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Nitrification and Treatment Plants

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Nitrification and Treatment Plants

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Nitrification and Treatment Plants

  1. 1. Wastewater Treatment Plant A WWTP is the place where wastewater is treated to remove pollutants before it enters a water body or reused. It includes physical , chemical & biological processes to remove physical , chemical and biological contaminations.
  2. 2. Forms Of Nitrogen In Wastewater • Ammonia – NH3 • Nitrite – NO2 - • Nitrate – NO3 - • Organic nitrogen
  3. 3. • Total Kjeldal Nitogen-TKN Sum of organic nitrogen + ammonia • Total Inorganic Nitrogen-TIN Sum of Ammmonia + Nitrite + Nitrate
  4. 4. Why is it necessary to treat the forms of nitrogen? • Improve receiving stream quality • Increase chlorination efficiency • Minimize pH changes in plant • Increase suitability for reuse
  5. 5. • Prevent ammonia toxicity • Protect groundwater from nitrate contamination • To control the growth of algae • To prevent the DO depletion • Odor problems
  6. 6. • To prevent imbalance of natural ecological systems and increase of eutrophication • increase risks to human health, such as NO3-N concentration in the groundwater for potable use.
  7. 7. • Nitrification is the biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of the nitrite to nitrate
  8. 8. Nitrification NH3-N Ammonia N NO2-N Nitrite N NO2-N Nitrite N NO3-N Nitrate N Nitrosomonas Nitrobacter Nitrification of Ammonia Occurs in Two Steps
  9. 9. Heterotrophic Bacteria Break Down Organics Generate NH3, CO2, and H2O Autotrophic Bacteria Utilize Inorganic Compounds (and CO2 as a Carbon Source) Assimilation Some Nitrogen Will Be Removed By The Biomass
  10. 10. Nitrogen cycle Nitrogen is present in the environment in a wide variety of chemical forms including • ammonium (NH4 +) • nitrite (NO2 -) • nitrate(NO3 -) • nitric oxide (NO) or • nitrous oxide (N2O) • inorganic nitrogen gas (N2) • organic nitrogen
  11. 11. • Organic nitrogen may be in the form of a living organism, humus or in the intermediate products of organic matter decomposition. • The processes of the nitrogen cycle transform nitrogen from one form to another. • Many of those processes are carried out by microbes, either in their effort to harvest energy or to accumulate nitrogen in a form needed for their growth.
  12. 12. The processes of Nitrogen cycle 1. Nitrogen Fixation 2. Assimilation 3. Ammonification 4. Nitrification 5. Denitrification N- CYCLE
  13. 13. Nitrogen Fixation • Some fixation occurs in lightning strikes, but most fixation is done by free-living or symbiotic bacteria known as diazotrophs • These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen to produce ammonia , which is converted by the bacteria into other organic compounds • Example of N-fixing bacteria includes:  free-living bacteria is Azotobacter  Symbiotic nitrogen-fixing bacteria such as Rhizobium usually live in the root nodules of legumes
  14. 14. Assimilation • Plants take nitrogen from the soil by absorption through their roots in the form of either nitrate ions or nitrite ions • Plants cannot assimilate ammonium ions • nitrate is absorbed, & reduced to nitrite ions and then ammonium ions for incorporation into amino acids, nucleic acids, and chlorophyll • Animals, fungi, and other heterotrophic organisms obtain nitrogen by ingestion of aminoacids, nucleotides and other small organic molecules
  15. 15. Nitrification • Nitrification is a microbial process by which reduced nitrogen compounds (primarily ammonia) are sequentially oxidized to nitrite and nitrate • The conversion of ammonia to nitrate is performed primarily by soil-living bacteria and other nitrifying bacteria • The nitrification process is primarily accomplished by two groups of autotrophic nitrifying bacteria
  16. 16. In the first step of nitrification, ammonia-oxidizing bacteria oxidize ammonia to nitrite according to equation NH3 + O2 → NO2 - + 3H+ + 2e- Nitrosomonas is the most frequently identified genus associated with this step, although other genera, including Nitrosococcus, and Nitrosospira
  17. 17. In the second step of the process, nitrite-oxidizing bacteria oxidize nitrite to nitrate NO2 - + H2O → NO3 - + 2H+ +2e- Nitrobacter is the most frequently identified genus associated with this second step, although other genera, including Nitrospina, Nitrococcus, and Nitrospira can also autotrophically oxidize nitrite
  18. 18. Denitrification Denitrification is the reduction of nitrates back into the largely inert nitrogen gas (N2), completing the nitrogen cycle. This process is performed in anaerobic conditions
  19. 19. Total Kjeldahl Nitrogen (TKN) NITROGEN CYCLE
  20. 20. PHYSICO-CHEMICAL NITROGEN REMOVAL  Physico-chemical methods of nitrogen removal have not been widely applied in waste water treatment because  They are generally more expensive to operate than biological treatment;  they produce a poorer effluent quality than biological treatment
  21. 21. Air stripping of Ammonia As the pH increases, a greater proportion of ammonia converts fromNH4to NH3 NH3+H20 NH4 + OH
  22. 22. Ion exchange Zeolites have been found effective in waste water treatment as molecular filters which can distinguish molecules at the ionic level. For example, the natural zeolite clinoptilolite is selective for the ammonium ion in preference to other ions present in solution. A filtered waste water can be passed through a bed of zeolite to effect a 90- 97% ammonium removal
  23. 23. Breakpoint chlorination By adding chlorine to a wastewater, a stepwise reaction takes place which results in the conversion of ammonium to nitrogen gas
  24. 24. N Secondary “Treatment” (Biological) WASTEWATER “TREATMENT” Of Nitrogen
  25. 25. APPROACHES TO SECONDARY TREATMENT Fixed Film Systems Suspended Film Systems Lagoon Systems organic matter + O2  CO2 + NH3 + H2O NH3  NO3 - aquatic nutrient
  26. 26. • Biofilm – a biological slime layer – bacteria in biofilm degrade organics – biofilm will develop on almost anything
  27. 27. Stir & suspend microorganisms in waste water. They absorb organic matter &nutrients from waste water. After hours, they settle as sludge…….. Ex…..activated sludge system..etc
  28. 28.  Consist of in-ground earthen basins in which the waste is detained for a specified time and then discharged.  They take advantage of natural aeration and microorganisms in the wastewater to remove sewage.
  29. 29. Can be achieved in any • Aerobic-biological process at low organic loadings • Suitable environmental conditions Nitrifying bacteria are slower growing than the heterotrophic bacteria Key requirement for nitrification to occur, therefore, is that the process should be so controlled that the net rate of accumulation of biomass is less than the growth rate of the nitrifying bacteria
  30. 30. 1. • Trickling Filters 2. • Rotating Biological Contractor 3. • Fixed Bed Reactor 4. • Conventional Activated Sludge Processes at Low Loadings 5. • Two-stage Activated Sludge Systems with Separate Carbonaceous Oxidation and Nitrification Systems
  31. 31. Wastewater treatment system that • Biodegrades organic matter • Used to achieve nitrification Consists of • a fixed bed of rocks, lava, coke, polyurethane foam, ceramic, or plastic media Aerobic conditions are maintained by splashing, diffusion, and either by forced air flowing through the bed or natural convection of air if the filter medium is porous.
  32. 32. • Not a true filtering or sieving process • Material only provides surface on which bacteria to grow • Can use plastic media –lighter - can get deeper beds (up to 12 m) –reduced space requirement –larger surface area for growth –better air flow –less prone to plugging by accumulating slime
  33. 33. • Tank is filled with solid media – Rocks – Plastic • Bacteria grow on surface of media • Wastewater is trickled over media, at top of tank • As water trickles through media, bacteria degrade BOD • Bacteria eventually die, fall off of media surface • Filter is open to atmosphere, air flows naturally through media • Treated water leaves bottom of tank, flows into secondary clarifier • Bacterial cells settle, removed from clarifier as sludge • Some water is recycled to the filter, to maintain moist conditions
  34. 34. Efficient nitrification (ammonium oxidation) Small land area required
  35. 35. Requires expert design and construction Requires operation and maintenance by skilled personnel Requires a constant source of electricity and constant wastewater flow Flies and odours are often problematic Risk of clogging, depending on pre- and primary treatment Not all parts and materials may be locally available
  36. 36. o Temperature o Dissolved oxygen o pH o Presence of inhibitors o Filter depth o Media type o Loading rate o Wastewater BOD
  37. 37. • A rotating biological contactor or RBC is a biological treatment process used in the treatment of wastewater following primary treatment. • The RBC process involves allowing the wastewater to come in contact with a biological medium in order to remove pollutants in the wastewater before discharge of the treated wastewater to the environment. • A rotating biological contactor is a type of secondary treatment process.
  38. 38. • The first RBC was installed in West Germany in 1960, later it was introduced in the United States and Canada. • In the United States, rotating biological contactors are used for industries producing wastewaters high in Biochemical Oxygen Demand (BOD)(e.g., petroleum industry and dairy industry).
  39. 39. • Microorganisms grow on the surface of the discs where biological degradation of the wastewater pollutants takes place. • It consists of a series of closely spaced, parallel discs mounted on a rotating shaft which is supported just above the surface of the waste water. • Aeration is provided by the rotating action, which exposes the media to the air after contacting them with the wastewater, facilitating the degradation of the pollutants being removed. • Biofilms, which are biological growths that become attached to the discs, assimilate the organic materials in the wastewater.
  40. 40. OPERATION • The rotating packs of disks (known as the media) are contained in a tank or trough and rotate at between 2 and 5 revolutions per minute. • Commonly used plastics for the media are polythene, PVC and expanded polystyrene. • The shaft is aligned with the flow of wastewater so that the discs rotate at right angles to the flow with several packs usually combined to make up a treatment train. • About 40% of the disc area is immersed in the wastewater.
  41. 41. • Biological growth is attached to the surface of the disc and forms a slime layer. The discs contact the wastewater with the atmospheric air for oxidation as it rotates. • The discs consist of plastic sheets ranging from 2 to 4 m in diameter and are up to 10 mm thick. Several modules may be arranged in parallel and/or in series to meet the flow and treatment requirements. • Approximately 95% of the surface area is thus alternately submerged in waste water and then exposed to the atmosphere above the liquid.
  42. 42. • Carbonaceous substrate is removed in the initial stage of RBC. • Carbon conversion may be completed in the first stage of a series of modules, with nitrification being completed after the 5th stage, when the BOD5 was low enough. • Most design of RBC systems will include a minimum of 4 or 5 modules in series to obtain nitrification of waste water. • The rotation of the disks contacts the biomass in the wastewater ,then with the atmosphere for adsorption of oxygen. • Biomass uses the oxygen & organic matter for food thus reducing the BOD in the wastewater.
  43. 43. • Ammonia oxidizers could not effectively compete with the faster-growing heterotrophs that oxidize organic matter. • Nitrification occurs only when the BOD was reduced to approximately 14 mg/L, and increases with rotation speed. • RBC performance was negatively affected by low dissolved oxygen in the first stages and by low pH in the later stages where nitrification occurred.
  44. 44. A schematic cross-section of the contact face of the bed media in a rotating biological contactor (RBC) • The degree of wastewater treatment is related to the amount of media surface area and the quality and volume of the inflowing wastewater.
  45. 45. Fixed Bed Reactor A type of continuous reactor in which the reactants are feed continuously into the reactor at one point, allow the reaction to take place and withdraw the products at another point.
  46. 46. Working Principle • In these reactors, the reaction takes place in the form of a heterogeneously catalyzed gas reaction on the surface of catalysts/in biofilms that are arranged as a so-called fixed bed in the reactor.
  47. 47. Fixed bed reactor: Raschig rings are pieces of tube used in large numbers as a packed bed to support biofilms.
  48. 48. • Ammonia and nitrite oxidizer communities are fixed on the bed material (Raschig rings, Pall rings, Hiflow, Flocor) to form biofilms. • AOB occupied the outside layers of the biofilm, whereas NOB which found in the deep layers of the biofilm • A high cell concentration is possible with immobilized biomass, because of large solids retention time.
  49. 49. Schematic of cross-sectional view of bioflim presenting spatial distribution of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteraia (NOB) species and diffusion of substrate across the biofilm.
  50. 50. Schematic diagram of experimental setup of up-flow fixed- bed reactor
  51. 51. Basics Setup for FBRs • The wastewater reaches the first tank (chamber) of the treatment plant via the inlet sewer. • The second tank absorbs hydraulic fluctuations • A filling pump (pneumatic or electrical) feeds the biological stage evenly (over a period of 24 hours). This ensures that in the event of subsequent load fluctuations the most favourable operating mode can always be set
  52. 52. • Gravity pipes are used to fill standard treatment plants, and there is no buffer pump. • A biological layer (micro-organic colonisation) forms on the fixed-bed material after the start-up period. • The aeration system installed underneath the fixed-bed material supplies the organisms with sufficient air
  53. 53. Ammonia Oxidizers: Ammonia N Nitrite N • Four major groups of ammonia oxidizer microorganisms are known:- • Ammonia-oxidizing Archaea (AOA): e.g Nitrosopumilus maritimus, Nitrososhaera gargensis, Nitrosocaldus yellowstonii • Ammonia-oxidizing bacteria (AOB): e.g N. eutropha, N. oligotropha, Nitrosospira multiformis • Heterotrophic nitrifiers: e.g Paracoccus pantotrophus • Anammox bacteria: e.g microbes of the order Planctomycetales
  54. 54. Nitrite oxidizers: Nitrite N Nitrate N • Nitrite-oxidizing bacteria (NOB): e.g Nitrobacter, Nitrococcus, Nirtospira
  55. 55. Conditions for Optimal Nitrification • Nitrification significantly consumes oxygen. oxidation of 1 mg liter-1 NH4+ to nitrate -------------- 3.6 mg liter-1 oxygen is required • Most strains of nitrifying bacteria are pH sensitive. optimal growth ------------ pH 7 to 8 • Reduction of carbonaceous BOD (cBOD) is a preliminary requirement: Best results ------------- when cBOD < 30 mg/L. • Temperature Min. 59 Degrees F. (15oC) ----------- 90 % Nitrification
  56. 56. • The hydraulic retention time (HRT) is the average retention time of wastewater in the reactor. “the ratio of liquid volume (V liquid) in the reactor and the flow rate (Q)” Depend on: Liquid Volume Flow Rate
  57. 57. Drawbacks of FBRs Traditional fixed-bed reactors can be easily blocked through: • excessive growth of microorganisms • crystalization of dissolved matter • solids which are fed in.
  58. 58. CONVENTIONAL ACTIVATED SLUDGE PROCESS
  59. 59. ACTIVATED SLUDGE sludge particles produced by the growth of microorganisms in aerated tanks as a part of the activated sludge process to treat wastewater
  60. 60. Activated Sludge Process The most common suspended growth process used for municipal wastewater treatment is the activated sludge process
  61. 61. In activated sludge process wastewater containing organic matter is aerated in an aeration basin in which micro-organisms metabolize the suspended and soluble organic matter. Part of organic matter is synthesized into new cells and part is oxidized to CO2 and water to derive energy. In activated sludge systems the new cells formed in the reaction are removed from the liquid stream in the form of a flocculent sludge in settling tanks. A part of this settled biomass, described as activated sludge is returned to the aeration tank and the remaining forms waste or excess sludge are discharged off as effluent.
  62. 62. ACTIVATED SLUDGE PLANT Activated sludge plant involves: • wastewater aeration in the presence of a microbial suspension • solid-liquid separation following aeration • discharge of clarified effluent • wasting of excess biomass • return of remaining biomass to the aeration tank
  63. 63. ACTIVATED SLUDGE PLANT
  64. 64. Weismann (1994) studied the nitrification in a conventional activated sludge system and found that it was relatively low for carbon removal and nitrification of sewage because carbon removal and nitrification occurred in the same reactor with an activated sludge system. This resulted in a population mixture of mainly heterotrophs and few autotrophs. In this kind of treatment system, it was not possible to enrich the autotrophic bacteria because the slower growing autotrophs were removed with the surplus sludge. It was necessary to separate the autotrophic from the heterotrophic biomass in order to increase the specific nitrification rate.
  65. 65. Suwa, et al. (1989), conducted a research on simultaneous organic carbon removal-nitrification by an activated sludge process with cross-flow filtration. Because of the recycle of sludge with cross-flow filtration, this process made the sludge retention time very long; simultaneous carbon removal-nitrification was achieved quite well under the loading rate of about 0.10 g BOD/g VSS/d. The efficiency of dissolved organic carbon removal was more than 95%, and nitrification was sufficient
  66. 66. Two Stage Activated Sludge System With Separate Carbonaceous Oxidation and Nitrification System
  67. 67. Activated sludge • Activated sludge is a process for treating sewage and industrial wastewaters using air and a biological floc composed of bacteria and protozoa.
  68. 68. Purpose • In a sewage (or industrial wastewater) treatment plant, the activated sludge process is a biological process that can be used for one or several of the following purposes: • oxidizing carbonaceous biological matter • oxidizing nitrogenous matter mainly ammonium and nitrogen in biological matter. • removing phosphates
  69. 69. Purpose • driving off entrained gases such as carbondioxide, ammonia, nitrogen, etc. • generating a biological floc that is easy to settle. • generating a liquor that is low in dissolved or suspended material.
  70. 70. The process • The process involves air or oxygen being introduced into a mixture of screened • and primary treated sewage or industrial wastewater (wastewater) combined with organisms to develop a biological floc which reduces the organic content of the sewage. • This material, which in healthy sludge is a brown floc, is largely composed of saprotrophic bacteria but also has an important protozoan flora mainly composed of amoebae and a range of other species.
  71. 71. The process • In poorly managed activated sludge, a range of filamentous bacteria can develop which produces a sludge that is difficult to settle and can result in the sludge blanket decanting over the weirs in the settlement tank to severely contaminate the final effluent quality. • This material is often described as sewage fungus but true fungal communities are relatively uncommon.
  72. 72. The process • The combination of wastewater and biological mass is commonly known as mixed liquor. • In all activated sludge plants, once the wastewater has received sufficient treatment, excess mixed liquor is discharged into settling tanks and the treated supernatant is run off to undergo further treatment before discharge.
  73. 73. The process • Part of the settled material, the sludge, is returned to the head of the aeration system to re-seed the new wastewater entering the tank. • This fraction of the floc is called return activated sludge (R.A.S.). Excess sludge is called surplus activated sludge (S.A.S.) or waste activated sludge (W.A.S).
  74. 74. • W.A.S is removed from the treatment process to keep the ratio of biomass to food supplied in the wastewater in balance, and is further treated by digestion, either under anaerobic or aerobic conditions prior to disposal.
  75. 75. Activated sludge control • The general method to do this is to monitor • sludge blanket level • SVI (Sludge Volume Index) • MCRT (Mean Cell Residence Time) • F/M (Food to Microorganism), as well as the of the activated sludge and the major
  76. 76. • Nutrients • DO (Dissolved oxygen), • Nitrogen • Phosphate • BOD (Biological oxygen demand) • COD (Chemical oxygen demand).
  77. 77. • In the reactor/aerator + clarifier system: • The sludge blanket is measured from the bottom of the clarifier to the level of settled solids in the clarifier's water column; this, in large plants, can be done up to three times a day. • The SVI is the volume of settled sludge in milliliters occupied by 1 gram of dry sludge solids after 30 minutes of settling in a 1000 milliliter graduated cylinder.
  78. 78. • The MCRT is the total mass (lbs) of mixed liquor suspended solids in the aerator and clarifier divided by the mass flow rate (lbs/day) of mixed liquor suspended solids leaving as WAS and final effluent • The F/M is the ratio of food fed to the microorganisms each day to the mass of microorganisms held under aeration.
  79. 79. Arrangement • The general arrangement of an activated sludge process for removing carbonaceous pollution includes the following items: • Aeration tank where air (or oxygen) is injected in the mixed liquor. • Settling tank (usually referred to as "final clarifier" or "secondary settling tank") to allow the biological flocs (the sludge blanket) to settle, thus separating the biological sludge from the clear treated water.
  80. 80. • Treatment of nitrogenous matter or phosphate involves additional steps where the mixed liquor is left in anoxic condition (meaning that there is no residual dissolved oxygen).
  81. 81. General arrangement of an activated sludge process
  82. 82. Two-stage nitrifying process • In a two-stage nitrifying process , the first stage removes most of the carbonaceous organic matter and the second stage oxidizes the ammonia. Typically, nitrification systems have lower F:M ratios than systems designed for CBOD removal alone.
  83. 83. Two-stage nitrifying process
  84. 84. Solids Handling control is a first step •Plant Return Flows are High in BOD and Ammonia •It inhibits Nitrification and Exceed Nitrification Capability of plant So we must , •Return plant flow Slowly • In Low Quantities •At Low Loading Times Operational Controls for Nitrification
  85. 85. Air Requirements must be controlled 1.5 lbs of O2 / lb of Biological oxygen demand 4.6 lbs of O2 / lb of Total kaldejhal Nitrogen Aerobic Reaction Time Must Be Long Enough……….> 5 hrs.
  86. 86. F:M (food to mass) Ratio Must Be Low Enough (< 0.25) BOD Removal is next step in Aeration Tank DO (dissolved oxygen) must be increased up to 3 - 5 mg/L
  87. 87. Nitrification VS D.O.NH3-NRemoval,% Dissolved Oxygen, mg/L 0 1 2 3 4 5 6 7 8 9 100 90 80 70 60 50 40
  88. 88. Effluent BOD Vs % NH3-N Removal Effluent BOD, mg/L 0 10 20 30 40 50 60 70 80 NH4-NRemoval,% 100 90 80 70 60 50 40 30 20 10 0
  89. 89. Temperature Substrate concentration Dissolved oxygen (DO) pH Toxic & inhibitory substance Factors Affecting Nitrification
  90. 90. NitrifierGrowthRate 0 5 10 15 20 25 30 35 40 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Temperature, oC Effect of Temperature on Nitrification Lower the Temperature, Slower will be the growth rate of Nitrifier
  91. 91. 90 % Nitrification requires Minimum of 59 Degrees F. (15oC) Below 50 Degrees F. (10 oC) Maximum of 50 % Nitrification can be expected only Ideal Temperature is between 30oC and 35oC (86oF and 95oF)
  92. 92. (Ammonium bicarbonate)NH4HCO3 + O2 HNO3 (nitric acid) + H2O + CO2 7 mg Alkalinity is Destroyed Per mg NH3-N Oxidiation Chemicals Added For Phosphorus Removal Also Destroy Alkalinity Adequate Alkalinity is required Effluent Above 50 mg/L Influent Above 150 mg/L 5.3 - 13.5 lbs of Alkalinity is added per lb Fe 6.0 - 9.0 lbs of Alkalinity id added per lb Al pH will decrease If Not Enough Alkalinity is Present Nitrifiers are pH Sensitive Optimum pH for Nitrosomonas 7.5 & 8.5 for Nitrobacter Effect of alkalinity on Nitrification
  93. 93. pH VS Nitrification Rate at 68 oF pH 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 100 90 80 70 60 50 40 30 20 10 0 %ofMaxNitrificationRate
  94. 94. Cyanide, thiourea, phenol and heavy metal, nitrous acid and free ammonia can inhibit nitrifying bacteria. Nitrification occur only when DO level is 1.0 mg/L or more.

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