Department of Civil Environmental Engineering

2. Life � Solar radiation: Photo-synthetic autotrophs � Organics: Heterotrophs � Inorganics: Chemoautotrophs

3. Photo-Synthetic Autotrophs � Derive energy from sunlight � H & O ? H O; C ? CO N, P, S, etc. ? dissolved salts Not readily soluble Eutrophic (life-giving) substances � N ?NH & NO ; from natural and manmade sources � P ?PO ; from human body waste, food waste, various household detergents

4. � Form complex high energy organics (H, O, C) and produce O2. � Algae; Oxidation (facultative) pond

5. Heterotrophs � Derive energy by oxidizing organics � Use high energy organics to form more complex biomass constituents including proteins � Energy - Cell mass production - Free energy generation - Heat loss When organic energy reduces to zero, heterotrophic life ceases. � Floc formers in activated sludge

6. Chemotrophs � Derive energy by oxidizing inorganics � Nitrifying bacteria (obligate aerobes) � Denitrifiers Heterotrophs can be forced to utilize NO3- & NO2-.

7. Phosphorus Removing Mechanism

9. � Aerobic respiration � O2 present � Electron acceptor: O2

10. � Anaerobic respiration � NO and NO present � Electron acceptor: NO and NO

11. � Fermentation � No O , NO , NO , or SO present � Electron acceptor: endogenously generated by the microorganism

12. COD/VSS [�COD(bac)/�Xa], fcv �COD(sol) = �COD(bacteria) + �O (utilized) �O2 = (1 - YCOD) � �COD(sol) � YCOD = �COD(bacteria)/�COD(sol) = fcv � Yh = (1 - fcv�Yh) � �COD(sol)

13. Empirical Stoichiometric Formulation

14. Subdivision of Influent COD

15. Biodegradable & Unbiodegradable Fractions 1. Measure carbonaceous oxygen demand (Oc), Yh, and bh from a lab-scale exp. 2. By trial and error, find Sbi value that balances the equation below. M(Oc) = M(Osynthesis) + M(Oendogenous decay) = (1-fcvYh)M(Sbi) + fcv(1-f)bhM(Xa) (mg O/d) M(Sbi) = Q � Sbi; M(Xa) = Q � Xa

16. Graphical Determination of Carbonaceous Oxygen Demand

19. Determination of Readily Biodegradable Soluble COD (Sbsi) Consists of simple organic molecules such as volatile fatty acids (VFAs) and low molecular weight carbohydrates that can pass through the cell membrane and be metabolized within minutes. Sbsi = Total truly sol. CODinf - Non-readily sol. CODinf Total truly sol. CODinf is determined by flocculating with Zn(OH)2 at pH 10.5 and filtering with a 0.45 �m filter. Non-readily sol. CODinf is determined by performing the above test with the effluent of a 24 hr fill-and-draw activated sludge system (MCRT > 3 days).

20. Flocculation Method Add 1 mL of a 100 g/L zinc sulfate solution to a 100 mL wastewater sample and mix vigorously with a magnetic stirrer for 1 min. Adjust the pH to approx. 10.5 with 6 M sodium hydroxide solution. Settle quiescently for a few minutes. Withdraw clear supernatant (20 ~ 30 mL) with a pipette and pass through a 0.45 �m membrane filter. Measure COD on the filtrate.

21. Influent Wastewater COD Fractionsfor settled and unsettled sewage Sewage Sewage fraction Unsettled Settled Soluble unbiodegradable fraction, fus 0.05 0.08 Particulate unbiodegradable fraction, fup 0.13 0.04 MLVSS/MLSS ratio (fi) 0.75 0.83

24. Effects of Waste Characteristics on Design 1. Influent COD & Q (mean daily flow) Q affects the design of the secondary clarifier.

25. Effects of Waste Characteristics on Design 2. Influent TKN, �nmT, and temp. Sludge age will be controlled by the level of energy removal. e.g. Carbonaceous removal : ~ 3 days of sludge age Nitrogenous removal: depends on �nmT Nitrifiers are temperature sensitive. e.g. A nitrification-denitrification plant, �nm = 0.3 At T = 20�C, 4 days of sludge age At T = 12�C, 15 - 20 days of sludge age

26. Effects of Waste Characteristics on Design 3. Readily & slowly biodegradable COD COD for denitrification: Sbsi + Sbpi + SBiomass lysis 4. Influent TP/COD concentration ratio (Pti/Sti) TP/CODinf � 0.017~0.02 mg P/mg CODinf If TP/CODinf < 0.017~0.02; Effl. P� 0.5 mg P/L possible If TP/CODinf > 0.017~0.02; Chemical precipitation necessary

28. Effects of Waste Characteristics on Design

29. Effects of Waste Characteristics on Design � TKN/COD < 0.09: Bardenpho process � TKN/COD > 0.10: Modified Ludzack-Ettinger process (MLE) � TKN/COD < 0.07 ~ 0.08: A/O, A2/O, Phoredox process (modified Bardenpho) � TKN/COD < 0.12 ~ 0.14: UCT process � TKN/COD < 0.11: Modified UCT process

30. Reactor Types

31. Sludge Age, Rs

32. Short Sludge Ages (1 ~ 5 days) � COD removal only � BOD/COD reduction: 75 ~ 90% � Predatory activity, which causes turbidity and high effluent COD, is relatively low. � No nitrification

33. Intermediate Sludge Ages (10 ~ 15 days) � Effluent COD and ammonia are no longer an important design factor. Sludge age is determined by the requirement for nitrification. Nitrification causes a significant pH reduction, often as low as 5. Once denitrification is considered, sludge ages longer than 10 ~ 15 days are required. Oxygen demand per kg COD is doubled and the process volume is 3 ~ 4 times larger.

34. Intermediate Sludge Ages (10 ~ 15 days) � Denitrification in the secondary clarifier takes place, causing sludge flotation by nitrogen gas bubbles. The secondary clarifier may not serve the dual purpose of solid-liquid separation and thickening. Sludge residence time must be minimized by increasing the underflow recycle ratio to 1 to 2:1.

35. Long Sludge Ages (20 days or more) � Called "extended aeration plants" Compared to intermediate sludge age plants, the total oxygen demand is about equivalent and the process volume is 50 ~ 60% larger. � When treating low alkalinity wastewater, the problem of low pH is expected. Problem of rising sludge is expected. A low COD effluent but with high nitrate and phosphate is expected. An anoxic zone will prevent low pH and reduce nitrate concentration.

36. Long Sludge Ages (20 days or more) � Nitrification/denitrification occur. Effluent nitrate conc. is reduced. Total oxygen demand can be reduced to 15 ~ 25% compared with nitrification process. Problem of rising sludge is eliminated. Problem of low pH effluent is eliminated.

37. Long Sludge Ages (20 days or more) � Nitrification/denitrification and P removal occur. Aeration (oxygen) control is a problem under cyclic load and flow conditions. Load and flow equalization may be required. When the sludge becomes anaerobic or is anaerobically digested, P will be released from the sludge mass to the bulk liquid.

38. Nitrification

40. Nitrosomonas Kinetics

43. Minimum Sludge Age for Nitrification

44. Factors Influencing Nitrification 1. Influent source �nm: specific to the source of the waste and even different from batch to batch from the same source; should be classified as a wastewatecharacteristic. Ranges: 0.30 to 0.65 1/day The test is performed in a single completely mixed reactor at about 6 to 10 day sludge age with alternating cycles of anoxic and aerobic periods of 2 to 3 hours each.

45. Factors Influencing Nitrification 2. Temperature For every 6�C drop, the value will halve. � Design for nitrification plant should be based on the minimum expected temperature.

46. Factors Influencing Nitrification 3. pH Optimal nitrification pH: 7.2 < pH < 8.5 For 7.2 < pH < 8.5 For 5 < pH < 7.2

48. Factors Influencing Nitrification 4. Alkalinity (as CaCO3) 2 moles of hydrogen ion � 1 mole of alkalinity If alkalinity < 40 mg/L as CaCO3; then dangerous. Ex. alk. = 200 mg/L as CaCO3; nitrate production = 24 mg N/L. Expected alk. = 200 - 7.14�24 = 29 mg/L as CaCO3.

50. Factors Influencing Nitrification 5. Unaerated zones Assumptions: nitrifiers grow only in the aerobic zone. Endogenous decay occurs under both aerobic and anoxic conditions. The nitrifier concentrations in the aerated and unaerated zones are equal.

51. Factors Influencing Nitrification 5. Unaerated zones - cont. Minimum sludge age Minimum aerobic sludge mass fraction Maximum allowable unaerated mass fraction

52. Factors Influencing Nitrification 6. Dissolved oxygen concentration O = oxygen conc. in bulk liquid (mg O/L) Ko = half saturation const. (mg O/L) �nmo = maximum specific growth rate (1/day) �no = specific growth rate (1/day) Ko: 0.3 ~ 2 mg O/L Minimum oxygen conc.: 2 mg O/L

53. Factors Influencing Nitrification 7. Stimulation of Nitrifying Bacteria

54. Factors Influencing Nitrification

55. Factors Influencing Nitrification 9. Cyclic flow and loading A conservative estimate of �nm is essential for a safe design. Otherwise, even with a safety factor, nitrate concentration in the effluent will fluctuate.

56. Specific Growth Rate

57. Biological Denitrification Nitrate Reduction in biological systems Assimilation: Nitrate to ammonia Dissimilation or denitrification: NO3- ??NO2- ??NO ??N2O ??N2 Bacteria capable of denitrification are both heterotrophic and autotrophic. Achromobacter, Acinetobacter, Agrobacterium, Alcaligenes, Arthrobacter, Bacillus, Chromobacterium, Corynebacterium, Flavobacterium, Hypomicrobium, Moraxella, Neisseria, Paracoccus, Propionibacterium, Pseudomonas, Rhizobium, Rhodopseudomonas, Spirillum, and Vibrio Thiosphaera pantopropha (heterotroph) is known to nitrify and denitrify simultaneously under aerobic conditions using acetate as a carbon source.

58. Biological Denitrification When nitrate serves as the electron acceptor, the equivalent mass of oxygen (as O) is: 1 mg NO3-N ? 2.86 mg O as O Thus, for nitrification, 4.57 mg O/mg N are required, but in denitrification, 2.86 mg O/mg N can be recovered, i.e., with denitrification, 2.86/4.57�100 = 63% of the oxygen demand for nitrification can be recovered.

60. Requirement for Denitrification 1. Presence of nitrate (or nitrite) 2. Absence of dissolved oxygen When DO � 0 mg/L, 100% denitrification When DO � 0.2 mg/L, no significant denitrification. 3. A facultative bacterial mass 4. Presence of a suitable electron donor (energy source) Addition of readily biodegradable COD increases the denitrification potential.

61. Denitrification Reaction Nn = nitrate conc. (mg N/L) K = specific denitrification const. (mg N/mg VSS/day)

63. Primary Anoxic Reactor �Nnps = �Nn1s + �Nn2s = K1Xat1 (a + 1) + K2XaRap (a + 1) = K1Xat1 (a + 1) + K2XaRnp t1 = duration of the first denitrification phase.

64. Primary Anoxic Reactor �Nn1s = ?Sbi ? = 0.028 mg N/mg biodegradable COD = fbs (1 - fcv Yh)/2.86

65. Secondary Anoxic Reactor

66. Nitrate Removal and Substrate Utilization For the utilization of 1 mg COD under aerobic conditions, an amount of 0.33 mg oxygen (1 - fcvYh = 1 - 1.48 � 0.45) is required. As the oxygen equivalent of nitrate is 2.86 mg O/mg N, the nitrate consumption per mg COD utilized is (1 - fcvYh)/2.86 = 0.116 mg N/mg COD or conversely 8.6 mg COD are required to reduce 1 mg nitrate nitrogen. The first phase of denitrification rate is associated with the utilization of the readily biodegradable COD of the influent.

67. Alkalinity Change � Biological denitrification is accompanied by an increase in alkalinity. 3.57 mg/L as CaCO3 alkalinity recovered per 1 mg NO3-N denitrified During nitrification, 7.14 mg/L as CaCO3 alkalinity is consumed per 1 mg NH3-N nitrified. Hence, for low alkalinity waste, denitrification is strongly recommended to prevent the pH drop.

68. Biological Phosphorus Removal (BPR)

69. Phosphate Release and Uptake -Secondary Release

70. Biological Phosphorus Removal (BPR) Phosphorus Removal Mechanism Entirely by disposal of sludge containing larger portions of phosphorus in the biomass than conventional activated sludge

71. Phosphate Release and Uptake -Secondary Release: Design Implications For fairly fresh, weak sewage, any effort at acid fermentation in the anaerobic basin (by increasing HRT in the anaerobic zone) is counterproductive. For strong, partially fermented sewage, a longer anaerobic retention time may be useful. With prefermentation, the designer can make sure that conditions will be optimal for the growth of acinetobacter even with weak wastewater and low temperatures.

72. Phosphate Release and Uptake -Secondary Release: Design Implications Without prefermentation, the five-stage Bardenpho performed reasonably, but when the plant was switched to the UCT configuration, phosphate removal was lost until the size of the anaerobic basin configuration was doubled (Daspoort, Pretoria) - longer anaerobic mass fraction increased the VFA production. Phosphate removal was improved by switching to the UCT mode even though nitrate were not present in the RAS underflow (Westbank, British Columbia) - reducing anaerobic mass fraction improved the plant performance.

73. Importance of Nitrate for P Removal Nitrates constitute the single most important factor that must be controlled to ensure good performance by BNR plants. Exception: Some wastes containing sufficientn the RAS. In situations whether most wastewater is pumped to the plant and the temperatures are favorable, P removal will take place without a serious attempt at reducing nitrates. When high percentage removal of both N and P is required, the plant should be biased towards nitrogen removal, since augmenting P removal with chemicals is much less costly and easier to control.

74. Importance of Nitrate for P Removal VFAs as well as other easily degradable materials are responsible for the first high rate of denitrification. However, the idea is to reserve the SCVFA for the BioP organisms. If the available carbon is not sufficientan be augmented by prefermentation. The major portion of the BioP organisms removes little or no nitrates. Thus, the food they remove preferentially is not available for denitrification. Although some of the VFAs needed for the rapid denitrification in the anoxic zone has been sequestered by the BioP organisms, the stored COD more than makes up for the shortfall and allows a high percentage denitrification.

75. Biological Phosphorus Removal (BPR) With BPR processes alone, an effluent total P limit of 1.0 to 2.0 mg/L can be achieved if the practice of anaerobic digester supernatant recycle were terminated or if digester supernatant were treated chemically to remove released phosphorus prior to recycle to the biological process. To achieve an effluent total P limit of 1.0 mg/L, effluent filtration or chemical precipitation will be required. To consistently achieve an effluent total P limit of 0.3, all the BPR processes require final effluent filtration.

76. Biological Phosphorus Removal (BPR) BPR facilities should be designed to biologically reduce the phosphorus content of the wastewater to a practical minimum and the residual phosphorus should be removed chemically to the prescribed effluent limit. Chemical back-up to the BPR process is recommended. More attention needs to be devoted to sludge management practices.

77. Biological Phosphorus Removal (BPR) Flow and load equalization to the BPR process Exclusion of recycle streams containing high phosphate (soluble and/or particulate) Compartmentalization of the BPR basins Flexibility in use of BPR basin volumes between anaerobic, anoxic, and aerobic environments Ability to provide a source of readily metabolizable soluble carbon in the influent to the BPR process Maintenance of an oxygen-free and nitrate-free environment in the anaerobic basin

78. Biological Phosphorus Removal (BPR) The minimum readily biodegradable COD concentration in the anaerobic reactor (Sbsa) to simulate phosphorus release in the reactor is about 25 mg COD/L. The degree of P release appears to increase as Sbsa increases above 25 mg COD/L, i.e., P release increases as (Sbsa-25) increases. Excess phosphorus uptake is obtained only when phosphorus release takes place, and tends to increase with (Sbsa-25).

79. Determination of Sbsa The Phoredox Process

80. Biological Phosphorus Removal (BPR) 1. Excess P removal is obtained only when Sbsa > 25 mg COD/L. 2. As Sbsa increases above 25 mg COD/L, so the P removal increases. 3. The longer the actual anaerobic retention time (Ran), the higher the P removal. 4. The larger the mass of sludge recycled through the anaerobic reactor per day expressed as a fraction of the mass of sludge in the process, n, the higher the P removal.

81. Biological Phosphorus Removal (BPR) When any one of the factors (Sbsa-25), Ran, or n is zero, excess P removal will be zero. Excess P removal propensity factor, Pf, can be expressed as follows: Pf = (Sbsa - 25) � Ran � n The P removal due to excess uptake in the sludge, Ps, is: Ps = f(Pf)

82. Biological Phosphorus Removal (BPR) Ran � n = fxa (anaerobic mass fraction). Then, Pf = (Sbsa - 25) � fxa when Sbsa > 25 Pf = 0.0 when Sbsa � 25 Semi-empirical model for Ps (mg P/L):

83. ?vs Pf Observed in BPR Processes

84. Biological Phosphorus Removal (BPR) Influent COD conc.: 250 - 800 mg COD/L Readily biodegradable COD: 70 - 220 mg COD/L i.e., fraction fts : 0.12 - 0.27 TKN/COD ratio: 0.09 - 0.14 Sludge age: 13 - 25 days Temperature: 12 - 20�C The use of this model must be limited strictly to within the ranges of process parameters and wastewater characteristics listed herein.

85. P Removal per mg COD Load

86. Pf, Sbsa, and ?vs Nitrate Concentration

87. Case HistoriesLargo WWTP, Largo, Fl Facility Description Preliminary, primary, and secondary treatment plus effluent filtration and disinfection 15 MGD; < 10 days of sludge age; > 20�C The A2/O process to remove both N and P HRT: 0.8 hr in the anaerobic zone, 0.5 hr in the anoxic zone, and 2.9 hrs in the aerobic zone Effluent Limits Effluent TBOD5 and TSS: 5 mg/L N limitations: Total N - Annual avg. 8 mg/L; Monthly avg. 12 mg/L; Weekly avg. 18 mg/L Effluent ammonia-nitrogen Monthly avg. 2 mg/L; Weekly avg. 3 mg/L

88. Largo WWTP, Largo, Fl Wastewater Characteristics A typical medium strength Operating Results Avg. plant Q: 9.9 MGD; MLSS: < 3000 mg/L Avg. TBOD5 and TSS: 5 and 4 mg/L Avg. monthly TN: 7.7 mg/L RAS: 0.5 Q; Recycle from A to AX: 1 ~ 2 Q Provided partial nitrogen removal

89. Palmetto WWTP, Palmetto, Fl

90. Palmetto WWTP, Palmetto, Fl Effluent Limits TBOD5: 5 mg/L TSS: 5 mg/L TN: 3 mg/L TP: 1 mg/L Wastewater Characteristics A typical medium strength

91. Palmetto WWTP, Palmetto, Fl Operating Results During the operation, the plant was loaded at and above its design hydraulic capacity (1.4 MGD), but it was underloaded with respect to organic and nutrient loadings. Q: 0.74 ~ 2.44 MGD; TBOD5: 54% of design Sludge age: 14 (summer) to 20 (winter) days Avg. MLSS: 4090 mg/L; design MLSS: 3500 mg/L Met its effluent permit limitations Summary A successfully operating Bardenpho nutrient removal plant The need to provide an adequate sludge age capacity for extensive N removal.

92. Guidelines for Biological Nutrient Removal (BNR) Process Selection Nitrogen Removal Four Stage Bardenpho Process Modified Ludzack-Ettinger (MLE) Process Phosphorus Removal Only A/O Process Nitrogen and Phosphorus Removal Five Stage Bardenpho (Phoredox) Process University of Cape Town (UCT) Process Modified UCT Process Virginia Initiate Process (VIP)

93. Process Selection Based on TKN/COD ratio (Initial Screening) Nitrogen Removal TKN/COD < 0.09: Bardenpho process TKN/COD > 0.10: MLE process Nitrogen and/or Phosphorus Removal TKN/COD < 0.07 ~ 0.08: A/O, A2/O, Phoredox process (modified Bardenpho) TKN/COD < 0.12 ~ 0.14: UCT process TKN/COD < 0.11: Modified UCT process

94. BPR process requirements for variouseffluent total phosphorus limits(CANVIRO Consultants Ltd, 1986) Eff. TP, mg/L Phoredox UCT A/O Phostrip 1.0 - 2.0 BPR BPR BPR BPR 1.0 BPR + filt. BPR + filt. BPR + filt. BPR or or or BPR + chem. BPR + chem. BPR + chem. 0.3 BPR + filt. BPR + filt. BPR + filt. BPR + filt. + chem. + chem. + chem.

95. Biological Nutrient Removal (BNR)Process Comparison Nutrient removal Sludge Effluent capability disposal Chem. filtration Oper. Oper. Cost Process P N impact req. req. flex. reliability impact Phostrip Best Little M M Least G G M Bardenpho Least B L L Most L M H Oxidation ditch NA G L L NA M M L A2/O M M L L Most L L L UCT G M L L Most M M M Chemical treat. Best Little H H Least B B HH

96. Item Conventional ENR Total P (mg P/L) Influent 6 6 Equiv. P-conc. in waste sludge 1.5 4.5 Effluent (by difference) 4.5 1.5 Removal efficiency (%) 25 75 Alum required (lb/mgal) 584 83 Cost of alum ($/mgal) 39.4 5.6 Nitrogen (mg P/L) Influent TKN 30.0 30.0 Equiv. N-conc. in waste sludge 8.9 8.9 Sol. nonbiodeg. TKN 1.5 1.5 Nitrate before denitrification 22.6 7.9 Denitrified 0 14.7 Effluent nitrate (by difference) 22.6 7.9 Effluent total nitrogen 24.1 9.4 Removal efficiency (%) 20 69

97. Process Oxygen and Alkalinity Requirement Item Conventional ENR Oxygen demand (mg/L) Carbonaceous 140 140 Nitrogenous 104 104 Credit for denitrification 0 42 Net (by difference) 244 202 Savings (%) 0 17 Alkalinity (mg/L as CaCO3) Consumed by nitrification 163 163 Produced by denitrification 0 53 Net consumption (by difference) 163 110 Savings (%) 0 32

98. Process Selection Based on CODinf/P ratio (Initial Screening) If TCODinf/TP > 50 mg CODinf/mg P; Effl. sol. P � 0.5 mg P/L is possible with biological phosphorus removal processes If 40 � TCODinf/TP � 50 mg CODinf/mg P; Effl. sol. P � 1 mg P/L is possible with biological phosphorus removal processes If TCODinf/TP < 40 mg CODinf/mg P; Prefermentation or effluent polishing by chemical precipitation is necessary

99. Phosphorus vs COD Limitation If phosphorus is limiting, the available organics will not be completely removed in the anaerobic stage and soluble organics will enter the aerobic stage. Thus, the aerobic zone size should be enlarged. If COD is limiting, the P removal will be limited and the desired effluent P concentration may not be achievable without prefermentation or supplemental chemical addition. If biodeg. COD:TP ratio is considerably higher than 40:1 whereas the BOD5:TP ratio is considerably lower than 20:1, then the wastewater has not undergone substantial fermentation and thus make the anaerobic zone larger.

100. Aeration Requirements In general, oxygen requirements are reduced by BPR processes. It is recommended that the theoretical require-ments be reduced by 10% for design purposes. During aeration with draft tubes, there exists no or very low DO in the mixed liquor. This results in denitrification in the aeration basin varying from 30 to 100%. Assume 10 to 20% of the total nitrogen nitrified will be lost through simultaneous denitrification in the diffused-air aeration basin.

101. Modified Ludzack-Ettinger Process (MLE) � Nitrogen removal only. First biological nitrification-denitrification process. Complete denitrification is not possible.

102. Bardenpho Process Nitrogen removal only. P removal incidental. Introduced a flash aeration basin between the secondary anoxic reactor and the clarifier to strip N2. Maintain thin sludge blanket to prevent sludge flotation due to denitrification of residual nitrate.

103. Modified Bardenpho (Phoredox) Process Nitrogen/phosphorus removal. Maintain thin sludge blanket to prevent sludge flotation due to denitrification of residual nitrate.

104. The Phoredox Process An anaerobic fraction (fxa) of the total unaerated sludge mass fraction (fxt) is set aside to establish the prerequisites for excess phosphorus removal. If no nitrate is to be recycled to the anaerobic reactor, complete denitrification must be achieved in the anoxic sludge mass fraction (fxdt = fxt-fxa). Complete denitrification is achieved only when the TKN/COD ratio < 0.085. As a safety, the ratio should not exceed 0.07 to 0.08 at 14�C for sludge ages 20 to 30 days. This restricts application of this process for municipal waste-water treatment having higher TKN/COD ratios.

105. Modified Bardenpho (Phoredox) Process Five-stage Bardenpho basin hydraulic retention times (hrs) Basin Typical range Palmetto, Fl. Kelowna, B.C. Anaerobic 1 - 2 1.0 2.9 First anoxic 2 - 4 2.7 2.9 First aerobic 3 - 8 4.7 8.6 Second anoxic 2 - 4 2.2 3.8 Second aerobic 0.5 - 1 1.0 1.9 Total 8.5 - 19 11.6 20.1

106. Three Stage Phoredox Process Modified for partial denitrification. Basically identical to A2/O process. For A2/O, basins are tightly compartmentalized.

107. No nitrification. Basically identical to A/O process. Greater degree of compartmentalization of the basins in A/O system. A/O process uses high purity oxygen while this process uses air for aeration.

108. A/O Design Considerations Size of the anaerobic zone, prefermentation, sludge age; subdivision of anaerobic zone, mixing requirements Incorporate sufficient flexibility for the operator to adjust the system to varying conditions. Prevent significant entrainment of DO into the anaerobic mixed liquor phosphorus during clarification and recycle of phosphorus from sludge processing.

109. A/O and A2/O Processes Typical A/O and A2/O design and operating parameters Variable Units Range Influent retention time Anaerobic section hrs 0.5 - 1.0 Anoxic section hrs 0.5 - 1.0 Aerobic section Non-nitrifying (A/O) hrs 1.8 - 2.5 Nitrifying (A2/O) hrs 3.5 - 6.0 F/M ratio kg BOD5/kg MLVSS�day 0.15 - 0.7 Soluble BOD5/soluble P (influent) - � 10 Mixed liquor suspended solids mg/L 2000 - 4000 Temperature �C 5 - 30 RAS recycle rate % of influent flow 25 - 75 Internal mixed liquor recycle rate % of influent flow 50 - 250 Basin configuration type - Staged system Number of stages: Anaerobic/anoxic/aerobic - 3/3/4

110. Virginia Initiate Plant (VIP) Process Similar to the UCT process. Multiple complete mix cells are used for the anaerobic, anoxic and aerobic treatment zones to increase the phosphorus uptake rate by virtue of a higher concen-tration of residual organics in the first aerobic cell. The VIP process is designed for a total sludge age of 5 to 10 days while the UCT process is generally designed for an sludge age of 13 to 25 days.

111. University of Cape Town (UCT) Process RAS passes through "A" basin prior to entering "AN" basin for residual NO3- removal; thus, provides an additional barrier to the entry of NO3- into the anaerobic basin. Full-scale confirmation of design and performance data are presently lacking.

112. The UCT Process For TKN/COD ratios > 0.14, nitrate will be present in the primary anoxic reactor and a discharge of nitrate to the anaerobic reactor cannot be avoided leading to a decline in excess P removal. As a safety, the upper limit is 0.12 to 0.14. This limit is above that for most settled and raw municipal wastewaters. Problems associated with the UCT process 1. Process control 2. Sludge settleability

113. University of Cape Town (UCT) Process The a-recycle must be carefully controlled to just underload the primary anoxic basin with nitrate to avoid a nitrate discharge to the anaerobic basin. Under full-scale operation such careful control of a-recycle is not possible due to uncertainty in the TKN/COD ratio. As the TKN/COD ratio increases, the a-recycle ratio needs to be decreased to avoid a nitrate discharge to the anaerobic basin, which in turn causes an increase in the actual anoxic retention time. For inf. COD > 500 mg/L and TKN/COD ratio > 0.11, the actual anoxic retention time exceeds 1 hr, causing the decline of sludge settleability.

114. Modified UCT Process Avoids careful control of a-recycle. Limit the anoxic retention time to 1 hr to improve sludge settleability.

115. The Modified UCT Process Process control: The UCT process requires a careful control of a-recyle to the primary anoxic reactor to avoid a nitrate discharge to the anaerobic reactor, which is impossible due to uncertainty in the TKN/COD ratio, particularly under cyclic flow and load conditions. Sludge settleability: When the actual retention time exceeded 1 hr, the sludge settleability declined. To preserve good settleability of the sludge, the actual anoxic retention time should be limited at 1 hr.

116. Schematic Process Configurationfor Optional Operations

117. Retrofit of Existing Plants Aeration basin size and configuration Clarifier capacity Aeration requirements Type of aeration system Sludge processing units Operator skills

118. Aeration Basin Size and Configuration No need to increase the size because the removal of substrate in the anaerobic zone is more rapid than in the aerobic zone of equal size. A plug flow basin is the easiest type to retrofit.

119. Clarifier Modification Usuallythan centerfeed clarifiers because the flow is usually up through the sludge blanket. Some phosphorus release typically occurs in the clarifier sludge blanket of a BPR plant but in a properly operated centerfeed clarifier the entire sludge blanket plus the released phosphorus is drawn off the bottom of the clarifier and recycled to the anaerobic zone.

120. Aeration Requirements and Type of Aeration System The aeration equipment is usually removed from any zone that will permanently become a part of the anaerobic zone. There is no need to add additional aeration equipment because the processes in the anaerobic zone reduce the oxygen transfer requirements by 10 to 20%. The primary concern should be the protection of the anaerobic zone from the recycle of too much dissolved oxygen.

121. Sludge Processing Units The inclusion of BNR results in a 5 to 15% reduction in WAS while the inclusion of BPR will increase the WAS production slightly. The sludge processing units are of primary concern. The recycle of any soluble P changes the COD:P ratio entering the activated sludge process. The use of anaerobic digesters, gravity thickeners for waste activated sludge (WAS), and the recycle of the WAS for settling with the primary sludge in the primary clarifier are detrimental if not properly managed.

122. Sludge Treatment Alternatives for BNR WWTPs

123. Sludge Processing Units - continued Sludge dewatering Separate the thickening of primary sludge and WAS. Flotation thickening is ideal. After thickening, the sludge may be further dewatered by belt press with the addition of polymers. Note that some polymers inhibit nitrification. After thickening or dewatering the sludge may be treated by: composting, digestion, landfill, incineration, heat treatmenttreatment

124. Sludge Processing Units - continued Composting Primary sludge can be dewatered to 22% solids and WAS to 16%. No phosphates will be released. Digestion (aerobic and anaerobic) This will lead to the release of phosphates from the microbial cells. In some instances, phosphates may be precipitated during anaerobic digestion. If the liquid is to be returned

125. Sludge Processing Units - continued Landfill Phosphates will be bound by the heavy metals in the leachate. Usually no problem. Incineration Separate the primary and secondary sludges. No problem. Heat treatment It may return unwanted (nondegradable) compounds

126. Operator Skills Greater operatort the necessary skills are easily learned and applied. A retraining program for the operators should be part of any retrofit project.

127. Case Histories: The York River, Virginia, Wastewater Treatment Plant Simultaneousf 7.4 hrs; primary sludge gravity thickeners, secondary sludge dissolveds, and belt filter presses; no supernatant recycle from the anaerobic digesters but the recycle of the filtrate from the belt presses and the supernatants from the thickeners. The projected retrofit cost is $2 million ($133,000 per 1 MGD).

128. Case Histories: The York River, Virginia, Wastewater Treatment Plant

129. Limitations There were low concentrations of organics in the raw wastewater compared to TKN and P. The organic strength of the wastewater was reduced by preaeration and primary settling before entering the biological process Phosphorus was recycled back to the headworks from the two sludge thickening processes and from anaerobic digestion. BOD5:P ratio - raw = 18:1 to 27:1, combined flow = 15:1, primary effluent = 12.5:1.

130. Process Start-Up

131. Sludge Production F:M = 0.47 (BOD5) = 0.89 (COD) Sludge production = 0.48 kg TSS/kg BOD5 removed (MCRT = 3.2 ~ 7.9 days) A nutrient removal pilot plant: 0.77 kg TSS/kg BOD5 removed Sludge production = 0.26 kg TSS/kg BOD5 removed (MCRT = 10 ~ 14 days) 22 mg/L of BOD5 consumed for 1 mg/L of P removed by BPR for anaerobic mass fraction of 33%.