# Ultraviolet Light Process Model Evaluation

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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 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
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

USEPA - Step 2 Calculate Intensity
Biological Assay Direct Calculation Method

Intensity Field Point Source Summation Method

Intensity vs. UV Density

Lamp Configuration

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

USEPA - Step 3 Determine Inactivation Rates
K = aIavgb

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

USEPA - Step 5 Determine UV Loading
Plot log(N’/No) vs. Q/Wn and u vs. Q/Wn

USEPA - Step 6 Establish Performance Goals
Np = cSSm N’ = N - Np

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

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

UVDIS Output

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

Bioassay Results

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

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

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

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

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

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

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

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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