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Module iii

DABTU Wastewater Treatment T E (CIVIL)

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Module iii

  1. 1. Online Lecture - 12 Industrial Wastewater Treatment and management Wastewater Treatments Module-III 1
  2. 2. Introduction
  3. 3. Contaminants Reason for Importance Suspended solids Suspended solids can lead to the development of sludge deposits and anaerobic conditions when untreated wastewater is discharged in the aquatic environment. Nutrients Both nitrogen and phosphate, along with carbon, are essential nutrients for growth. When discharged to the aquatic environment, these nutrients can lead to the growth of undesirable aquatic life. When discharged in excessive amounts on land, they can also lead to the pollution of groundwater. Priority pollutants Organic and inorganic compounds selected on the basis of their known or suspected carcinogenicity, or high acute toxicity. Refractory organics These organics tend to resist conventional methods of wastewater treatment. Typical examples include surfactants, phenols, and agricultural pesticides. Heavy metals Heavy metals are usually discharged to wastewater from commercial and industrial activities and have to be removed if the wastewater is to be reused. Dissolved inorganics Inorganic constituents such as calcium, sodium, and sulphate are added to the original domestic water supply as a result of water use and may have to be removed if the wastewater is to be reused.
  4. 4. Characteristics of industrial waste and effect on receiving waters • 1. Soluble organics causing depletion of dissolved oxygen—Since most receiving waters require maintenance of minimum dissolved oxygen, the quantity of soluble organics is correspondingly restricted to the capacity of the receiving waters for assimilation or by specified . • 2. Suspended solids—Deposition of solids in quiescent stretches of a stream will impair the normal aquatic life of the stream. Sludge blankets containing organic solids will undergo progressive decomposition resulting in oxygen depletion and the production of noxious gases.
  5. 5. • 3. Priority pollutants such as phenol and other organics dis- charged in industrial wastes will cause tastes and odours in the water and in some cases are carcinogenic. If these contaminants are not removed before discharge, additional water treatment will be required. • 4. Heavy metals, cyanide, and toxic organics— • 5. Colour and turbidity— These present aesthetic problems even though they may not be particularly deleterious for most water uses. In some industries, such as pulp and paper, colour removal can be difficult and expensive.
  6. 6. • 6. Nitrogen and phosphorus— When effluents are discharged to lakes, ponds, and other recreational areas, the presence of nitrogen and phosphorus is particularly undesirable.Excessive accumulation in water bodies causes ‘Eutrophication’. • 7. Oil and Grease – If not removed from industrial wastewater it creates a layer on surface of water bodies thus affecting oxygen transfer for photosynthesis. Also causes aesthetical problems.
  7. 7. Difference between Sewage and Industrial Wastewater Sewage Industrial wastewater Domestic wastewater is wastewater originating from activities such as restroom usage, washing, bathing, food preparation, and laundry. Industrial wastewater is process wastewater originating from manufacturing, commercial businesses, mining, agricultural production and processing, and wastewater from clean- up of petroleum and chemical contaminated sites, to name a few. Characteristics are constant. Not much variation. Characteristics may change. Depends upon processes adopted. Does not contain heavy metals May contain heavy metals such as Pb. Hg. Cr6+
  8. 8. Sludge generated in WTP can be reused in Farm fields Sludge can be hazardous in nature. Cant be used in farm fields. Tertiary treatment is optional. Tertiary treatment is needed for recycling of wastewater Fixed flow pattern No fixed flow pattern Low pollution strength Higher pollution strength
  9. 9. Polluting Industries Industry Wastes Produced Type of Pollution 1. Caustic Soda Mercury, Chlorine gas Air, water and land 2. Cement dust, smoke Particulate matter – 3. Distillery Organic waste Land and water 4. Fertiliser Ammonia, cyanide, oxides of nitrogen, Air and water oxides of sulphur 5. Dye Inorganic waste pigment Land and water 6. Iron and steel Smoke, gases, coal dust, fly ash, fluorine Air, water and land
  10. 10. 7. Pesticides Organic and inorganic Water and land waste 8. Oil Refineries Smoke, toxic gases, organic waste Air and water 9. Paper and Pulp Smoke, organic waste Air and water 10. Sugar Organic waste, molasses Land and water 11. Textiles Smoke, particulate matter Land and water 12. Tanneries Organic waste Water
  11. 11. 13. Thermal power Fly ash, SO2 gas Air and water 14. Nuclear power station Radioactive wastes Water and land 15. Food processing Alkalies, phenols chromates, organic wastes Water and land
  12. 12. Pollution Prevention • Pollution prevention (P2) is any practice that reduces, eliminates, or prevents pollution at its source, also known as "source reduction." • Source reduction is fundamentally different and more desirable than recycling, treatment and disposal. • There are significant opportunities for industry to reduce or prevent pollution at the source through cost-effective changes in production, operation, and raw materials use. • The opportunities for source reduction are often not realized because existing regulations focus upon treatment and disposal.
  13. 13. • Pollution prevention approaches include: • increasing efficiency in energy use; • use of environmentally friendly fuel sources.
  14. 14. • In the industrial sector, examples of P2 practices include: 1. Modifying a production process to produce less waste 2. Using non-toxic or less toxic chemicals as cleaners, degreasers and other maintenance chemicals 3. Implementing water and energy conservation practices 4. Reusing materials such as drums and pallets rather than disposing of them as waste
  15. 15. • Control of Industrial Pollution: • Some important control measures are: 1. Control at Source: It involves suitable alterations in the choice of raw materials and process in treatment of exhaust gases before finally discharged and increasing stock height up to min. 30 metres in order to ensure proper mixing of the discharged pollutants. 2. Selection of Industry Site: The industrial site should be properly examined considering the climatic and topographical characteristics before setting of the industry.
  16. 16. 3. Treatment of Industrial Waste: The industrial wastes should be subjected to proper treatment before their discharge. 4. Plantation: Intensive plantation in the region, considerably reduces the dust, smoke and other pollutants. 5. Stringent Government Action: Government should take stringent action against industries which discharge higher amount of pollutants into the environment than the level prescribed by Pollution Control Board.
  17. 17. 6. Assessment of the Environmental Impacts: Environmental impact assessment should be carried out regularly which intends to identify and evaluate the potential and harmful impacts of the industries on natural eco-system. 7. Strict Implementation of Environmental Protection Act: Environment Protection Act should be strictly followed and the destroyer of the environment should be strictly punished.
  18. 18. • Use good housekeeping practices. Sweep, vacuum and mop floors rather than hosing them down, and don’t leave sweepings outside where rain can wash them into storm drains. Clean up spills immediately. Sweep parking lots, before the rains come. Be aware that rubber from tires and other products from automobiles contribute to water pollution. • Store chemicals and liquids sensibly. Store chemicals so they can be found and identified easily.
  19. 19. • Spill prevention and control. • Use chemicals only in designated areas where spills can be contained. Avoid moving chemicals long distances from storage to use. Properly dispose of rags and absorbents. • Train employees- All employees—whether or not they work with chemicals—should receive training about the products in use, storage requirements, spill procedures and potential hazards. • Reduce chemical use whenever possible.
  20. 20. Online Lecture - 13 Industrial Wastewater Treatment and management Wastewater Treatments Module-III 28
  21. 21. Equalization • Equalization is a method of retaining waste in a basin so that the effluent discharged is fairly uniform in its water quality characteristics (pH, colour, turbidity, alkalinity, biochemical oxygen demand [BOD], and so forth). • A secondary but significant effect is that of lowering the concentration of effluent contaminants. • This is accomplished not only by ironing out the slugs of a high concentration of contaminants but also by physical, chemical, and biological reactions that may occur during retention in equalization basins.
  22. 22. Before Equalization
  23. 23. Objectives of Equalization • Equalization improves sedimentation efficiency by improving hydraulic retention time • The efficiency of biological process can be increased because of uniform characteristics and minimization of the impact of shock loads and toxins during operation • Manual and the automated control of flow- rate-dependent operations, such as chemical feeding, disinfection, and sludge pumping are simplified.
  24. 24. • Treatability of the waste water is improved and some BOD reduction and odour removals provided if aeration is used for mixing in the equalization basin • A point of return for recycling concentrated waste stream is provided, thereby mitigating shock loads to primary setters or aeration basin
  25. 25. • Air is sometimes injected into these basins to provide: (1) better mixing; (2) chemical oxidation of reduced compounds; (3) some degree of biological oxidation; and (4) agitation to prevent suspended solids from settling. • The size and shape of the basins vary with the quantity of waste and the pattern of its discharge from the factory. • Most basins are rectangular or square.
  26. 26. Effect of equalization
  27. 27. Capacity and Detention period of ET • The capacity should be adequate to hold, and render homogeneous, all the waste from the plant. • Almost all industrial plants operate on a cycle basis; • Thus, if the cycle of operations is repeated every 2 hours, an equalization tank that can hold a 2-hour flow will usually be sufficient. • If the cycle is repeated only every 24 hours, the equalization basin must be big enough to hold a 24-hour flow of waste.
  28. 28. • This mixing may be brought about in the following ways: (1) proper distribution and baffling; (2) mechanical agitation; (3) aeration; and (4) combinations of all three.
  29. 29. Baffling
  30. 30. • Proper distribution and baffling is the most economical, though usually the least efficient, method of mixing. • Still, this method may suffice for many plants. • Horizontal distribution of the waste is achieved by using either several inlet pipes, spaced at regular intervals across the width of the tank, or a perforated pipe across the entire width. • Over and under baffles are advisable when the tank is wide because they provide more efficient horizontal and vertical distribution.
  31. 31. Mechanical Agitators
  32. 32. • Mechanical agitation eliminates most of the need for baffles and generally provides better mixing than baffles alone. • One typical arrangement, shown in Figure, uses three wooden gate type agitators spaced equidistantly along the centre line of the length of the tank. • Agitators operated at a speed of 15 rotations/min (rpm) by a 3-horsepower (hp) motor are usually adequate.
  33. 33. Types of equalization tank In-Line Equalization tank
  34. 34. Side –Line or Off-Line equalization tank
  35. 35. Volume of Equalization Tanks Volume can be determined by Mass Curve Method
  36. 36. Proportioning • Proportioning means the discharge of industrial wastes in proportion to the flow of municipal sewage in the sewers or to the stream flow in the receiving river. • In most cases, it is possible to combine equalization and proportioning in the same basin. • The effluent from the equalization basin is metered into the sewer or stream according to a predetermined schedule. • The objective of proportioning in sewers is to keep constant the percentage of industrial wastes to domestic sewage flow entering the municipal sewage plant.
  37. 37. Objectives • To protect municipal sewage treatment using chemicals from being impaired by a sudden overdose of chemicals contained in the industrial waste • To protect biological treatment devices from strong loads of industrial wastes , which may inactivate the bacteria • To minimize fluctuations of sanitary standards in the treated effluent
  38. 38. • The rate of flow of industrial waste varies from instant to instant, as does the flow of domestic sewage, and both empty into the same sewage system. • Therefore, the industrial waste must be equalized and retained, and then proportioned to the sewer or stream according to the volume of domestic sewage or stream flow. • To facilitate proportioning, a holding tank should be constructed with a variable-speed pump to control the effluent discharge.
  39. 39. • There are two general methods of discharging industrial waste in proportion to the flow of domestic sewage at the municipal plant: 1. manual control related to a well defined domestic sewage flow pattern, and 2. automatic control by electronics.
  40. 40. Manual Control • Manual control is lower in initial cost but less accurate. • It involves determining the flow pattern of domestic sewage for each day of the week over a period of months. • Usually one does this by examining the flow records of the sewage plant or by studying the hourly water-consumption figures for the city. • It is better to spend time on a careful investigation of the actual sewage flow than to make predictions based on miscellaneous non pertinent records. • Actual investigative data should be used to support those records that are applicable to the case.
  41. 41. Automatic Control • Automatic control of waste discharge according to sewage flow involves placing a metering device that registers the amount of flow at the most convenient main sewer connection. • This device translates the rate of flow in the sewer to a recorder located near the plant’s holding tank. • The pen on the recorder actuates either a mechanical (gear) or a pneumatic (air) control system for opening or closing the diaphragm of the pump. • There are, of course, many variations of automatic flow-control systems. Although their initial cost is higher than that of manual control, they will usually return the investment many times by the savings in labour costs.
  42. 42. Flowsheet with Equalization Tank 1
  43. 43. Flowsheet with Equalization Tank 2
  44. 44. Online Lecture - 14 Industrial Wastewater Treatment and management Wastewater Treatments Module-III 57
  45. 45. Definition of pH • By definition pH is the measure of free hydrogen ion concentration in water and can be expressed as pH= -log[H+]
  46. 46. pH Scale
  47. 47. What is Neutralization? • Neutralization involves adjusting the pH of a liquid to approach the “neutral” pH of 7.0 (neither acid nor base). • Generally, neutralization involves the use of an acid (pH less than 7) to lower the pH of a tank of basic (or alkaline) liquid (pH greater than 7), • or the use of abase (or alkali) to raise the pH of a tank of acidic liquid
  48. 48. Concept of Neutralization
  49. 49. NEUTRALIZATION • Excessive acid or alkaline wastes should not be discharged without treatment into a receiving stream. There are many acceptable methods for neutralizing over-acidity or over-alkalinity of wastewaters such as : i) Mixing wastes ; ii) Limestone treatment for acid waste ; iii) Lime slurry treatment for acid waste ; iv) Caustic Soda treatment for acid waste ; v) Waste-boiler - Flue-Gas ; vi) CO2 treatment for alkaline waste ; vii) Producing CO2 in alkaline wastes ; and viii) Sulfuric acid treatment for alkaline waste.
  50. 50. 1. Mixing of wastes • Mixing of wastes can be accomplished within a single plant operation or between neighbouring industrial plants. • Acid and alkaline wastes may be produced. Individually within one plant and proper mixing of these waste at appropriate time. results in neutralization. • For example, if one plant produces an alkaline waste which can be pumped conventionally to an area adjacent to a plant discharging an acid waste, an economical and feasible system of neutralization results for each plant.
  51. 51. Industry A Producing Acidic waste Industry B Producing Alkaline waste Neutralization
  52. 52. A. Neutralization of Acidic Waste 2. Lime stone treatment for acid wastes • In this method, acid wastes is passed through beds of limestones (CaCO3) at a rate of about one gallon per minute per square feet (1gpm/ft2). • Neutralization takes place with following reaction : CaCO3 + H2SO4 ———————> CaSO4 + H2CO3 • This reaction will continue as long as excess limestone is available and in an active state. • Disposing of the used limestone beds can be a serious drawback to this method of neutralization.
  53. 53. • Since the used limestone must be replaced by fresh at periodic interval, frequency of replacement depending on the quantity and quality of acid wastes being passed through a bed. • When there are extremely high acid loads, foaming may occur, especially when organic matter is also present in the waste.
  54. 54. 3. Lime-slurry treatment for acid wastes • Mixing acid wastes with lime slurries is an effective procedure for neutralization. The reaction is similar to that obtained with limestone beds But the advantages of using lime slurry than lime stone beds are : i) In this case, lime is used up continuously because it is converted to CaSO4 and which is carried out in the waste ; ii) Lime possesses a high neutralizing power and its action can be hastened by heating or by oxygenating the mixture. iii) It is relatively inexpensive, but in large quantities the cost can be an important item.
  55. 55. Lime slurry neutralization
  56. 56. 4. Caustic-Soda treatment for acid wastes • Concentrated solutions of caustic soda or sodium carbonate cause neutralization of acid waste. These neutralizers are more powerful than • lime or limestone and some agents are required in small volume. • Another advantage is that the reaction products are soluble and thus they do not increase the hardness of receiving waters. • When sodium hydroxide is used as a neutralizing agent for carbonic and sulfuric acid wastes, the following reactions take place : • Na2CO3 + CO2 + H2O →2NaHCO3 Carbonic Acid Waste
  57. 57. 2NaOH + CO2 →NaHCO3 + H2O NaOH + H2SO4 → NaHSO4 + H2O Sulfuric Acid Waste NaHSO4 + NaOH →Na2SO4 + H2O • Both these neutralizations take place in two steps and the end products depend on the final pH desired.
  58. 58. 5. Neutralization of Alkaline Wastes : Using Waste- Boiler-Fuel Gas • It is a most economical method for neutralization of alkaline waste. • In this method, when waste boiler-flue gas (containing 14 percent CO2) is passed through the alkaline waste CO2 dissolve in waste water and will form carbonic acid (a weak acid) which in turn reacts with caustic wastes to neutralize the excess alkalinity as follows : i. CO2 + H2O→ H2CO3 Flue gas + Waste Water Carbonic acid ii. H2CO3 + 2NaOH→ Na2CO3 + 2H2O Carbonic acid Soda ash iii. H2CO3 + Na2CO3 →2NaHCO3 + H2O Excess Soda ash Sodium Carbonic Acid in waste bicarbonate in waste
  59. 59. CO2 Production
  60. 60. CO2 storage for neutralization
  61. 61. Flue gas Neutralization
  62. 62. 6 Carbon - Dioxide Treatment for Alkaline Wastes • Bottled CO2 is applied to wastewaters which neutralizes alkaline wastes on the same principle as boiler-flue gas [i.e. it forms a weak acid (carbonic acid) dissolved in water. • When the quantity of alkaline waste is large, there is operational difficulty as well as high cost.
  63. 63. 7 Producing Carbon-dioxide in Alkaline Wastes • CO2 produced by fermentation of an alkaline, organic waste help in neutralization of alkaline waste by decreasing the pH. • Similar by fermenting alkaline fat-sugar wastes with yeast, CO2 is produced which can be used for neutralization.
  64. 64. 8 Sulfuric-Acid Treatment for Alkaline Wastes • The addition of sulfuric acid to alkaline wastes causes neutralization. • In this method, storage and feeding equipment requirement are low due to high acidity value of Na2S04, but it is difficult to handle because of its corrosiveness. • The neutralization reaction which occurs, when it is added to wastewater is as follows : • 2NaOH + H2SO4 → Na2SO4 + 2H2O
  65. 65. pH calculations
  66. 66. Online Lecture - 14 Industrial Wastewater Treatment and management Wastewater Treatments Module-III 82
  67. 67. Key for pH problems
  68. 68. Find pH of mix if two equal volume wastes are mixed together with pH 6 and 4 respectively.
  69. 69. Assignment 5 Module III Q1. Differentiate between sewage and Industrial wastewater. Q2. Discuss control of industrial pollution in detail. Q3. Explain Equalization and proportioning. Q4. Enlist methods used for neutralization of acidic and alkaline wastes. Explain any one method in detail. Q5.
  70. 70. Q6. Determine pH of two industrial wastes having pH 6 and 8 respectively. Assume equal volumes of waste are mixed together.
  71. 71. MCQs 1. Industrial waste water treatment is required for _____________. (to protect receiving water, recycling of wastewater, recovery of valuables) 2. Organic content in industrial wastewater may deplete____ in river water. 3. Oil and grease if discharged in wastewater interferes with ______. 4. Equalisation tank can be used for tackling fluctuations in ________ and _______. 5. ____________ and ______________ are types of equalization tanks.
  72. 72. 6. Proportioning is method of discharging industrial waste in proportion with discharge of ________ or ___________. 7. _______ method of proportioning id cheap but not accurate. 8. If proportioning of industrial wastewater is not done w.r.t. sewer discharge, then it may affect ________processes and reduce its efficiency. 9. pH +pOH = ____. 10. __ gas can be used for neutralization of alkaline waste. 11. ___________ process of acidic waste neutralization produces more quantity of sludge. 12. Lime slurry process of neutralization is _____than lime stone method.

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