Introduction to Oxygenation and Aeration Systems

Transcription

1 Introduction to Oxygenation and Aeration Systems John Little Civil and Environmental Engineering Virginia Tech, Blacksburg, Virginia, USA

2 Acknowledgments Kevin Bierlein, Virginia Tech (PhD) Lee Bryant, Virginia Tech (PhD) and Duke/Eawag (Postdoc) Paul Gantzer, Virginia Tech (MS and PhD) Dan McGinnis, Virginia Tech (MS and PhD) and Eawag (Postdoc) Vickie Singleton (Burris), Virginia Tech (MS and PhD) Johny Wüest, Eawag and EPFL Francisco Rueda, University of Granada Bob Benninger, Western Virginia Water Authority Mark Mobley, Mobley Engineering National Science Foundation CBET CBET DGE (IGERT) CBET Western Virginia Water Authority Tennessee Valley Authority City of Norfolk, Virginia Canton Aargau, Switzerland

3 Presentation Outline Why do we need to add oxygen? Primary oxygenation/aeration systems Oxygen transfer theory Models to predict system performance Sediment oxygen demand Oxidizing iron and manganese Coupled bubble-plume/reservoir model

4 Stratification Oxygen Depletion Hypolimnetic oxygenation to replenish oxygen Figures from Baudirektion Kanton Zürich

5 Why do we need to add oxygen? Hydropower reservoirs Water-storage reservoirs used for drinking water Cold-water fisheries Eutrophication of surface waters

6 Hydropower Reservoirs

7 Drinking Water Treatment Depletion of dissolved oxygen Withdraw water from anoxic hypolimnion Iron, manganese, and hydrogen sulfide from sediment (color, odor) Increased oxidant demand (more chlorine, more DBPs, more corrosion) Increased phosphorus (algal blooms, more coagulant, shorter filter runs)

8 Fish (hypoxia <2.8 mg O 2 /L)

9 Eutrophication - Swan Estuary Perth, Western Australia

10 Salt Wedge Oxygen Depletion

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13 Can we solve the problem by reducing nutrient load? Baudirektion Kanton Zürich

14 Baudirektion Kanton Zürich

15 Baudirektion Kanton Zürich

16 Baudirektion Kanton Zürich

17 Oxygenation and Aeration Systems Four main systems Speece Cone (oxygen) side-stream supersaturation (oxygen) airlift aerator (air) bubble plume (air or oxygen)

18 Courtesy of Rod Jung Speece Cone

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20 Side-Stream Supersaturation Courtesy of Mark Mobley

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22 Courtesy of Bob Kortmann Airlift Aerator

23 Courtesy of Bob Kortmann

24 Courtesy of Mark Mobley Bubble Plume

25 Selected Installations Reservoir Type Application Capacity/Cost Camanche Lake Prince Richard B. Russell Upper San Leandro Spring Hollow Carvin s Cove Speece Cone (1 unit) Airlift Aerators (25 units) Bubble Plume ( m) Bubble Plume (2 730 m) Bubble Plume (1 400 m) Bubble Plume (2 600 m) Hydropower Water supply Hydropower Water supply Water supply Water supply Liquid oxygen costs ~ $100/ton 9 tons O 2 /day $1.8M 10 tons O 2 /day $2.8M 200 tons O 2 /day $1.6M 9 tons O 2 /day $450K 0.3 tons O 2 /day $200K 2 tons O 2 /day $450K

26 Hypolimnetic Oxygenation Oxygenation systems Speece Cone (oxygen) side-stream supersaturation (oxygen) airlift aerator (air) bubble plume (air or oxygen) Want to predict performance In each case have gas transfer between individual (discrete) bubbles and water

27 Discrete Bubble Model Tracks individual bubbles rising in water Assumes no coalescence Accounts for changes in bubble volume: change in temperature change in hydrostatic pressure gas transfer of oxygen and nitrogen

28 Discrete Bubble Model J = K (HP C) L i dm dz = K (HP C) L i 4πr v b 2

29 Bubble Rise Velocity 100 Bubble Rise Velocity (cm s -1 ) 10 Tap Water Distilled Water Wüest et al. (1992) Rigid sphere equation Wave equation Bubble Diameter (mm)

30 Mass Transfer Coefficient 0.07 Mass Transfer Coefficient (cm s -1 ) Motarjemi and Jameson (1978) Wüest et al. (1992) Bubble Diameter (mm)

31 Model Validation Oxygen transfer tests in large tank Photographs to determine bubble size as function of gas flow rate Compare model predictions to experimental observations

32 Oxygen Transfer Tests TVA Engineering Lab Tank Height 14 m Tank Diameter 2 m

33 Bubble Size Measurement Water Depth 12.5 m Bubble Diameter 1.9 mm

34 Measured Bubble Size 3.0 Sauter Mean Diameter (mm) Depth = 6.7 meters Depth = 12.5 meters Gas Flow Rate per Unit Length Porous Hose (m 2 h -1 )

35 Oxygen Transfer Tests Nm 3 h Nm 3 h -1 Dissolved Oxygen (g m -3 ) Nm 3 h Time (min)

36 Discrete Bubble Model Validation Dissolved Oxygen (g m -3 ) Observed Predicted Time (min)

37 Model Application Hypolimnetic oxygenation systems airlift aerator (full-lift) [Lake Prince] bubble plume (linear) [Spring Hollow] bubble plume (circular) [Lake Hallwil] Predict oxygen transfer based on: gas (air or oxygen) flow rate initial bubble size

38 Airlift Aerator (full-lift) Lake Prince City of Norfolk Virginia

39 Lake Prince

40 Airlift Aerator

41 Airlift Aerator Model Validation Depth (m) Q air = m 3 s -1 Depth (m) Q air = m 3 s -1 Depth (m) Q air = m 3 s DO (g m -3 ) DO (g m -3 ) DO (g m -3 ) Depth (m) Q air = m 3 s -1 Depth (m) Q air = m 3 s -1 Depth (m) Q air = m 3 s DO (g m -3 ) DO (g m -3 ) DO (g m -3 )

42 Bubble Plume (linear) Spring Hollow Reservoir Western Virginia Water Authority Virginia

43 Spring Hollow Reservoir

44 Observed Oxygen in SHR Elevation (m) DO (mg/l) Julian Day (2001)

45 Oxygenation at Spring Hollow Max depth: 62 m Surface Area: 0.6 km 2 Volume: m 3 DO demand: ~50 kg / day Diffuser length: 620 m Oxygen flow: 20 SCFM (~35Nm 3 /h) Mass addition: ~ 1000 kg/day Efficiency: %

46 Bubble Plume Courtesy of Mark Mobley

47 Observed Temperature Sep 9-Sep Sep Elevation (m) _ Elevation (ft) _ 16-Sep 23-Sep 27-Sep 4-Oct 11-Oct 18-Oct 25-Oct 29-Oct Nov Nov Nov Temperature (C)

48 Observed Dissolved Oxygen Sep 9-Sep Sep Sep Elevation (m) _ Elevation (ft) _ 23-Sep 27-Sep 4-Oct 11-Oct 18-Oct 25-Oct 29-Oct Nov Nov Nov DO (mg/l)

49 Idealized Bubble Plume

50 Plume Model Flux Equations Water Volume Momentum Temperature Salinity Dissolved Gas (O 2 & N 2 ) Gas (O 2 & N 2 ) dq E dz = ρa ρ ρ w w ρp = glw + gλ[ L W(1 λ) ] dm dz df ρ T a dz = ET p dfs E asa dz = ρ 2 dfdi 4rN π = ECai + K L (HiPi C i ) dz v + v 2 dfgi 4rN π = K L (H i P i C i ) dz v + vb b ρ p

51 Plume Model Test Conditions Parameter July 2003 (Air) August 2003 (Oxygen) October 2004 (Oxygen) O 2 in gas supply (%) Entrainment coefficient, α (-) Plume radius ratio, λ (-) Initial plume area (m 2 ) Gas flow rate (Nm 3 hr -1 ) Bubble diameter (mm) Diffuser depth (m)

52 Temperature and DO Contours Depth (m) Depth (m) 2 July ( o C) Distance from Diffuser (m) 2 July (g/m 3 ) Distance from Diffuser (m) Depth (m) Depth (m) 17 August October ( o C) Distance from Diffuser (m) 17 August (g/m 3 ) Distance from Diffuser (m) Depth (m) Depth (m) ( o C) Distance from Diffuser (m) 23 October (g/m 3 ) Distance from Diffuser (m)

53 Plume Boundary Conditions 0 a) 0 b) Depth (m) July Aug Oct Temperature ( ο C) Depth (m) July Aug Oct Dissolved Oxygen (g/m 3 )

54 Linear Plume Model Validation a) b) Depth (m) July Aug Oct 2004 Depth (m) July Aug Oct Plume Temperature ( ο C) Dissolved Oxygen (g/m 3 )

55 Bubble Plume (circular) Lake Hallwil Canton Aargau Switzerland

56 Lake Hallwil M2 30 N M km 20 10

57 Measurements CTD and ADCP

58 Temp ( o C) 24 July Depth (m) Distance from Diffuser (km) Depth (m) September Distance from Diffuser (km) 5.8

59 North velocity (mm/s) Persistent Seiching Depth: m m m m -50 Jun 13 Jun 15 Jun 17 Jun 19

60 DO (g m -3 ) July Depth (m) Distance from Diffuser (km) 0 Depth (m) September Distance from Diffuser (km)

61 Bubble Plume Diffuser

62 Temperature Contours Depth (m) Distance from center line (m) ( o C)

63 Oxygen Contours Depth (m) Distance from centerline (m) (gm -3 ) 0

64 Circular Plume Model Validation Depth (m) DO (g m -3 ) and Temperature ( C) Average Plume DO Predicted DO Average Plume Temperature Predicted Temperature

65 Story so far Why we need oxygenation How various devices work Suite of process models that we can use to predict performance Points to remember: All devices induce mixing in lake/reservoir Lake/reservoir influences performance of oxygenation system (especially bubble plume) Sediment oxygen demand drives oxygen consumption

66 Sediment Oxygen Demand SOD, which typically governs hypolimnetic DO depletion, often assumed constant Some oxygenation systems fail to meet reservoir oxygen demand due to diffuser-induced SOD

67 Carvin s Cove Reservoir Maximum depth (m) 23 Surface area (km 2 ) 2.5 Volume (m 3 ) Avg. length width (m)

68 Oxygenation at Carvin s Cove Dam B C A Diffuser lines Trophic status Eutrophic Oxygen demand (kg/day) ~ 430 Typical stratification period March thru November Diffuser length (m) 1250 (2 625 m diffuser lines)

69 Oxygenation System Photograph by Josh Meltzer Photograph by Josh Meltzer

70 Carvin s Cove Reservoir Soluble Fe Diffuser Installed Aug 1, 05 Off (Jun 15, 06) On (Jul 12, 06) Elevation (m) Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan

71 Carvin s Cove Reservoir Soluble Mn Diffuser Installed Aug 1, 05 Off (Jun 15, 06) On (Jul 12, 06) Elevation (m) Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07

72 Observed Temperature Jul 1-Aug 8-Aug 351 x Aug Elevation (m) Sample Location (x) Elevation (ft) 25-Aug 29-Aug 5-Sep 12-Sep 22-Sep 6-Oct Oct 20-Oct Oct Temperature (C) 3-Nov

73 Observed Dissolved Oxygen Jul 1-Aug 8-Aug 351 x Aug Elevation (m) Sample Location (x) Elevation (ft) 25-Aug 29-Aug 5-Sep 12-Sep 22-Sep 6-Oct Oct 20-Oct Oct DO (mg/l) 3-Nov

74 Calculated Oxygen Demand HODmass (kg day -1 ) _ CCR y = 22x SHR y = 6.3x Oxygen Flow Rate (NCMH) Carvins Cove Reservoir Spring Hollow Reservoir

75 Measurements Lander, ADCP and Peepers 1. Profiling lander with microsensors: O 2, temp, redox and ph at SWI 2. In-lab O 2 microsensor measurements of sediment cores: O 2 profile data 3. Acoustic Doppler current profiler: water column velocity profile data 4. Diffusive porewater analyzers (peepers): soluble Fe and Mn profile data Maximum depth (m) 23 Surface area (km 2 ) Volume (m 3 ) Avg. length width (m)

76 Sediment Oxygen Demand Turbulence within bottom boundary layer (BBL) controls diffusive boundary layer (DBL) thickness and sediment-water fluxes 3 2 BBL mixing depth (mm) DBL Sediment oxic zone, z max Fick' s First Flux O 2 (μmol L -1 ) Law of dc = φd dz C = φd Diffusion C δ bulk DBL SWI φ = porosity D = (unity in diffusion coefficient water)

77 Correlation between extent of sediment oxic zone and HOx flow rate 2.5 zmax-flow C3 avg R² = zmax-flow CVCB avg R² = z max (mm) Flow (m 3 hr -1 ) C3 Increased flow directly related to enhanced sediment oxic zone Analogous results from study on hypolimnetic O 2 demand CVCB 77

78 Carvin s Cove Reservoir HOx flow regime for summer Flow (m 3 hr -1 ) C Jun 1-Jul 15-Jul 29-Jul 12-Aug 26-Aug 9-Sep

79 Response of vertical O 2 distribution near the SWI and in the hypolimnion after turning HOx off Depth (m) c b -60 O 2 (μmol L -1 ) J O2 (mmol m -2 d -1 ), C SWI (10-1 μmol L -1 ) a JO2 J CswiC SWI DBL δ DBL HOx turned off DBL thickness, δ DBL (mm) 1E06 Depth (mm) Depth (mm) a SWI SWI /7 8/14 8/21 8/28 9/4 9/11 Time (m/d) 0

80 Variation in Fe and Mn at the SWI in response to HOx operations Soluble Fe 15 Soluble Mn Increased sediment O2 availability 120 d /29 Fe and Mn suppressed near SWI 15 Flow (m3 hr -1) During HOx operation: Depth (cm) a 6/8 7/18 8/27 10/ date (m/d) 4/29 11/15 6/8 7/18 8/27 10/ date (m/d) 11/ b e /29 6/8 7/18 8/27 10/ date (m/d) 11/ /8 7/18 8/27 10/ date (m/d) f /28 8/ date (m/d) 9/6 6/ / / /15 5 c /8 7/28 8/ date (m/d) 9/6 0 Flow (m3 hr -1) Depth (cm) 10 4/29 Flow (m3 hr -1) Depth (cm) 1300 Fe Mn (μmol L-1)

81 Reservoir Dynamics June 1, 06 Carvins Cove Dissolved Oxygen [Oxygenation: 68 NCMH (40 SCFM)] Intakes Open Elevation (m) SCFM increased to 40 SCFM Distance (m)

82 Reservoir Dynamics June 6, 06 Carvins Cove Dissolved Oxygen [Oxygenation: 68 NCMH (40 SCFM)] Intakes Open Elevation (m) Distance (m)

83 Use Si3D for Coupled Model Si3D is a 3-D, free surface hydrodynamic reservoir model Continuity equation for incompressible fluid Navier-Stokes equations for momentum Transport equation for temperature Extensively validated 3D Grid of Spring Hollow Reservoir in Si3D

84 Use Si3D for Coupled Model To couple the plume model with Si3D, sink and source terms were added Plume model predicts entrainment flow rate as well as detrainment flow rate Q d and depth Si3D provides boundary conditions for plume model Cell size = 15 m x 15 m x 1 m

85 Coupled Plume Model Validation Coupled model predictions with plume turned OFF Coupled model predictions with plume turned ON

86 Coupled Plume Model Prediction

87 Current Focus Complex reservoir dynamics coupled reservoir model that includes bubble plume + sediment oxygen demand In-situ oxidation of Fe and Mn and reduction of internal P loading Design and operation of sidestream supersaturation systems Potential control of algal growth with epilimnetic mixing