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Ultraviolet Light Process Model Evaluation. Presented by: Jennifer Hartfelder, P.E. Brown and Caldwell. Models to Evaluate UV Performance. USEPA Mathematical Protocol – USEPA Design Manual Municipal Wastewater Disinfection

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Ultraviolet light process model evaluation l.jpg

Ultraviolet Light Process Model Evaluation

Presented by:

Jennifer Hartfelder, P.E.

Brown and Caldwell

Models to evaluate uv performance l.jpg
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

Uv process design model l.jpg
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

Usepa step 1 calculate reactor uv density l.jpg
USEPA - Step 1Calculate Reactor UV Density

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USEPA - Step 2Calculate Intensity

  • Biological Assay

  • Direct Calculation Method

Intensity field point source summation method l.jpg
Intensity FieldPoint Source Summation Method

Average intensity l.jpg
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

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USEPA - Step 3Determine Inactivation Rates

  • K = aIavgb

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USEPA - Step 4Determine 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 5Determine UV Loading

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

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USEPA - Step 6Establish Performance Goals

  • Np = cSSm

  • N’ = N - Np

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USEPA - Step 7Calculate 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

Uvdis input l.jpg

Arc length

Centerline spacing

Watts output

Quartz Sleeve Diameter

No. of banks in series

Aging Factor

Fouling Factor


Dispersion Coefficient

Average Intensity

Number of lamps


Percent transmissivity


Nwri awwarf protocol l.jpg

  • 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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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: 50 - 100 mW-sec/cm2

  • NWRI/AWWARF based on upstream filtration:

    • Media - 100 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

Usepa mathematical protocol l.jpg


Apply same calculations to all systems

Can be used for uniform, staggered, concentric, and tubular lamp arrays


Least conservative

Assumes flow perpendicular to lamp

USEPA Mathematical Protocol

Uvdis l.jpg


HydroQual is in the process of updating the program to address some of the cons

More conservative than USEPA protocol


Less conservative than bioassay

For low-pressure systems only

For flow parallel to lamps only

Dispersion coefficient, E, is assumed


Nwri awwarf protocol25 l.jpg


Most conservative

May assume a conservative required dose (50 to 100 mW-sec/cm2)


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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  • 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