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Module IV Wastewater treatment methods

DABTU Wastewater Treatment T E (CIVIL)

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Module IV Wastewater treatment methods

  1. 1. Online Lecture 16 Waste Water Treatment Methods Waste Water Treatments Module IV
  2. 2. Contents • Nitrification and De-nitrification – Phosphorous removal – Heavy metal removal – Membrane Separation Process– Reverse osmosis– Chemical Oxidation–Ion Exchange – Air Stripping and Absorption Processes – Special Treatment Methods –Disposal of Treated Waste • Common Effluent Treatment Plants (CETPs): Need, Planning, Design, Operation & Maintenance Problems
  3. 3. Sambhaji Lake, Solapur Eutrophication
  4. 4. Introduction • Urine, human excreta, and food processing wastes are the primary sources of nitrogen for municipal wastewater. • Domestic wastewater typically has a total nitrogen content that is about one-fifth of the biochemical oxygen demand (BOD), with typical nitrogen concentrations ranging from 20 to 70 mg/L. • About 60% to 70% is ammonia-nitrogen, and 30% to 40% percent is organic nitrogen, with less than 1% nitrite and nitrate nitrogen
  5. 5. A. Nitrification • Nitrification is an oxidation process (loss of electrons or gain of the oxidation state by an atom or compound takes place). • This process starts with the ammonium which gets oxidized into nitrite (NO2 -), this action is performed by the bacteria Nitrosomonas sp. • Later on, this nitrite (NO2-) gets oxidized into nitrate (NO3 -), and this action is performed by the Nitrobacter sp.
  6. 6. • The bacteria are autotrophic, and the reaction is performed under aerobic condition. • The importance of this step in the nitrogen cycle is the conversion of ammonia into nitrate, as nitrate is the primary nitrogen source present in the soil, for the plant. • Though nitrate is toxic to the plants. • The activity of nitrifying bacteria gets slower in acidic solution, and are best at pH between 6.5 to 8.5 and temperature vary from 16 to 35°C.
  7. 7. B. Denitrification • Denitrification is the reduction process, where the nitrate is removed in the form of nitrogen and is converted to nitrogen gas. • The action is performed by bacteria like Bacillus, Aerobacter, Lactobacillus, Spirillum, Pseudo mona
  8. 8. • The bacteria are heterotrophs, and the action is completed under anaerobic condition. • Even the small amount of oxygen may hamper the process, but there is a need of organic carbon. • Denitrification is useful for wastewater treatment, aquatic habitats. • The denitrification is performed best at pH between 7.0 to 8.5 and at the temperature between 26 to 38°C.
  9. 9. In Short • The biological process where ammonium (NH4+) is oxidized and converted into the nitrate (NO3-) is called as nitrification, while denitrification is biological process involves the conversion of nitrate (NO3 -) into nitrogen gas (N2). • The precursor of the nitrification process is ammonia, and the end product is nitrate, whereas nitrate is the precursor of the denitrification process and nitrogen is the end product.
  10. 10. Differentiation between Nitrification and Denitrification BASIS FOR COMPARISON NITRIFICATION DENITRIFICATION Meaning The part of nitrogen cycle where ammonium (NH4+) is converted into nitrate (NO3-) is called nitrification. Denitrification is the level where reduction of nitrate (NO3-) is made into nitrogen gas (N2). The process involves Nitrifying bacteria like Nitrobacter, Nitrosomonas. Denitrifying bacteria like Spirillum, Lactobacillus, Pseudomonas, Thiobacillus. Grows slowly. Grows rapidly. Requires aerobic condition. Requires anaerobic condition.
  11. 11. The microbes Autotrophic. Heterotrophic. Precursor Ammonium . Nitrate. End product Nitrate. Nitrogen. pH and Temperature The process occurs at the pH between 6.5 to 8.5 and temperature between 16 to 35 degree C. The process occurs at the pH between 7.0 to 8.5 and temperature between 26 to 38 degree C. Importance Provides nitrate to the plant, which acts as the important nitrogen source. Denitrification is used in wastewater treatment and is beneficial for aquatic habitats.
  12. 12. Flowsheet -1
  13. 13. Flow sheet - 2
  14. 14. Flow sheet -3
  15. 15. Flow sheet -4
  16. 16. Phosphorus Removal
  17. 17. • Controlling phosphorous discharged from municipal and industrial wastewater treatment plants is a key factor in preventing eutrophication of surface waters. • Phosphorous is one of the major nutrients contributing in the increased eutrophication of lakes and natural waters. • Phosphate removal is currently achieved largely by chemical precipitation, which is expensive and causes an increase of sludge volume by up to 40%. An alternative is the biological phosphate removal (BPR).
  18. 18. 1. Chemical methods • Phosphate precipitation • Chemical precipitation is used to remove the inorganic forms of phosphate by the addition of a coagulant and a mixing of wastewater and coagulant. The multivalent metal ions most commonly used are calcium, aluminium and iron. 1) Calcium: • it is usually added in the form of lime Ca(OH)2. It reacts with the natural alkalinity in the wastewater to produce calcium carbonate, which is primarily responsible for enhancing SS removal. • Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 ↓+ 2H2O • Akalinity lime calcium carbonate ppt
  19. 19. • As the pH value of the wastewater increases beyond about 10, excess calcium ions will then react with the phosphate, to precipitate in hydroxylapatite: • 10 Ca2+ + 6 PO4 3- + 2 OH- ↔ Ca10(PO4)*6(OH)2 ↓ • Because the reaction is between the lime and the alkalinity of the wastewater, the quantity required will be, in general, independent of the amount of phosphate present. • It will depend primarily on the alkalinity of the wastewater. • Neutralisation may be required to reduce pH before subsequent treatment or disposal.
  20. 20. 2) Aluminium and Iron: • Alum or hydrated aluminium sulphate is widely used precipitating phosphates and aluminium phosphates (AlPO4). The basic reaction is: • Al3+ + HnPO4 3-n ↔ AlPO4 + nH+ • Ferric chloride or sulphate and ferrous sulphate also know as copperas, are all widely used for phosphorous removal. The basic reaction is: • Fe3+ + HnPO4 3-n ↔ FePO4 + nH+ • Ferric ions combine to form ferric phosphate (FePO4). • They react slowly with the natural alkalinity and so a coagulant aid, such as lime, is normally add to raise the pH in order to enhance the coagulation.
  21. 21. Strategies The main phosphate removal processes are (see picture): 1.Treatment of raw/primary wastewater 2.Treatment of final effluent of biological plants (postprecipitation) 3.Treatment contemporary to the secondary biologic reaction (co-precipitation).
  22. 22. 2. Biological Removal • The principal advantages of biological phosphorous removal are reduced chemical costs and less sludge production as compared to chemical precipitation. • In the biological removal of phosphorous, the phosphorous in the influent wastewater is incorporated into cell biomass, which is subsequently removed from the process as a result of sludge wasting.
  23. 23. • The reactor configuration provides the P accumulating organisms (PAO) with a competitive advantage over other bacteria. • So PAO are encouraged to grow and consume phosphorous. • The reactor configuration in comprised of an anaerobic tank and an activated sludge activated tank. •
  24. 24. • In the anaerobic zone: Under anaerobic conditions, PAO assimilate fermentation products (i.e. volatile fatty acids) into storage products within the cells with the concomitant release of phosphorous from stored polyphosphates. • Acetate is produced by fermentation of COD, which is dissolved degradable organic material that can be easily assimilated by the biomass. •
  25. 25. • Using energy available from stored polyphosphates, the PAO assimilate acetate and produce intracellular polyhydroxybutyrate (PHB) storage products. • Concurrent with the acetate uptake is the release of orthophosphates, as well as magnesium, potassium, calcium cations. • The PHB content in the PAO increases as the polyphosphate decreases.
  26. 26. • In the aerobic zone: energy is produced by the oxidation of storage products and polyphosphate storage within the cell increases. • Stored PHB is metabolized, providing energy from oxidation and carbon for new cell growth. Some glycogen is produced from PHB metabolism. • The energy released from PHB oxidation is used to form polyphosphate bonds in cell storage. •
  27. 27. • The soluble orthophosphate is removed from solution and incorporated into polyphosphates within the bacterial cell. • PHB utilisation also enhances cell growth and this new biomass with high polyphosphate storage accounts for phosphorous removal. • As a portion of the biomass is wasted, the stored phosphorous is removed from the biotreatment reactor for ultimate disposal with the waste sludge.
  28. 28. O2
  29. 29. Flowsheet for Phosphorus removal
  30. 30. Online Lecture 17 Waste Water Treatment Methods Waste Water Treatments Module IV
  31. 31. Contents • Nitrification and De-nitrification – Phosphorous removal – Heavy metal removal – Membrane Separation Process– Reverse osmosis– Chemical Oxidation–Ion Exchange – Air Stripping and Absorption Processes – Special Treatment Methods –Disposal of Treated Waste • Common Effluent Treatment Plants (CETPs): Need, Planning, Design, Operation & Maintenance Problems
  32. 32. Heavy metal removal • Methods for treating industrial wastewater containing heavy metals often involve technologies for reduction of toxicity in order to meet technology-based treatment standards. • Physico-chemical removal processes such as; 1. Adsorption, 2. Ion exchange, 3. Membrane filtration- Reverse Osmosis (RO) 4. Electrodialysis,
  33. 33. 1. Adsorption • Recently this process is recognized widely for removal of heavy metals from wastewater. • Many cheap adsorbents had been developed lately. • These adsorbents are widely use for treatment of wastewater containing heavy metals. • These adsorbents are derived from the waste products generated from industrial activities, waste generated from agriculture and natural materials. • Adsorption can be defined as a mass transfer process which transfers the substance from the liquid phase to the surface of a solid and becomes bound by physical and chemical interactions.
  34. 34. • It’s a three-step treatment process 1 the pollutant is transferred to the sorbent surface from bulk solution 2 adsorption on particle surface 3 transportation within the sorbent particle.. • This technique is very cost effective. 1.Adsorption on modified natural materials 2.Adsorption on industrial by-products 3.Bio-sorption
  35. 35. Adsorption • One of the most commonly used techniques for removing organics and heavy metals involves the process of adsorption, which is the physical adhesion of chemicals on to the surface of the solid. • The effectiveness of the adsorbent is directly related to the amount of surface area available to attract the particles of contaminant.
  36. 36. • The most commonly used adsorbent is a very porous matrix of granular activated carbon, which has an enormous surface area ( @1000 m2/g). • Adsorption on activated carbon is perhaps the most economical and technically attractive method available for removing soluble organics such as phenols, chlorinated hydrocarbons, surfactants, and colour (dyes) and odour producing substances from waste water.
  37. 37. • adsorbate: material being adsorbed. • Adsorbent: material doing the adsorbing. (examples are activated carbon or ion exchange resin). • Generally some combination of physical and chemical adsorption is responsible for activated carbon adsorption in water and wastewater.
  38. 38. Physical adsorption: • Van der Waals attraction between adsorbate and adsorbent. • The attraction is not fixed to a specific site and the adsorbate is relatively free to move on the surface. • This is relatively weak, reversible, adsorption capable of multilayer adsorption.
  39. 39. Chemical adsorption: • Some degree of chemical bonding between adsorbate and adsorbent characterized by strong attractiveness. Adsorbed molecules are not free to move on the surface. • There is a high degree of specificity and typically a monolayer is formed. • The process is rarely reversible.
  40. 40. 2. MEMBRANE TECHNOLOGY
  41. 41. Membrane technologies
  42. 42. Difference between Osmosis and RO
  43. 43. Reverse Osmosis
  44. 44. • Reverse osmosis (RO) is a membrane-technology filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. • The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. • To be "selective," this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely.
  45. 45. • Commonly used membrane is Cellulose Acetate • Pre-treatment of wastewater is needed to avoid membrane fouling. • High COD and BOD can also affect membrane. • Flushes away impurities and does not collect them. • It can remove almost everything. It allows only water (H2O) to pass • Very efficient but Cost is high • Can remove everything from water and wastewater.
  46. 46. RO PLANT
  47. 47. RO MEMBRANE
  48. 48. Applications of RO • Applications include treatment and recycle of wastewaters generated from metal finishing and plating operations; printed circuit board and semiconductor manufacturing (treatment and recycle of rinse waters used in electroplating processes); automotive manufacturing (treatment and recycle of water used for cleaning and painting); food and beverage (concentration of wastewater for reuse and reduction of BOD prior to discharge); groundwater and landfill leachate (removal of salts and heavy metals prior to discharge).
  49. 49. 3. Electrodialysis • Electrodialysis is an electrochemical process whereby electrically charged particles, ions, are transported from a raw solution (retentate, diluate) into a more concentrated solution (permeate, concentrate) through ion-selective membranes by applying an electric field. • When a salt solution is under the influence of an electric field, as is the case in an electrodialysis module, the charge carriers in the solution come into motion.
  50. 50. • This means that the negatively charged anions migrate towards the anode and the positively charged cations towards the cathode. • In order to separate salts from a solution, ion-selective membranes, through which only one type of ion can permeate in an ideal case, are arranged in the solution perpendicular to the electric field.
  51. 51. • Thus negatively charged particles (anions) can pass through an anion exchange membrane on their way to the anode but are selectively retained by the upstream cation exchange membrane. • This separation stage results in a concentration of electrolytes in the so-called concentrate loop and a depletion of charge carriers in the so-called diluate loop.
  52. 52. Applications 1. Nitrogen removal from drinking water (nitrate, ammonium) 2. Desalination of organic substances 3. Concentration of salts, acids and bases 4. Removal of heavy metals
  53. 53. 4. Ion exchange • This technique has been used extensively to remove hardness, and iron and manganese salts in drinking water supplies. • It has also been used selectively to remove specific impurities and to recover valuable trace metals like chromium, nickel, copper, lead and cadmium from industrial waste discharges.
  54. 54. • For example: NiSO4 + Ca(OH)2 →Ni(OH)2 + CaSO4 • In this reaction, the nickel ions of the nickel sulphate (NiSO4) are exchanged for the calcium ions of the calcium hydroxide Ca(OH)2 molecule. • Similarly, a resin with hydrogen ions available for exchange will exchange those ions for nickel ions from the wastewater solution. The reaction can be written as follows: (R–SO3H)2 + NiSO4 = (R-SO3)2Ni + H2SO4 • R indicates the organic portion of the resin and SO3 is the immobile portion of the ion active group.
  55. 55. • Two resin sites are needed for nickel ions with a plus 2 valence (Ni+2). Trivalent ferric ions would require three resin sites. (R–SO3)2Ni + H2SO4 –> 2(R-SO3H) + NiSO4 • This step is known as regeneration. • In general terms, the higher the preference a resin exhibits for a particular ion, the greater the exchange efficiency in terms of resin capacity for removal of that ion from the wastewater solution. • Greater preference for a particular ion, however, will result in increased consumption of chemicals for regeneration.
  56. 56. Online Lecture 18 Waste Water Treatment Methods Waste Water Treatments Module IV
  57. 57. Contents • Nitrification and De-nitrification – Phosphorous removal – Heavy metal removal – Membrane Separation Process– Reverse osmosis– Chemical Oxidation–Ion Exchange – Air Stripping and Absorption Processes – Special Treatment Methods –Disposal of Treated Waste • Common Effluent Treatment Plants (CETPs): Need, Planning, Design, Operation & Maintenance Problems
  58. 58. 1. Air Stripping • Air stripping is a technique in which wastewater and air are intensively brought in contact with each other. • This causes the volatile compounds present in wastewater to be transferred into the air. • The air containing VOC must be treated in an air treatment system. • A stripper only needs a small surface area; 5x5 m2 is sufficient for a stripper with a capacity of 100 m3/hour.
  59. 59. • The space taken by an air treatment unit varies greatly. • The main set-up types are the stripping tower or stripping column and the plate stripper. • The stripping tower is based on the counter-flow principle, where a vertical column is filled with packing material. • The plate stripper is based on the cross-flow principle, where the liquid flow is intensively aerated via a perforated plate. • The stripping process is cheap and reliable, and provides relatively good substance transfer. One of the disadvantages of this process is that it is susceptible to pollution.
  60. 60. Air Stripping Packing material
  61. 61. Application • In both inorganic and organic chemistry, stripping is used for the removal of volatile organic substances, sulphur compounds (H2S, phosphine) and NH3. Stripping is normally carried out on the concentrated partial flow; • Air stripping is used in the pharmaceutical sector for the removal of chlorinated solvents from wastewater; • Air stripping is primarily implemented for the removal of volatile organic matter (incl. chlorinated hydrocarbons) from wastewater. • In a variety of sectors, air stripping is implemented for the removal of chlorinated solvents from wastewater:
  62. 62. Disadvantage • Air containing VOC is released. • Air treatment could possibly be needed (e.g. active carbon system, bio-filter). • Depending on the influent, the location and the installation, extra measures may be needed to prevent odour and noise problems.
  63. 63. MBBR , SBR AND MBR
  64. 64. 2. MBBR - Moving Bed Bio-Reactors Process Description • MBBRs biologically treat wastewater by circulating moving media in aerobic, activated-sludge environments. • The moving media is typically a floating plastic substrate colonized by a community of bacteria. • These bacteria form a biofilm on the plastic surface. Increased levels of biofilm enhance the biological treatment process by introducing a more robust microbial community. • In addition to the biofilm attached to the plastic carriers, biomass in the system also exists in the form of suspended flocks. • At smaller scales* in India, MBBR tanks were found to be constructed of reinforced concrete or mild steel. • Some suppliers also offer fiber reinforced polymer (FRP) tanks.
  65. 65. MBBR
  66. 66. Advantages • Can operate at high organic loads • Is less prone to hydraulic overloading than other STP types • Is relatively easy to operate—does not require advanced skills for operation/maintenance • Generally has lower capital costs than MBR-based systems • Eliminates issues with media becoming clogged (compared to fixed film systems)
  67. 67. Disadvantages • Is a manually operated process • Generally offers a lower level of wastewater treatment than MBR-based systems
  68. 68. Process Description • SBRs are based on the activated-sludge treatment process. SBRs use a batch approach in which secondary sewage treatment occurs in a single tank. • In the first stage of SBR treatment, influent is added to the batch- reactor tank and aerated. • Following aeration, the wastewater is allowed to settle. Finally, the treated wastewater is removed from the top of the tank using a decanter valve, pump, or airlift tube. • At smaller scales*in India, SBR tanks were found to be constructed of reinforced concrete or mild steel. 3. SBR- Sequential Batch reactors
  69. 69. Advantages • Allows for react, settle, and decant phases to occur within the same tank • Does not require secondary clarifiers or return-activatedsludge (RAS) lines • Generally has lower capital costs than MBR-based systems • Is an automated process**
  70. 70. Disadvantages • Can face issues with high peak flows—unless already factored into design • Requires higher skill level for maintenance, due to more complex system setup (automation/instrumentation) • Generally offers a lower level of wastewater treatment than MBR- based systems
  71. 71. 4. Membrane Bioreactor (MBR) • Membrane bioreactors (MBRs) combine two treatments processes: the activated-sludge process and membrane filtration. • Wastewater is first aerated in a bioreactor tank, where microorganisms are present in the form of suspended flocks. • Then, a microporous membrane is used for solid/liquid separation. This configuration eliminates the need for secondary clarifiers. • At smaller scales* in India, MBR tanks were found to be constructed of mild steel. As such, civil costs (or costs associated with constructing reinforced concrete structures—e.g., tanks, foundations) are minimal. • Note that MBRs can also be added to existing MBBRs as retrofits.
  72. 72. Advantages • Generally offers higher level of wastewater treatment than MBBR-or SBR-based systems • Does not require secondary clarifiers • Is an automated process**
  73. 73. Disadvantages • Typically has higher capital costs than MBBR-or SBR-based systems • Requires membrane replacement approximately every 3 years • Requires higher skill level for maintenance, due to more complex system setup (automation/instrumentation)
  74. 74. 5. Common Effluent Treatment Plants (CETP) • The concept of common effluent treatment plant has been accepted as a solution for collecting, conveying, treating, and disposing of the effluents from the industrial estates. • The effluent include industrial wastewaters and domestic sewage generated from the estate. • This CETP concept helps small and medium scale industries to dispose of their effluents. Otherwise it may not be economical for these industries to treat their wastewaters or there may be space constraints. • Some of these industries may require to give preliminary treatment (for removal of solids) so that the receiving sewers can be maintained free flowing. •
  75. 75. • It may be required to correct pH or removal of specific pollutant before the industry discharges in CETP • CETP is designed on the basis of: – Quality and flow rate of the wastewater. – Effluent standard required by CETP. – Possibility of recycle and reuse of treated wastewater. – Availability of land, manpower, energy and expertise in specific treatment methods. – Willingness of the industries located in the industrial estate to contribute towards the capital and operating expenses of CETP.
  76. 76. • CETPs are classified in two categories – • (i) Homogenous : Industries producing similar goods in that industrial area are contributing. E.g., tanneries, paper, etc. • (ii) Heterogenous : industries producing widely divergent goods are placed together. E.g., chemical, dairy, soft drink, canneries, pharmaceuticals, etc. • Designing the treatment plant for the former is easier than the later due to difficulty in estimating characteristics of the combined wastewater.
  77. 77. Advantages of providing CETP – Small and medium scale industries are not required to treat their wastewater separately. – Assured wastewater treatment hence better control over pollution. – Concerned pollution control agency have to monitor only one treatment plant for its performance. – Participating industries have commitment to generate wastewaters acceptable to CETP. – Industries are responsible for finding ways to minimize pollution load and reduce water consumption to the extent possible.
  78. 78. Drawbacks – There could be conflict among the industries about the wastewater quality and quantity on which the cost of treatment depends. – Failure of pay may result in not allowing this industry to discharge wastewater.
  79. 79. Sample Flow sheet
  80. 80. Objective questions 1. Pick out the odd one i. Microfiltration, filtration, Nanofiltration, adsorption. 2. _______________ membrane is commonly used in RO process. 3. ____________ ________ is excellent adsorbent because of its very high surface area. 4. For RO, pretreatment is needed to avoid ________ _________. 5. ___________ and __________ are types of CETPs. 6. ______________combine two treatments processes: the activated- sludge process and membrane filtration.
  81. 81. 7. ___________ use a batch approach in which secondary sewage treatment occurs in a single tank. 8. MBBRs biologically treat wastewater by circulating ______media in aerobic, activated-sludge environments. 9. __________ technique is used to remove hardness and heavy metals from water and wastewater respectively. 10. Commonly used membrane in RO is ___________. 11. Pre-treatment of wastewater is needed to avoid _____ ______in RO. 12. The biological process where ammonium (NH4+) is oxidized and converted into the nitrate (NO3-) is called as ___________, while _________ is biological process involves the conversion of nitrate (NO3 -) into nitrogen gas (N2).
  82. 82. Theory Questions Q1. Write Short note on 1. Electrodialysis 2. Reverse Osmosis 3. Ion Exchange 4. CETP 5. MBBR 6. SBR 7. MBR Q2. Differentiate between Physical adsorption and Chemical Adsorption Q3. Explain Nitrification and Denitrification Q4. Explain Phosphorus removal from wastewater.

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