Rich Stummer Daman Superior LLC UltraTech UV Systems UV Topics - PowerPoint PPT Presentation

Rich Stummer Daman Superior LLC UltraTech UV Systems

UV Topics  History of UV  Types of UV Systems  How does UV Disinfect Wastewater  UV vs Other Disinfectant Systems  Components of UV Systems  Advantages & Disadvantages  Design Considerations  Maintenance of Systems

History of UV  in 1878 discovered that sunlight kills microbes in broth.  In 1904, the first quartz lamp was developed  In 1910, the first UV system used to disinfect drinking water  1938 Westinghouse Electric introduced the fluorescent gas discharge tube  1940’s lamps and ballasts improved  Late 1970’s, US EPA discouraged use of chlorine

History of UV (continued) • Late 1970’s, US EPA started funding research and grants for UV systems • 1978, full scale UV system for wastewater successfully demonstrated at NW Bergen WWTP (Waldwick, NJ) • 1982, modular UV system for open channel to disinfect wastewater introduced (gravity fed system with lamps parallel to flow (horizontal) • Use of UV for wastewater growing since 1982

A survey in 2003 by the Water Environment Federation showed that of all the respondents , 24% used UV disinfection in their wastewater treatment plants and 66 % were planning to switch to UV (Water Environment Federation 2004)

UV Systems – Early Designs  Problems with early systems  Replacement of bulbs, sleeves & ballasts required shut down of system  Poor cleaning systems  Poor/inadequate hydraulics – short circuiting  Improper cooling of ballasts – failures  Ballasts & lamps not matched – lamp failures  Difficulties in maintenance  Lack of scientific knowledge to properly size UV systems for wastewater

UV Patents  1972, A. Landry issued patent for water flow through teflon tube, UV lamps surrounded tube  1978, S. Ellner issued patent using rectangular, gravity flow chamber with lamps perpendicular to flow with in-place chemical cleaning and UV sensors (installed in Suffern WWTP, Suffern, NY – still in use toady)  Numerous patents since on design and features for UV systems

Types of UV Systems  Closed Channel UV System

Types of UV Systems  Open Channel Vertical System

Sample Design – Vertical Modular System 60 “ Water Depth 28 Lamp 16” or 20” Wide Modules 40 Lamp 24” Wide Modules High Output UV Lamps or Long Life Standard Intensity Lamps Air Scrub Cleaning Mechanical Wiper Cleaning Chemical Cleaning (optional)

How Does UV Disinfect?  UV light part of electromagnetic spectrum  Radiation with wavelengths between 30 and 400 nanometers (nm)  Shorter wavelengths than visible light  Sometimes referred to as “black light” – can not be seen by human eye  UV spectrum divided into 3 parts  UV-A (315 – 400 nm)  UV-B (280 – 315 nm)  UV-C (200 – 280 nm) (UV output 254nm)

How Does UV Disinfect  Transfer of electromagnetic energy from mercury arc lamp to organisms genetic material (DNA and RNA)  UV penetrates cell wall and destroys cell ability to reproduce  Organisms can’t reproduce and eventually die off

How Does UV Disinfect  Wavelengths of UV  UV-A 315 – 400 nm  UV- B 280 – 315 nm  UV - C 200 – 280 nm  Optimum wavelength to effectively inactivate microorganisms is range of 250 – 270 nm (UV – C)

Methods of Disinfection  Chlorination – different forms  Chlorine gas  Chlorine dioxide  Sodium Hypochlorite  Calcium Hypochlorite  Ozone – Gas  Ultraviolet Light – UV Radiation

Chlorination  Special handling and storage requirements  De-chlorination required  Low equipment costs  Corrosive  Toxic  Formation of carcinogenic by-products (trihalomethanes)  Requires chemical feed system  Effectiveness depends on water quality

Ozone  Strong oxidizer, non-selective  Highest equipment costs  Short life span but still requires neutralization  Corrosive  Toxic  Requires feed gas and injection system  Effectiveness depends on water quality  High output systems require ozone off gas destruction

Ultraviolet  No special handling  No post treatment  Moderate equipment costs  Frequent preventative maintenance cycles  Fouling can reduce effectiveness  Performance dependant on water quality

Low-Pressure vs Medium Pressure Lamps  Low-Pressure Lamps  Wavelength of 253.7 nm  Lengths of 0.75 and 1.5 meters with diameter of 1.5 – 2.0 cm.  Medium-Pressure Lamps  15-20 times germicidal UV intensity of low-pressure lamps  Disinfect faster  Greater penetration capacity  Operate at higher temperatures; higher energy consumption

Components of UV System  Mercury Arc Lamps – pressure refers to pressure inside lamps; intensity refers to energy output  Low-pressure Low-intensity (lp-li)  Low-pressure High-intensity (lp-hi)  Medium-pressure High-intensity (mp-hi)  Reactor  Ballasts

Low-Pressure Low-Intensity Lamps  Most energy efficient for UV disinfection  Operating temperature is 40 – 60 degrees Celsius  Lamps contain mercury vapor and argon gas  Emits nearly monochromatic radiation  About 85% of emissions are at 253.7nm – peak germicidal effectiveness  Emit approximately 0.2 germicidal watts per centimeter arc length (W/cm)

Low-pressure High intensity  Operating temperature of 180 – 200 degrees celsius  Emits broader, polychromatic radiation therefore less efficient than lp-li  High-intensity = higher capacity : requires fewer lamps  Germicidal output 13 W/cm  Lamp costs 3+ times cost of lp-li

High-pressure High intensity  Operating temperature of 600 – 800 degrees celcius  Emits broader, polychromatic radiation therefore less efficient than lp-li  High-intensity = higher capacity : requires fewer lamps  Germicidal output 16 W/cm  Lamp costs 5 times cost of lp-li  Power costs about 4 times higher than lp-hi

High-intensity or Low-intensity  Low-intensity best suited for smaller systems  High-intensity best suited for larger systems  Example : Southtowns WWTP 16 MGD  The lp-li system is not considered cost effective at the large flow rates experienced at the Southtowns WWTP because of the number of lamps required. The lp-li alternatives would require approximately 2,160 lamps, while the lp-hi system would need 360 lamps (6 times less) and the mp-hi alternative would need 176 lamps (12 times less).

Horizontal UV System  Utilized when channel depth too shallow for vertical system  Electrical connections under water  Disinfecting area limited to arc length of UV lamp  Rack must be removed from channel and underwater seal disassembled to change UV lamp  Lamp change takes 10 minutes

Vertical UV System  Requires channel depth of at least 60”  All electrical connections above water  Flow perpendicular – area of UV energy expanded  Lamps changed without removing module from channel  Lamp change takes 15 seconds

Example  UV System with 300 lamps  Horizontal system would take 50 hours of labor to change lamps  Vertical system would take 1 hour and 25 minutes to change lamps

UV Dosage Comparison  UV Dosage is a function of the UV Intensity times the Contact Time  Engineer should require suppliers to provide  UV output of specific lamp  Number of UV lamps  Contact time at maximum flow rate  (# of UV lamps) x (UV output) = Total UV watts in system  (Total UV watts) x (contact time) = UV Watt Seconds

EXAMPLE  Mfg X proposes 98 UV lamps  Output of 65 watts (at 254nm)  Contact time of 12 seconds  98 x 65 =6,370  6,370 x 12 = 76,440  This system rates at 76,440 watt seconds  Contact Time is cheaper than Intensity  Since no harm in over dosing, design of 2-3 times minimum dose is common

Understanding UV Disinfection  Terms  Ultraviolet Dose  Collimated Beam Test  UV Lamp Life  UV Lamp Description  UV Lamp Comparisons

Ultraviolet Dose  UV Dose = Intensity x Time expressed in uWattseconds/cm2, Mwattseconds/cm2 or Jewels  Problem – UV Transmittance of effluent impact on true UV dose; “average” UV intensity; “average” contact time; hydraulics  Solution – Bioassay – performance based validation (Delivered Dose is actual dose received by targeted organism)

Collimated Beam Test  Test conducted with MS2 phage in solutions of effluent will indicate the additional contact time to achieve specific levels of disinfection  Does not provide information relating to actual UV dose

UV Lamp Life  UV lamps will continue to provide the same amount of visible light after the germicidal output has diminished below safe disinfecting levels (solarization of the lamp glass)  Effective Lamp Life – where UV output has diminished to 70% of the new lamp output after 100 hours of operation  Lamp Life is not the number of hours of operation until the lamp goes out