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Predictive Performance Scaling Method for Hydrodynamic Separators Mark B. Miller, P.G. Research Scientist Chattanooga, Tennessee (888) EPA Region 6 MS4 Stormwater Conference July 27 – August 1, 2014 Ft. Worth, Texas

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? How do I predict an HDS performance curve for a different particle size than the performance curve derived from using the HDS’s lab test sediment’s particle size distribution? GET OUT YOUR SLIDE RULE… OR YOUR TI-30.

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Topics of Discussion Overview of Hydrodynamic Separators (HDSs) Overview of Hydrodynamic Separators (HDSs) The Problem: Evaluating Lab Performance Tests A Solution: Performance Prediction Method Calculations, Tables & Graphs Example Comparison of HDS #1 to HDS #2 Texas DOT Specification Example for 70% annual TSS removal and d 50 = 75 µm for µm PSD

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ReferenceReference

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Derivation of Peclet Number

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Some Examples of Hydrodynamic Separators

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Types of Hydrodynamic Separators Vortex type = Gravitational & Centrifugal Forces Captures sediment, debris, free-floating oil, floatables Vault type = Gravitational Forces

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LID Technology Selection Pyramid

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Pretreatment or Standalone Hydrodynamic Separator Applications Off-lineOn-line

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HDS Verifications and Use Level Designations “TARP” (New Jersey) Technology Acceptance Reciprocity Partnership Protocol for Stormwater BMP Demonstrations New Jersey DEP Lab Test Protocol for HDSs 1/25/13 now applies, no field test req’d NJ PSD 1-1,000 µm, Scour test 50-1,000 µm for on-line HDS NJDEP Certification for HDSs limited to 50% TSS removal credit regardless if higher rate achieved in lab or field test Field test per TARP Tier II 2003/2006 NJDEP 2009 protocol expires w/ new lab test Sizing based on MTFR for net annual TSS removal “TAPE” (Washington) Technology Assessment Protocol – Ecology Use Level Designations GULD and CULD require field test in Pacific NW, lab data may supplement PULD based on lab test Influent TSS <100 mg/L, Effluent <20 mg/L Influent TSS mg/L, Effluent ≥80% removal Influent TSS >200 mg/L, Effluent >80% removal ULDs for Dissolved Metals (Cu, Zn), Total Phosphorus, Oil (TPH), Pretreatment for TSS Sizing based on 80% TSS removal per storm event

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Evaluating HDS Laboratory Performance Testing FRUSTRATION We’ll explore NJCAT Lab Test Verifications and try to reduce the level of FRUSTRATION you may have when evaluating reports and results

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* Author does not guarantee accuracy of report interpretations

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* NJDEP 1/25/13 lab protocol d50 <75 µm

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Steps for Predictive Performance Method 1. Calculate: Pe = (d · h · Vs) / Q using lab test data 2. Solve for: Q = (d · h · Vs) / Pe 3. Convert Q to surface area loading rate (gpm/ft 2 ) 4. Make table for RE% vs. Loading Rate 5. Plot performance curve for selected particles size 6. Make sizing chart(s) for: a)per storm TSS removal, or b)annual TSS removal

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Peclet Number Peclet Number can be used to predict performance between different particle sizes Pe = advection diffusion Pe = advection diffusion “Peclet Number is defined as the ratio of advection to diffusion, where advective settling forces are opposed by turbulent diffusion in the system tending to keep solids in suspension.” (SAFL)

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Peclet Number (Pe) Pe = (d · h · Vs) / Q Pe = Unitless d = Horizontal flow dimension in feet h = Vertical flow dimension in feet Vs = Particle settling velocity in feet/sec Q = Flow rate in cubic feet/second d in Vortex HDS = diameter of effective treatment area d in Vortex HDS = diameter of effective treatment area d in Vault HDS = long axis of effective treatment area (parallel to flow) d in Vault HDS = long axis of effective treatment area (parallel to flow)

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Three Assumptions for Peclet Number (SAFL): 1.Settling Velocity assumes equivalent spherical particle shapes. 2. Mixing dynamics, and associated removal efficiency, scales with size (diameter and depth) for each device. 3. Turbulent diffusion coefficient (Dt) scales with Q/d across the range of tested flow rates.

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Method Variables & Assumptions 1.Stoke’s Law for particle settling velocity using: a)Specific gravity = 2.65 b)Water temperature 20°C (68°F) c)Other constant variables for Vs calculation 2.100% TSS Removal Zero Loading Rate 3.Calculations based on median (d50) particle size, not full particle size distribution 4.Performance curve profile does not change for different d50 simulations, but expected to change more as d50 decreases below ~ 50 µm (presently undefined).

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Calculate Pe: HDS #1 Test Parameters Q (cfs) Loading Rate (gpm/ft²) RE (%) Pe (unitless) d 50 = 110 µm (OK-110)00100NA Vs = ft/s SG = D = 3.3 ft h = 3.83 ft Example: Q = 0.2 cfs Pe = (3.3 ft · 3.83 ft · ft/sec) / 0.2 cfs = 1.33 Pe = (d · h · Vs) / Q

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TermVariableUnitsDescription Gs2.65Specific gravity of particle ρsρs lb/ft 3 Density of particle ρwρw 62.29lb/ft 3 Density of water g32.20ft/s 2 Acceleration due to gravity T20.00C°Temperature of water T68F°Temperature of water μ2.09E-05lb*s/ft 2 Dynamic viscosity of water at given temp. υ1.08E-05ft 2 /sKinematic Viscosity of water D110micronDiameter of particle Vs0.024ft/sSettling velocity, Cheng Formula Vs ft/sSettling velocity, Stoke's Law Vs0.029ft/sSettling velocity, Ferguson & Church Calculate Particle Settling Velocity (Vs) Input Value

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Particle Size (µm) Vs (ft/sec) Stoke’s Law Particle Settling Velocities

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Performance Summary - 45 µm Parameters Q (cfs) Loading Rate (gpm/ft²) RE (%) Pe (unitless) d 50 = 45 µm00100NA Vs = ft/sec SG = d = 3.3 ft (8.3 ft 2 ) h = 3.83 ft Rearrange equation to solve for Q Q = (3.3 ft · 3.83 ft · Vs) / Pe RE and Pe constant Loading Rate = Q cfs · gpm/cfs / Area ft 2

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50 µm Parameters Q (cfs) Loading Rate (gpm/ft²) RE (%) Pe (unitless) d 50 = 50 µm00100 NA Vs = ft/sec SG = D = 3.3 ft h = 3.83 ft µm (d 50 from NJDEP PSD) Parameters Q (cfs) Loading Rate (gpm/ft²) RE (%) Pe (unitless) d 50 = 67 µm00100 NA Vs = ft/sec SG = D = 3.3 ft h = 3.83 ft

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75 µm Parameters Q (cfs) Loading Rate (gpm/ft²) RE (%) Pe (unitless) d 50 = 75 µm00100NA Vs = ft/sec SG = D = 3.3 ft h = 3.83 ft µm Parameters Q (cfs) Loading Rate (gpm/ft²) RE (%) Pe (unitless) d 50 = 90 µm00100 NA Vs = ft/sec SG = D = 3.3 ft h = 3.83 ft

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110 µm (lab test) Parameters Q (cfs) Loading Rate (gpm/ft²) RE (%) Pe (unitless) d 50 = 110 µm00100NA Vs = ft/sec SG = D = 3.3 ft h = 3.83 ft µm Parameters Q (cfs) Loading Rate (gpm/ft²) RE (%) Pe (unitless) d 50 = 125 µm00100NA Vs = ft/sec SG = D = 3.3 ft h = 3.83 ft

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45 µm50 µm67 µm75 µm90 µm110 µm125 µm RE (%) LR gpm/ft 2 RE (%) LR gpm/ft 2 RE (%) LR gpm/ft 2 RE (%) LR gpm/ft 2 RE (%) LR gpm/ft 2 RE (%) LR gpm/ft 2 RE (%) LR gpm/ft HDS #1 Performance Summary Note: Removal efficiencies are constant for each particle size

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* NJDEP 1/25/13 lab protocol d50 <75 µm

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HDS #2: 63 µm Lab Test (Calculate Pe) Parameters Q (cfs) Loading Rate (gpm/ft²) RE (%) Pe (unitless) d 50 = 63 µm00100NA Vs = ft/sec SG = D = 5 ft (19.6 ft 2 ) h = 2.6 ft HDS #2: 110 µm by Peclet Method Parameters Q (cfs) Loading Rate (gpm/ft²) RE (%) Pe (unitless) d 50 = 110 µm00100NA Vs = ft/sec SG = D = 5 ft (19.6 ft 2 ) h = 2.6 ft HDS #2 Performance

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HDS #1: 110 µm Lab Test Parameters Q (cfs) Loading Rate (gpm/ft²) RE (%) Pe (unitless) d 50 = 110 µm00100NA Vs = ft/sec SG = D = 3.3 ft (8.3 ft 2 ) h = 3.83 ft HDS #1: 63 µm by Peclet Method Parameters Q (cfs) Loading Rate (gpm/ft²) RE (%) Pe (unitless) d 50 = 63 µm00100NA Vs = ft/sec SG = D = 3.3 ft (8.3 ft 2 ) h = 3.83 ft

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HDS #1 Particle Size and Peak Loading Rate for 80% TSS Removal Efficiency Per Storm Particle Size (µm) Peak Loading Rate (gpm/ft 2 )* * * Exact Loading Rate can be calculated using equation for slope of performance curve

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Example HDS Model Diameter (ft) Effective Treatment Area (ft 2 ) Particle Size and Loading Rate 45 µm50 µm67 µm75 µm90 µm110 µm125 µm 10.5 gpm/ft gpm/ft gpm/ft gpm/ft gpm/ft gpm/ft gpm/ft 2 WQTF (cfs) Water Quality Treatment Flow = (Area · Loading Rate) / gpm/cfs Example: 1.4 cfs for 75 µm = HDS Model 8 ft diameter Example HDS #1 Sizing Charts: 80% TSS Removal per Storm

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Special Specification 5848 “The SWTU shall be capable of removing at least 70% of the net annual Total Suspended Solids (TSS) based on a typical gradation of microns with a d50-micron particle size of 75; remove particles greater than 150 –microns (sand-size particles); capture and retain 100% of pollutants greater than 1 inch in size based on the objects smallest dimension; and capture and retain total petroleum hydrocarbons.”

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75 µm TXDOT Specification - HDS #1 Q 75 (cfs) Loading Rate (gpm/ft 2 ) RE (%) Pe Given Q 110 µm (cfs) Q 75/Q 110 % Flow 75 µm/110 µm 00100NA / / / / HDS lab test showed 80% net annual TSS removal up to 100 gpm/ft 2. Make sizing chart based on peak flow, 66.6% of 100 gpm/ft 2, or 66.6 gpm/ft 2

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80% net annual TSS 100 gpm/ft 2

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HDS Model Diameter (ft) Treatment Area (ft 2 ) Water Quality Treatment 66.7 gpm/ft 2 (cfs) WQTF = (Treatment Area · Loading Rate) / gpm/cfs WQTF = (X.X ft 2 · 66.7 gpm/ft 2 ) / gpm/cfs TXDOT HDS Sizing Chart for HDS #1 80%* Annual TSS Removal for 75 µm * Exceeds specification of 70% annual TSS removal

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Here’s the steps to follow: 1. Calculate: Pe = (d · h · Vs) / Q using lab test data 2. Solve for: Q = (d · h · Vs) / Pe 3. Convert Q to surface area loading rate (gpm/ft 2 ) 4. Make table for RE% vs. Loading Rate 5. Plot performance curve for selected particles size 6. Make sizing chart(s) for: a)per storm TSS removal efficiency, or b)annual TSS removal efficiency 7.Brag to boss how you solved a mystery of stormwater life

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Mark Miller

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