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

Cortez Sanitation DistrictSeptember 2002 Arber Introduction Background Selection of UV Lamp Type Specifying UV Dose Verification of UV Dose

Cortez Sanitation DistrictSeptember 2002 Arber Background New WWTP for Cortez Sanitation District Treatment Train –Headworks –Extended Aeration –Secondary Clarification –UV Disinfection

Cortez Sanitation DistrictSeptember 2002 Arber Background Design Flows –Average: 1.8 mgd –Peak Month: 2.1 mgd –Peak Hour: 7 mgd

Cortez Sanitation DistrictSeptember 2002 Arber UV Lamp Types Considered Medium Pressure Low Pressure / Low Intensity Low Pressure / High Intensity

Cortez Sanitation DistrictSeptember 2002 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

Cortez Sanitation DistrictSeptember 2002 Arber Medium Pressure Disadvantages –Low Efficiency (Approximately % –Higher Capital Cost (for these flow rates) –Require warm-up period on start- up

Cortez Sanitation DistrictSeptember 2002 Arber Low Pressure / Low Intensity Advantages –Low Capital Cost –High Efficiency (Approximately 40%) –Simple Design / Simple Operation

Cortez Sanitation DistrictSeptember 2002 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

Cortez Sanitation DistrictSeptember 2002 Arber Low 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

Cortez Sanitation DistrictSeptember 2002 Arber Low Pressure / High Intensity (Selected) Disadvantages –Relatively Short Track Record Compared to Low/Low and Medium –More Lamps Required than Medium

Cortez Sanitation DistrictSeptember 2002 Arber Specifying UV Dose EPA UVDIS Computer Model BioAssay Performance Based

Cortez Sanitation DistrictSeptember 2002 Arber UVDIS Computer Model Advantages –Computer program easy and fast to run –Theoretical model developed by EPA

Cortez Sanitation DistrictSeptember 2002 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

Cortez Sanitation DistrictSeptember 2002 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

Cortez Sanitation DistrictSeptember 2002 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

Cortez Sanitation DistrictSeptember 2002 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

Cortez Sanitation DistrictSeptember 2002 Arber Performance Based Disadvantages –Relying on manufacturers to design adequate system –Must determine a method to check performance in the field

Cortez Sanitation DistrictSeptember 2002 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/cm 2 based on UVDIS

Cortez Sanitation DistrictSeptember 2002 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

Cortez Sanitation DistrictSeptember 2002 Arber Comparison of UV Systems Mfr AMfr B # of Lamps4864 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

Cortez Sanitation DistrictSeptember 2002 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

Cortez Sanitation DistrictSeptember 2002 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

Cortez Sanitation DistrictSeptember 2002 Arber Transmissivity Adjustment Adjust UV system output based on correlation between design UVT and actual UVT

Cortez Sanitation DistrictSeptember 2002 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

Cortez Sanitation DistrictSeptember 2002 Arber Cortez 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

Cortez Sanitation DistrictSeptember 2002 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