L 17 do sag [compatibility mode]
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This document discusses various aspects of self-purification of streams, including: 1. Water pollution can come from point sources like factories or sewage systems, which are easier to identify and control, or non-point sources like agricultural runoff, which are harder to control. 2. Self-purification occurs through dilution, dispersion, sedimentation, oxidation, reduction, and effects of temperature and sunlight. Bacteria break down organic pollutants, using up dissolved oxygen. 3. A DO sag curve shows how dissolved oxygen levels decrease from the input point due to biochemical oxygen demand, before eventually reaching a critical point and recovering further downstream.
L 17 do sag [compatibility mode]
- 1. L-17 Self Purification of Streams and DO Sag CurveDO Sag Curve Industrial Waste Treatment 1
- 2. Can you identify the river (from India)? 2
- 4. Causes of Water Pollution Factors that contribute to water pollution can be categorized into two different groups Point sources Non-point sources Point sources are the easiest to identify and control Non point sources are ambiguously defined and harder to control
- 5. Point Sources Some point sources of water pollution include Waste products from factories Waste from sewage system Waste from power plantsWaste from power plants Waste from underground coalmines Waste from oil wells They are called point sources because they are direct sources of water pollution and can be reduced and monitored
- 6. Example of a point source
- 7. Non-point Sources The term non-point source comprises of large range of sources such as: when rain or snow moves through the ground and picks up pollutants as it moves towards a major body of waterbody of water the runoff of fertilizers from farm animals and crop land air pollutants getting washed or deposited to earth storm water drainage from lawns, parking lots, and streets
- 8. Non-point source: Agricultural runoff
- 9. Point and Non-point Source Pollutions
- 10. Organic Pollution and Oxygen Demand Bacteria C6H12O6 +6O2 6CO2 + 6H2O 180 g 192 g 1g glucose = 192/180g O2 1g glucose consumes 1.07g O21g glucose consumes 1.07g O2 1g glucose has BOD of 1.07g Organic matter in waste + O2 in stream CO2 + H2O DO level ≤ 2.0 mg/L, some fish and other aquatic animal Species may be distressed and some species may even die due to suffocation. As a rule of thumb DO level of 4 mg/L should be maintained
- 11. Organic Pollution and Fish Kill
- 12. 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 dueThe 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 12
- 13. 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 Dilution water having high DO, to satisfy the4. 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. 13
- 14. 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/litthan 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 14
- 15. ACTIONS INVOLVED IN SELF PURIFICATION OF STREAMS 15
- 16. Qw, BODw, DOw Qr, BODr, DOr 1.Dilution :- 2. Combined BOD and DO determination for a stream Residents • Combined waste flow Qmix = Qr + Qw • Combined BOD Qmix, BODmix, DOmixQrBODr + QwBODw Q1 + Q2 BODmix = • Combined DO Qr.DOr + Qw.DOw Q1 + Q2 DOmix =
- 17. 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 whichHigh velocity improves aeration which reduces the concentration of pollutants. High velocity improves raeration which reduces the time of recovery, though length of stream affected by the wastewater is increased. 17
- 18. 3. Sedimentation If stream velocity is lesser than the scour velocity of particles then sedimentation will takes place, which has two effects 1. SS contribute largely to BOD will be removed by settling and henceremoved by settling and hence downstream water quality will be improved. 2. Due to settled solids anaerobic decomposition may take place 18
- 19. 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.organic matter takes place. The stream which is capable of absorbing more oxygen through reaeration etc can purify heavily polluted water in short time 19
- 20. 5. reduction Reduction occurs in the stream due to hydrolysis of organic matter biologically or chemically. Anaerobic bacteria will split the organic matter into liquids and gases, thus pavingmatter into liquids and gases, thus paving the way for stabilization by oxidation 20
- 21. 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 willAt higher temperature purification will take lesser time though amount of DO is less in the water. 21
- 22. 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 producesstimulates growth of algae which produces oxygen during photosynthesis. Hence wherever there is algal growth water contains more DO during daytime. 22
- 23. ZONES OF POLLUTION IN THE STREAM 23
- 24. 24
- 26. DO SAG CURVE 26
- 27. DO Sag Curve Residents Q1, BOD1 SS1 Industry Q2, BOD2 SS2 Dissolvedoxygen,mg/L Saturation DO (Cs) Travel time, days Initial deficit D0 Oxygen addition (reaertaion) Oxygen depletion Critical deficit (Dc) tc
- 28. Self purification of streams:Contributors 28
- 29. InitialInitial Deficit (DDeficit (Daa)) Saturation DO (DoSaturation DO (Doss)) DeficitDeficit CriticalCritical 1010 88 66 44 DissolvedOxygen(mg/L)DissolvedOxygen(mg/L) Typical DO sag curve 29 DO Concentration (DO)DO Concentration (DO) CriticalCritical PointPoint ttcc 2 4 6 8 102 4 6 8 10 Travel Time (d)Travel Time (d) 44 22 DissolvedOxygen(mg/L)DissolvedOxygen(mg/L)
- 30. Theory questions Q1. Explain self purification of stream process. Q2. Discuss- What are point and non point sources? Q3. Write short notes on Actions involved in self purification of stream.1. Actions involved in self purification of stream. 2. Zones of pollution in the stream. 3. Streeter Phelps equation 4. DO sag curve 30