewateringwith
alum and high temp, 175-230
oC)
Dewatering (pathogen inactivation and odorcontrol)
Incineration (volume and weightreduction)
Final disposal

32. •SepticTanks
•
•Constructed
Wetlands
Composting
Wastewater
Treatment
Alternatives

33. Removeslargesolidslogs
branchesragsfish
Simpleprocess
mayincorporateamechanizedtrashremovalsystem
ProtectspumpsandpipesinWaterTreatmentPlants

34. PlainSedimentation
Sedimentation is the removal of suspendedparticles
by gravitationalsettling.
TypesofSedimentationTanks
1)FillAndDrawType
2)Continuous Flowtype

35. Shape of sedimentationtank
1.Rectangular
tank with
horizontalflow.
2.Circulartank
withradialor
spiralflow.
3.Hopperbottom
tank with
verticalflow.

36. SEDIMENTATION
Waterflowstoatankcalleda
sedimentationbasin
Gravitycausestheflocstosettle
tothebottom
Itwouldtakeaverylongtimefor
allparticlestosettleoutandthat
wouldmeanwewouldneeda
verylargesedimentationbasin.

37. Sedimentationaidedwith coagulation
Sedimentationaddedwithcomprisesofthreestep
Additionofmeasuredquantityofchemicalscalled
coagulantstowaterandtheirthroughmixing(rapid
mixing).
Formationofprecipitatewhichcoagulatesandformsa
flow(flocculation)
Sedimentation

38. Coagulants
Aluminum Sulfate
Al2(SO4)3
Ferrous SulfateFeSO4
Ferric SulfateFe2(SO4)3
Ferric Chloride FeCl3
LimeCa(OH)2
Aluminumsaltsarecheaper
butironsaltsaremore
effectiveoverwiderpHrange
15

39. AerationUnit
Work : Diffusion ofAir
Removes odour andtastes
Oxidizesironandmanganese,increasesdissolvedoxygencontentin
water,removesCO2andreducescorrosionandremovesmethaneand
otherflammablegases.
Types ofAerators
1.Gravityaerators
2.Fountainaerators
3.Diffusedaerators
4.Mechanicalaerators.

40. GravityAerators(Cascades):Ingravityaerators,
waterisallowedtofallbygravitysuchthatalargearea
ofwaterisexposedtoatmosphere,sometimesaidedby
turbulence.
AerationUnit

41. Injection or Diffused Aerators :It
consistsofatankwithperforated
pipes,tubesordiffuserplates,fixed
atthebottomtoreleasefineair
bubblesfromcompressorunit.Time
ofaerationis10to30minand0.2to
0.4litresofairisrequiredfor1litre
ofwater.
AerationUnit

42. FountainAerators:Thesearealsoknownasspray
aeratorswithspecialnozzlestoproduceafinespray.Each
nozzleis2.5to4cmdiameterdischargingabout18to36
l/h.Nozzlespacingshouldbesuchthateachm3ofwater
hasaeratorareaof0.03to0.09m2foronehour.
AerationUnit

43. MechanicalAerators
flocculationareused.
:Mixing
Paddles
paddles
maybe
asin
either
submerged or at thesurface.
AerationUnit

44. Types of MixingDevices
Mixings basins with bafflewalls

45. Mixing Basins Equipped with Mechanicaldevicies

46. Flocculation
Flocculationisaslowmixingoragitatingprocessinwhich
thedestablishedcolloidalparticlesarebroughtinto
intimatecontactinordertopromotetheflocformation.
Rate of flocculation dependsupon
Types and amount ofturbidity
Types ofcoagulant
Dosages ofcoagulant
Mean velocity gradient inbasin

47. Clariflocculator
Clarifierandflocculatorareprovidedinsingleunit
calledclariflocculator.
Theflocculatingchamberisprovidedinthecentre
andclarifiercomponentisformedbytheperipheral
space.
Velocity of flowof water around 0.3 m/min.
Mechanical scrapper provided to removesludge.

49. Filtration
The process of passing the water through the beds of
such granular material is known asfilteraton
Types ofFiltration
Slow sand gravityfilter
Rapid sand gravityfilter
1.Rapid sand gravityfilter
2.Pressurefilter

52. Method ofdisinfection
Physicalmethod
Byheat
By U.V.rays
Chemicalmethod
Oxidizingchemicals
Metalions
Alkalis andacids
Minormethod
Boiling ofwater
Treatment with excesslime
Treatment withozone
Treatment with iodine and bromine
Treatment with ultra-violet rays
Treatment with potassiumpermanganate

53. Watersoftening
Waterissaidtobehardwhenitcontainsrelativelylarge
amountsofbicarbonates,carbonates,sulphatesand
chloridesofcalciumandmagnesiumdissolvedinit.
Types ofHardness
Temporaryhardness
Permanenthardness

54. Types ofHardness
causedbydissolvedTemporaryHardness-
bicarbonatesofCaandMg.
-AKA ‘alkaline or carbonatehardness’
PermanentHardness–causedbydissolved
chloridesandsulphatesof Ca, Mg, Fe and Aletc.

55. RemovalofHardness
Removal of temporaryhardness
1.Boiling
2.By addinglime
Removal of temporaryhardness
1.Lime-sodaprocess
2.Zeoliteprocess
3.Demineralization or De-ionizationprocess

56. Disinfection
Thefilteredwatermay
normallycontainsome
harmfuldiseaseproducing
bacteriainit.
Thesebacteriamustbe
killedinordertomakethe
watersafefordrinking.
The process of killingthese
Disinfection
bacteriaisknownas
or
Sterilization.

57. Methods ofDisinfection
Boiling: The bacteria present in water can be destroyed by boiling it for along
time. However it isnot.
TreatmentwithExcessLime:Limeisusedinwatertreatmentplantfor
softening.Butifexcesslimeisaddedtothewater,itcaninaddition,killthe
bacteriaalso.Treatmentlikerecarbonationforlimeremovalshouldbeused
afterdisinfection.
TreatmentwithOzone:Ozonereadilybreaksdownintonormaloxygen,and
releasesnascentoxygen.Thenascentoxygenisapowerfuloxidizingagentand
removestheorganicmatteraswellasthebacteriafromthewater.
Chlorination:Thegermicidalactionofchlorineisexplainedbytherecent
theoryofEnzymatichypothesis,accordingtowhichthechlorineentersthecell
wallsofbacteriaandkilltheenzymeswhichareessentialforthemetabolic
processesoflivingorganisms.

58. Reference
•Mahajan PublishingHouse
http://web.iitd.ac.in/~arunku/files/CVL100/L8.pdf
http://nptel.ac.in/courses/105104102/Lecture%2020.ht m
http://www.sswm.info/sites/default/files/reference_at
tachments/SCHUTTE%202007%20Handbook%20for
•%20the%20Operation%20of%20Water%20Treatment
•%20Works.pdf
-4
th
Water&wastewaterEngineering editionBy

59. Thank You