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

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 1Calculate Reactor UV Density

1. Liquid volume per lamp:

z

4

d - zs

lamp

V2q2v

2. Density:

lamp

Voutput UVnominalz

Dv

USEPA - Step 2Calculate Intensity

Biological Assay Direct Calculation Method

Intensity FieldPoint 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

USEPA - Step 3Determine Inactivation Rates

K = aIavgb

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

USEPA - Step 5Determine UV Loading

n

n

v

n

W

Q

W

V

t

2/1

2

o

'

u

KE411E2

uxexp

N

N

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

USEPA - Step 6Establish Performance Goals

Np = cSSm

N’ = N - Np

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

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 bacteriophageE. 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: 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

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) 7.6 13

Dq (cm) 1.5 4.8

Wuv (watts) 100 125

Staggered Array No No

Ft 0.7 0.7

Fp 0.7 0.7

Number of Bulbs Required Utilizing Various Sizing Methods

Sizing Method Trojan UV3000Plus

Wedeco TAK55

USEPA Mathematical Protocol

35 25

UVDIS Software Program 42 40

Bioassay 48 55

Manufacturer’s Recommendation

48 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/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