1. Ultraviolet Light Process Model Evaluation
Presented by:
Jennifer Hartfelder, P.E.
Brown and Caldwell

2. 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

3. 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

4. USEPA - Step 1 Calculate Reactor UV Density

5. USEPA - Step 2 Calculate Intensity
Biological Assay
Direct Calculation Method

6. Intensity Field Point Source Summation Method

7. Intensity vs. UV Density

8. Lamp Configuration

9. 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

10. USEPA - Step 3 Determine Inactivation Rates
K = aIavgb

11. 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

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

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

14. 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

15. 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

16. UVDIS Output

17. 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

18. Bioassay Results

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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