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Do sag curve

DABTU Wastewater Treatment T E (CIVIL)

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Do sag curve

  1. 1. Common Instructions • In order to avoid flooding of emails and speed up assessment from this week Assignments will be submitted in following manner 1. Make group of 5 students roll no. wise e.g. 1 to 5, 6 to 10, 11 to 15 and so on…..66 to 72 or 73 can be a last group 2. Roll no.s 1, 6, 11, 16 ….. Will collect assignments of their group members. (Every student submit his/her assignment to group coordinator clearly naming his file as per Class roll no. and assignment no. e.g. Div.roll no. assignment no. → A01Asg4 B01Asg4) 3. Group coordinators to report defaulter students. Happy Learning ! 2
  2. 2. Online Lecture - 7 Self Purification of Streams and DO Sag Curve Wastewater Treatments Module-II 3
  3. 3. Can you identify the river (from India)? 4
  4. 4. Water Pollution
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  8. 8. What is self purification of stream? • When wastewater is discharged into the river or stream, the BOD of mix increases initially and DO level starts falling. • As river water travels further BOD gradually reduces and DO increases and reaches its saturation level. • Thus river gets purified on its own. • This phenomena is known as self purification of stream 9
  9. 9. Disposal by dilution • Disposal by dilution is a process in which the treated wastewater from ETPs is discharged in a large static body of water or in moving water bodies such as rivers or streams. • The discharged wastewater is purified in due course of time, by the self purification process of natural waters. • The effluent discharge and degree of treatment of wastewater depends upon the self purification capacity of the river and its intended water use 10
  10. 10. Conditions favouring dilution without treatment 1. Where wastewater is quite fresh. 2. SS have been removed from wastewater 3. Volume of receiving water body is more than the wastewater discharge 4. Dilution water having high DO, to satisfy the BOD of wastewater 5. Where swift forward currents are available 6. Wastewater does not contain toxic substances 7. Water is not used for drinking immediately after point of discharge. 11
  11. 11. Standards of dilution Dilution factor Standards of purification required Above 500 No treatment required. Raw sewage can be directly discharged into river Between 300 to 500 Primary treatment such as PST is required so that SS concentration is less than 150 mg/lit Between 150 to 300 Treatment such as screening, sedimentation and chemical precipitation are required so that SS concentration is less than 50 mg/lit Less than 150 Thorough treatment is required SS should be less than 50 mg/lit and BOD 5 should be less than 20 mg/lit 12
  12. 12. ACTIONS INVOLVED IN SELF PURIFICATION OF STREAMS 13
  13. 13. 1. Dilution • When sewage is discharged into a large volume of water flowing in a natural stream or river, it is dispersed and dilution takes place. • Due to dilution the concentration of various constituents such as organic matter, BOD, suspend solids, etc., is reduced and thus the potential nuisance of sewage is also reduced. • Analogy for dilution is Making of Rasana or juice from any squash 14
  14. 14. 15
  15. 15. Qw, BODw, DOw Qr, BODr, DOr 1.Dilution :- 2. Combined BOD and DO determination for a stream Residents Qmix, BODmix, DOmix • Combined waste flow Qmix = Qr + Qw • Combined BOD Qr.BODr + Qw.BODw Qr + Qw BODmix = • Combined DO Qr.DOr + Qw.DOw Qr + Qw DOmix =
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  17. 17. Problem Using following data find out properties of resultant mix River Wastewater Flow (m3 /sec) 0.7 0.231 DO (mg/lit) 8.2 2 BOD5 (mg/lit) 3.4 45 Temperature (o C) 23 26 State whether you can find out pH of mix by using the formula that you have used to find DO, BOD and Temperature of mix? If answer is no, Why? 18
  18. 18. 19
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  20. 20. • No. pH can not be determined by above equation. • pH varies logarithmically therefore pH of mix can be found out by different formula. 21
  21. 21. Assignment 4 • Problem 1. 22 River Sewage Flow (m3/sec) 8 1.25 BOD5 2 250 DO 8 0 Temp 0C 15 20 Determine Properties of mix for above parameters
  22. 22. Online Lecture - 8 Self Purification of Streams and DO Sag Curve Wastewater Treatments Module-II 23
  23. 23. 2. Dispersion due to currents • Self purification largely depends upon currents, which readily disperses wastewater in the stream, preventing locally high concentration of pollutants. • High velocity improves aeration which reduces the concentration of pollutants. • High velocity improves re-aeration which reduces the time of recovery, though length of stream affected by the wastewater is increased. 24
  24. 24. 3. Sedimentation • If stream velocity is lesser than the scour velocity of particles then sedimentation will take place, which has two effects 1. SS contribute largely to BOD will be removed by settling and hence downstream water quality will be improved. 2. Due to settled solids anaerobic decomposition may take place 25
  25. 25. 4. Oxidation • The organic matter present in the wastewater is oxidized by aerobic bacteria utilizing dissolved oxygen of the natural waters. • This process continues till complete oxidation of organic matter takes place. • The stream which can absorb more oxygen through reaeration can purify heavily polluted water in short time 26
  26. 26. 5. reduction • Reduction occurs in the stream due to hydrolysis (separation of water from organic molecules) of organic matter biologically or chemically. • Anaerobic bacteria will split the organic matter into liquids and gases, thus paving the way for stabilization by oxidation 27
  27. 27. 6. temperature • At low temp activity of bacteria is low., and hence decomposition is slow., though DO will be more because increased solubility of oxygen in water. • At higher temperature purification will take lesser time though amount of DO is less in the water. 28
  28. 28. 7. Sunlight • Sunlight helps certain micro-organisms to absorb CO2 and give out oxygen, thus resulting in self purification. • Sunlight acts as disinfectant and stimulates growth of algae which produces oxygen during photosynthesis. • Hence wherever there is algal growth water contains more DO during daytime. 29
  29. 29. ZONES OF POLLUTION IN THE STREAM 30
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  31. 31. 1. Zone of degradation • Situated just below outfall sewer • Water is dark and turbid with sludge at the bottom • DO reduces up to 40% of saturation level • CO2 content increases • Rearation is slower than deoxygenation • Conditions are unfavorable for aquatic life • Anaerobic decomposition takes place in this zone 32
  32. 32. 2. Zone of active decomposition • Water in this zone becomes greyish and darker than previous zone • DO concentration falls to zero • CH4, H2S, CO2 and N2 are present because of anaerobic decomposition • Fish life is absent but bacteria are present • At the end of this zone DO rises to 40% of saturation • Aquatic life starts to reappear. 33
  33. 33. 3. Zone of recovery • Process of recovery starts • Stabilization of organic matter takes place in this zone • BOD falls and DO content increases above 40% value • NO4, SO4 and CO3 are formed. • Near the end of this zone entire aquatic life reappears 34
  34. 34. 4. Clear water zone • Water becomes clearer and attractive in appearance • DO rises to saturation level • Oxygen balance is attained • Recovery is complete • Some pathogenic microorganisms may be present 35
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  38. 38. Online Lecture - 9 Self Purification of Streams and DO Sag Curve Wastewater Treatments Module-II 39
  39. 39. DO SAG CURVE 40
  40. 40. Deoxygenation and Reoxygenation curves 41
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  42. 42. • When pollutional load is discharged into the stream, DO goes on reducing. This process is known as deoxygenation. • It depends upon organic matter present and temperature. • The variation or depletion of DO is represented graphically by deoxygenation curve. 43
  43. 43. • At the same time oxygen gets added into the stream through various processes such as photosynthesis, rains etc. • The curve representing oxygen gaining process is known as Reoxygenation or reaeration curve • In a running polluted stream deoxygenation and reaeration processes go hand in hand. • Id deoxygenation is more deficit results. 44
  44. 44. • The amount of DO deficit can be obtained by graphically adding both the curves. The resultant curve is known as ‘DO sag curve’. • DO deficit is given by DO deeficit = saturation DO – Actual DO = DO sat - DO act • Streeter Phelps equation can be used for analysis of DO sag curve 45
  45. 45. Streeter Phelps Equation 46
  46. 46. Streeter Phelps Equation 47
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  48. 48. 49
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  50. 50. • Xc = Critical distance = V x tc V = Velocity of flow 51
  51. 51. Quiz • Today at 5 pm • MCQ and one numerical on finding properties of mix 52
  52. 52. Objective questions 1. When Wastewater is discharged into the river ________reduces and _______increases suddenly. 2. Most polluted zone in self purification process is zone of __________. 3. Initial DO deficit is given by _________ minus _________. 4. ________equation is used for modelling of self purification of streams process. 5. The at which DO deficit reaches its min value is called as _____ ______. 53
  53. 53. 6. Critical distance is given by _______. 7. Max. value of DO saturation at 20o C for water is _____mg/lit. 8. At Lower temperature activity of microorganisms is ____ but DO present in water is _____. 9. At higher temperature activity of microorganisms is ____ but DO present in water is _____. 10. When pollutional load is discharged into the stream, DO goes on reducing. This process is known as ___________. 54
  54. 54. 11.The curve representing oxygen gaining process is known as ___________or _________ curve. 12. If stream velocity is lesser than the scour velocity of particles then __________ will take place. 13. Self purification largely depends upon _______, which readily disperses wastewater in the stream, preventing locally high concentration of pollutants. 55
  55. 55. Theory questions Q1. Explain self purification of stream process. Q3. Write short notes on 1. Actions involved in self purification of stream. 2. Zones of pollution in the stream. 3. Streeter Phelps equation 4. DO sag curve 56

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  • SubhashPatil37

    Nov. 3, 2020

DABTU Wastewater Treatment T E (CIVIL)

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