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Wastewater Treatment Plants & Bacteria: Strategies for Compliance UV Systems ; Alternative Disinfectant to Free Chlorine Harris County Wastewater Symposium.

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Presentation on theme: "Wastewater Treatment Plants & Bacteria: Strategies for Compliance UV Systems ; Alternative Disinfectant to Free Chlorine Harris County Wastewater Symposium."— Presentation transcript:

1 Wastewater Treatment Plants & Bacteria: Strategies for Compliance UV Systems ; Alternative Disinfectant to Free Chlorine Harris County Wastewater Symposium Wastewater Treatment Plants & Bacteria: Strategies for Compliance Tim Brodeur, PE April 26, 2011

2 Wastewater Treatment Plants & Bacteria: Strategies for Compliance UV Disinfection – Basic Concept Chemical Disinfection UV Disinfection milligrams*min/Liter millijoules/cm 2 (mJ/cm 2 ) CT IT Concentration (mg/L) x Intensity (mW/cm 2 ) x Contact Time (minutes) Contact Time (sec)

3 Wastewater Treatment Plants & Bacteria: Strategies for Compliance UV Principles Germicidal portion of UV radiation band is between nm in the UV-range (short wave). Hg vapor lamps are charged by striking to produce an electric arc. Emitted light is UV light. 3 categories for UV Disinfection Systems: – Low-pressure low intensity – Low-pressure high intensity – Medium-pressure high intensity

4 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Germicidal Effectiveness of UV Radiation UV light is physical rather than chemical disinfecting agent – penetrates the cell wall and is absorbed by nucleic acids, which either kills cells or prevents replication (RNA interference) Variables affecting performance: – Characteristics of UV disinfection system – Overall system hydraulics – Presence of particles – Characteristics of the micro organisms – Chemical characteristics of the wastewater

5 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Closed Channel & Open Channel Reactors Drinking Water Re-UseWastewater Racine, WI UV System (100 mgd peak) WSSC Laurel, MD UV System (120 mgd )

6 Wastewater Treatment Plants & Bacteria: Strategies for Compliance UV Disinfection System Components & Configurations UV lamps Quartz sleeves holding UV lamp Supporting structure for UV lamps/quartz sleeves Ballasts used to supply regulated power to lamps (limit current to a lamp) Power supply

7 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Upstream solids removal process has large impact on UV system sizing and cost Upstream Solids Removal Process Design UVT (%) Design UV Dose (mJ/cm 2 ) Granular Media MF/UF membranes 6580 RO 9050 Florida/NWRI HLD requirements Increasing Filtration Cost Increasing UV Cost UV transmittance (UVT)

8 Wastewater Treatment Plants & Bacteria: Strategies for Compliance UV Open Channel Disinfection Systems Design flow rate is divided among a number of open channels with two or more banks of UV lamps in series. Need stand-by bank for system reliability. Includes flow control or weighted flap gate to keep lamps submerged. Lamps need to be periodically removed to clean – prevent fouling. Mechanical cleaning systems are used with low-pressure high-intensity system to avoid fouling of quartz sleeves.

9 Wastewater Treatment Plants & Bacteria: Strategies for Compliance UV Open Channel Systems

10 Wastewater Treatment Plants & Bacteria: Strategies for Compliance UV Closed Systems Direction of flow is perpendicular to placement of lamps Some systems do have flow parallel to lamps Also fixed geometry arrangements – medium pressure. Vendors Calgon Trojan WEDECO Aquionics Siemens Atlantium Ozonia Severn Trent

11 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Definition of UV Dose (D) D = I x T where: D = dose, mJ/cm 2 (= m W.s/cm 2 ) I = UV intensity (mW/cm 2 ) T = exposure time, seconds, s D is analogous to chlorine disinfection (C R t)

12 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Problems with UV Applications Inaccurate knowledge of the UV intensity. Exposure time associated with all of the pathogens passing through a UV disinfection system. Open channels – achieving a uniform velocity field in the approach and exit channel. Especially difficult is when UV is retrofitted into existing open channel (converted chlorine contact chambers). “UV Disinfection Guidelines for Drinking Water and Wastewater Reclamation” (NWRI and AWWARF, 2000).

13 Wastewater Treatment Plants & Bacteria: Strategies for Compliance Questions ? Tim Brodeur, PE

14 UV offers simple operations and small footprint Atlanta UV System (180 mgd) Boston UV System (450 mgd) Rahway, NJ (85 mgd) Vendors Calgon Trojan WEDECO Ozonia Aquionics Siemens Atlantium Severn Trent


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