UV (Ultraviolet Light) Wastewater Disinfection – Design, Installation & Life Cycle Costs

www.ablewright.com

By Doug Mitch / Able Wright, Inc.

UV disinfection systems must be properly designed to insure a successful installation & reliable operation. The following summary addresses the different types of UV systems available, design and installation issues, and a checklist with life cycle cost considerations…

Why Use UV ???

Advantages…

• Environmentally friendly

• Effective on a wide range of microorganisms

• Simple to operate; Low maintenance costs

• Chemical free - No disinfection byproducts

• No flavor, odor or physical effects

• Very short contact time requirements

• No possibility of over dosing

• Applicable to potable water or wastewater

• Non-corrosive

Types of UV Lamps:

1. Low Pressure (40W – 100W)

2. Low Pressure High Output (160W – 1,000W)

3. Medium Pressure (400W – 20,000W)

Low Pressure Lamps

• 40 to 100 Watt output, typically

• Supply voltage: 120V or 240V

• Internal gas pressure between 10-2 and 10-3 Torr

• Lamp surface temperature 110 deg F

• Monochromatic UV Output (254 nm)

• Operate most efficiently at water temperature of approximately 60 deg F

Low Pressure, High Output Lamps

• 160 to 1,000 Watt output, typically

• Supply voltage: 120V or 240V

• Internal gas pressure between 10-2 and 10-3 Torr

• Lamp surface temperature 110 deg F

• Monochromatic UV output (254 nm)

• Operate most efficiently at water temperature of greater than 60 deg F

Medium Pressure UV Lamps

• 400 to 20,000 Watt output, typically

• Supply voltage: 230V and 480V

• Internal gas pressure between 102 and 104 Torr (nearly atmospheric)

• Lamp surface temperature 1500 deg F

• Polychromatic UV output (220 to 320 nm)

• Efficient at any water temperature

• Broader range of germicidal effectiveness

UV Wastewater Design Considerations:

• Design for peak flow and provide adequate unit redundancy

• Provide proper pre-screening & outlet control. (No twigs, debris, muskrats, etc.)

• Locate UV unit with ample service access. Provide sufficient floor space.

• Integration with SCADA system? Presentation of critical alarms ?

• Consider quartz sleeve cleaning requirements - essential for proper performance

• Automate cleaning, whenever possible - make it operator friendly

• Utilize a flow meter and auto lamp power level control to economize on power costs

• Install a Transmittance Sampler/Analyzer for real time UVT instrumentation

• Maintain 36" clearance from front of electrical panels, per National Electrical Code

• Provide sanitary microbiological sampling points close to the UV unit

• Keep adequate spare parts on hand for prompt replacements

Installation Issues

Open Channel Systems:

• Insure proper level control for lamp submergence at varying flowrates (weirs, gates, etc.)

• Provide adequate floor space and handling equipment for rack removal, chemical cleaning of quartz sleeves, etc. including: overhead hoist, cleaning trough/bench, & Operator personal protective equipment

• Utilize UV eye protection measures to prevent accidental UV exposure

Installation Issues

Closed Vessel Systems:

• Keep the lamps fully submerged during operation – no partial flow, no air

• Provide proper air and vacuum release in the piping system

• Consider ventilation, condensation, flood prevention, and weather protection issues

Life Cycle Cost Analysis Checklist:

Viable UV equipment alternatives should be evaluated on a life cycle cost basis, considering the following…

1. UV Equipment Capital Cost… (Design Life 20 years)

• Primary Unit(s)

• Redundant Unit(s)

2. Facility Cost Allocation…

• $ / SF Building Cost, prorata share

• Special Support Equipment

Hoisting equipment, access, etc.

Pumping equipment

3. Electrical Power Costs…

• Average Lamp Power (KW) X Number of Lamps X Operating Hrs / Year= Annual Power Consumption (KW-Hrs)

• Annual Power Consumption (KW-Hrs) X Power Cost ($ / KW-Hr)= Annual Power Cost ($)

Power Costs: currently range $0.05 to $0.20 / KW-Hr nationwide.

4. Replacement Parts…

• Lamps - 4,000 to 12,000 Hr typical advertised life

• Ballasts - 1 to 5 year life range

• Solid State Transformers – 10 to 20 year life

• Quartz Sleeves - 2 to 5 year life range

• Sleeve Seals - 2 to 5 year life range

• Wiper Rings - 1 to 2 year life range

5. Labor Costs…

• Sleeve Cleaning

Manual chemical cleaning, or

Automated mechanical wiper

• Replacement Parts

UV Lamps

Ballasts

Quartz Sleeves

Wiper Rings

6. Misc. Expenses…

• Cleaning chemicals & associated supplies

• PPE: UV face shield, eye protection, gloves, aprons, etc.

• UV monitor calibration

• Microbiological sampling

Engineers & Operators: If we can be of assistance to you during design of a UV disinfection application – give us a call. We offer design assistance, technical field service and prompt delivery of spare part kits & replacement components for UV disinfection equipment, as well as coordination of factory rebuilds.

Contact us at:

Able Wright, Inc.

PO Box 849

Plains, MT 59859

(406)250-8389

www.ablewright.com

AbleWright@blackfoot.net

Doug Mitch is the founder and President of Able Wright, Inc. – a provider of water treatment equipment and technical services, specializing in disinfection and chemical feed applications in Montana, Wyoming, Idaho, and Washington. www.AbleWright.com