Ultraviolet Light Process Model Evaluation Presented by: Jennifer Hartfelder, P.E.

Brown and Caldwell

Models to Evaluate UV Performance   UVDIS – Software Developed by HydroQual, Inc. based on the USEPA Mathematical Protocol  USEPA Mathematical Protocol –

USEPA Design Manual Municipal Wastewater Disinfection

NWRI/AWWARF Protocol –

Ultraviolet Disinfection Guidelines for Drinking Water and Water Reuse

UV Process Design Model  Chick’s Law: N = N o e -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 1. Liquid volume per lamp: V v lamp          d q 2 4  z    2. Density: D   z  nominal V v UV output  lamp

USEPA - Step 2 Calculate Intensity  Biological Assay  Direct Calculation Method

Intensity Field Point Source Summation Method

Intensity vs. UV Density

Lamp Configuration

Average Intensity  I avg = (nominal I avg )(F p )(F t )  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

USEPA - Step 3 Determine Inactivation Rates  K = aI avg b

USEPA - Step 4 Determine Dispersion Coefficient  Establish relationship between x and u  h L = c f (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 cm 2 /sec

USEPA - Step 5 Determine UV Loading N ' N o t n      V Q v W n W n      exp       2 E   1  ux 4 KE u 2 1 / 2        Plot log(N’/No) vs. Q/Wn and u vs. Q/Wn

USEPA - Step 6 Establish Performance Goals  N p = cSS m  N’ = N - N p

USEPA - Step 7 Calculate Reactor Sizing  Number of lamps required:  Q/W n – determined from the log (N’/N maximum loading graphs developed in Step 5 for the N’ developed in Step 6 o ) vs.  Lamps required = Q/(Q/W n )/W n

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/cm 2 US wastewater industry standard: 30 mW-sec/cm 2 CDPHE WWTP design criteria: 30 mW-sec/cm 2 US reuse standard: 50 - 100 mW-sec/cm 2 NWRI/AWWARF based on upstream filtration:  Media - 100 mW-sec/cm 2   Membrane - 80 mW-sec/cm 2 Reverse Osmosis - 40 mW-sec/cm 2

Protocol Evaluation  For peak hour conditions:  Q = 3.5 MGD (9,200 lpm)  SS = 45 mg/L   N o = 1.50E+06 No./100 mL N = 6,000 No./100 mL  Transmittance = 60%  Allowable headloss = 1.5 inches

System Specific Design Criteria Parameter Arc length (cm) S x (cm) S y (cm) D q (cm) W uv (watts) Staggered Array F t F p Trojan 3000Plus Wedeco TAK55 147 143 7.6

7.6

1.5

100 No 0.7

0.7

13 13 4.8

125 No 0.7

0.7

Number of Bulbs Required Utilizing Various Sizing Methods

Sizing Method

USEPA Mathematical Protocol UVDIS Software Program Bioassay Manufacturer’s Recommendation

Trojan UV3000Plus

35

Wedeco TAK55

25 42 48 48 40 55 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  Most conservative  May assume a conservative required dose (50 to 100 mW-sec/cm 2 )  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