Cortez Sanitation DistrictSeptember 2002 Arber Cortez UV Disinfection Steven M. Ravel, P.E. Travis E. Meyer, P.E. Richard P. Arber Associates

Cortez Sanitation District September 2002

Arber

Cortez UV Disinfection

Steven M. Ravel, P.E. Travis E. Meyer, P.E.

Richard P. Arber Associates


Arber Introduction

• Background• Selection of UV Lamp Type• Specifying UV Dose• Verification of UV Dose


Arber Background

• New WWTP for Cortez Sanitation District

• Treatment Train– Headworks– Extended Aeration– Secondary Clarification– UV Disinfection


Arber Background

• Design Flows– Average: 1.8 mgd– Peak Month: 2.1 mgd– Peak Hour: 7 mgd


Arber UV Lamp Types Considered

• Medium Pressure• Low Pressure / Low Intensity• Low Pressure / High Intensity


Arber Medium Pressure

• Advantages– Lowest Number of Lamps

Required– UV Intensity Adjustable– Sleeve Wipers Available– Low Space Requirement– Open Channel and Closed Pipe

Systems Available


Arber Medium Pressure

• Disadvantages– Low Efficiency (Approximately

10 - 20%– Higher Capital Cost (for these

flow rates)– Require warm-up period on

start-up


Arber Low Pressure / Low Intensity

• Advantages– Low Capital Cost– High Efficiency

(Approximately 40%)– Simple Design / Simple

Operation


Arber Low Pressure / Low Intensity

• Disadvantages– Highest Number of Lamps

Required– UV Intensity Not Adjustable– Sleeve Wipers Not Available– High Maintenance (Lamp

Replacement and Cleaning)– High Space Requirement


ArberLow Pressure / High Intensity

(Selected)

• Advantages– Low Capital Cost– High Efficiency

(Approximately 40%)– Less Lamps Required than

Low/Low (Approximately 1/4)– UV Intensity Adjustable– Sleeve Wipers Available


ArberLow Pressure / High Intensity

(Selected)

• Disadvantages– Relatively Short Track Record

Compared to Low/Low and Medium

– More Lamps Required than Medium


Arber Specifying UV Dose

• EPA UVDIS Computer Model• BioAssay• Performance Based


Arber UVDIS Computer Model

• Advantages– Computer program easy and

fast to run– Theoretical model developed

by EPA


Arber UVDIS Computer Model

• Disadvantages– Program designed for Low/Low

systems• May not be as applicable for

Low/High or Medium Systems

– Model results must be adjusted using high safety factors to ensure system will perform as required


Arber BioAssay

• Advantages– System sized based on dose

response curve for actual equipment to be installed

– Dose response curve developed for site specific wastewater effluent quality


Arber BioAssay

• Disadvantages– No Standard Protocol for BioAssay

• Detailed protocol must be developed to compare results for different systems

– Expensive and Time-Consuming– If MS-2 Phage used for bioassay,

correlation must be developed to translate results for fecal coliform


Arber Performance Based

• Advantages– Specify what you want the

system to do, let manufacturers design their system to do it

– Most direct method to specify


Arber Performance Based

• Disadvantages– Relying on manufacturers to

design adequate system– Must determine a method to

check performance in the field


Arber Cortez Sanitation District

• Pre-selection of UV System based on:– Primary UV Dose Criteria:

Performance for Fecal Coliform• In: 500,000/100 mL• Out: 200/100 mL

– Secondary UV Dose Criteria:• Min UV Dose of 30,000 µw/cm2

based on UVDIS


Arber Cortez Sanitation District

– Other Design Criteria• Minimum Flow: 1 mgd• Average Flow: 1.8 mgd• Peak Hydraulic Flow: 7 mgd• Peak Process Flow: 5 mgd• UV Transmittance: 65%• TSS: 30 mg/l• Number of Channels: 2• Number of Banks/Channel: 2


Arber Comparison of UV SystemsMfr A Mfr B

# of Lamps 48 64

Capital Cost $100,000* $110,000

Annual O&M Costs

Electricity $1,400 $3,000

Lamps $1,900 $3,200

Total $3,300 $6,200

NPV (20 yrs, 6%) $140,000 $180,000

* Includes Separate Sunshade Structure for Ballast and Controls


Arber Verifying UV Dose

• During Performance Test, Need to Account for Differences (Design vs. Actual) in:– Flow– UV Transmittance– Lamp Age (70% output)– Fecal Coliforms


Arber Flow Adjustment

• Adjust UV system output in proportion to difference in flow

• Example: Design flow = 5 MGD, Actual flow = 1 mgd:Adjust UV system output to 20% of maximum


Arber Transmissivity Adjustment

• Adjust UV system output based on correlation between design UVT and actual UVT

0

0.5

1

1.5

2

2.5

3

30% 40% 50% 60% 70% 80% 90% 100%

Transmissivity

UV

Out

put F

acto

r


Arber Fecal Coliform Adjustment

• Two Options– Spike UV influent to bring fecal

coliform up to design number– Lower effluent fecal coliform

requirement to achieve same log reduction as design


ArberCortez Sanitation District

• Turn down UV system output to min during performance test.

• Schedule test for highest flow, lowest UVT, highest Fecal

• Record Flow Rate• Test Fecal Coliforms (In vs.Out)• Test UVT• Make determination of performance

based on available data


Arber Conclusions

• Low Pressure / High Intensity best solution for Cortez

• Performance based spec on fecal coliform with min UV dose based on EPA UVDIS

• Verification of UV Dose using best available data at time of performance test

Documents

Cortez Sanitation DistrictSeptember 2002 Arber Cortez UV Disinfection Steven M. Ravel, P.E. Travis E. Meyer, P.E. Richard P. Arber Associates