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**Ultraviolet Light Process Model Evaluation**

Presented by: Jennifer Hartfelder, P.E. Brown and Caldwell

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**Models to Evaluate UV Performance**

USEPA Mathematical Protocol – USEPA Design Manual Municipal Wastewater Disinfection UVDIS – Software Developed by HydroQual, Inc. based on the USEPA Mathematical Protocol NWRI/AWWARF Protocol – Ultraviolet Disinfection Guidelines for Drinking Water and Water Reuse

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**UV Process Design Model**

Chick’s Law: N = Noe-kIt N = bacterial concentration remaining after exposure to UV No = initial bacterial concentration k = rate constant I = intensity of UV t = time of exposure

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**USEPA - Step 1 Calculate Reactor UV Density**

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**USEPA - Step 2 Calculate Intensity**

Biological Assay Direct Calculation Method

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**Intensity Field Point Source Summation Method**

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**Intensity vs. UV Density**

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Lamp Configuration

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**Average Intensity Iavg = (nominal Iavg)(Fp)(Ft)**

Fp = the ratio of the actual output of the lamps to the nominal output of the lamps Ft = the ratio of the actual transmittance of the quartz sleeve or Teflon tubes to the nominal transmittance of the enclosure Fp = 0.7 Ft = 0.5 to 0.7 quartz sleeve, 0.4 to 0.6 Teflon tubes

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**USEPA - Step 3 Determine Inactivation Rates**

K = aIavgb

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**USEPA - Step 4 Determine Dispersion Coefficient**

Establish relationship between x and u hL = cf(x)(u)2 Plot log(u) and log(x) versus log(ux) Dispersion number, d d = E/(ux) d = 0.03 to 0.05 E = 50 to 200 cm2/sec

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**USEPA - Step 5 Determine UV Loading**

Plot log(N’/No) vs. Q/Wn and u vs. Q/Wn

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**USEPA - Step 6 Establish Performance Goals**

Np = cSSm N’ = N - Np

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**USEPA - Step 7 Calculate Reactor Sizing**

Number of lamps required: Q/Wn – determined from the log (N’/No) vs. maximum loading graphs developed in Step 5 for the N’ developed in Step 6 Lamps required = Q/(Q/Wn)/Wn

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**UVDIS Input Arc length Centerline spacing Watts output**

Quartz Sleeve Diameter No. of banks in series Aging Factor Fouling Factor Flow Dispersion Coefficient Average Intensity Number of lamps Staggered Percent transmissivity

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UVDIS Output

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NWRI/AWWARF Protocol Determine UV inactivation of selected microorganisms under controlled batch conditions by conducting a bioassay Dose-Response Curves Microorganism MS-2 bacteriophage E. coli Pilot vs. full scale study

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Bioassay Results

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**UV Dose German drinking water standard: 40 mW-sec/cm2**

US wastewater industry standard: 30 mW-sec/cm2 CDPHE WWTP design criteria: 30 mW-sec/cm2 US reuse standard: mW-sec/cm2 NWRI/AWWARF based on upstream filtration: Media mW-sec/cm2 Membrane - 80 mW-sec/cm2 Reverse Osmosis - 40 mW-sec/cm2

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**Protocol Evaluation For peak hour conditions: Q = 3.5 MGD (9,200 lpm)**

SS = 45 mg/L No = 1.50E+06 No./100 mL N = 6,000 No./100 mL Transmittance = 60% Allowable headloss = 1.5 inches

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**System Specific Design Criteria**

Parameter Trojan 3000Plus Wedeco TAK55 Arc length (cm) 147 143 Sx (cm) 7.6 13 Sy (cm) Dq (cm) 1.5 4.8 Wuv (watts) 100 125 Staggered Array No Ft 0.7 Fp

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**Number of Bulbs Required Utilizing Various Sizing Methods**

Trojan UV3000Plus Wedeco TAK55 USEPA Mathematical Protocol 35 25 UVDIS Software Program 42 40 Bioassay 48 55 Manufacturer’s Recommendation 34

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**USEPA Mathematical Protocol**

Pros Apply same calculations to all systems Can be used for uniform, staggered, concentric, and tubular lamp arrays Cons Least conservative Assumes flow perpendicular to lamp

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UVDIS Pros HydroQual is in the process of updating the program to address some of the cons More conservative than USEPA protocol Cons Less conservative than bioassay For low-pressure systems only For flow parallel to lamps only Dispersion coefficient, E, is assumed

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**NWRI/AWWARF Protocol Pros Cons Most conservative**

May assume a conservative required dose (50 to 100 mW-sec/cm2) Cons Bioassay tests have not been conducted yet for all systems Bioassay is costly Scale-up issues Bioassays have not used the same protocol (i.e., microorganism) More research on how to select required dose is necessary

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**Conclusions Bioassay is most conservative sizing method**

More research required: Dose selection protective of human health Scale-up issues Target organism Engineer should require a field performance test and performance bond

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