United States Environmental Protection Agency EPA/540/F-93/501 March 1993 &EPA SUPERFUND INNOMTM TECHNOLOGY EVALUATION Emerging Technology Bulletin Destruction of Organic Contaminants in Air Using Advanced Ultraviolet Flashlamps Purus, Inc. Technology Description: This technology uses photolytic oxi- dation to destroy volatile organic compounds (VOCs) in soils and groundwater. The system uses a xenon pulsed-plasma flashlamp that emits short wavelength ultraviolet (UV) light at very high intensities. The process strips the contaminants into the vapor phase, where the UV treatment converts the VOCs into less hazardous compounds. (See figure 1) Direct photolysis does not form hydroxyl radicals. Direct photoly- sis occurs when the contaminants absorb sufficient UV light energy, transforming electrons to higher energy states and break- ing molecular bonds. The process requires the UV light source to emit wavelengths in the regions absorbed by the contaminant. An innovative feature of this technology is the ability to shift the UV spectral output to optimize the photolysis. The process uses vacuum extraction or air stripping to volatilize VOCs from soils or groundwater, respectively. VOCs then enter the photolysis reactor, where a xenon flashlamp generates UV light. T~he plasma is produced by pulse discharge of electrical energy across two electrodes in the lamp. Ninety-nine % destruc- tion of the contaminants occurs within seconds, allowing echinu- s'0" Power Supply and Electronics Septum Sampling Port Air Out Septum Sampling Port TCE Booster Metering Valve Air In Impingers Flow Meters Air Pump Figure 1. Schematic of Air-2 photochemical reactor. ------- oos operation. Because organlcs are destroyed in the vapor phase, the process uses less energy than a system treating dissolved crgnnfcs, Waste Applicability: The Purus, inc. photolytic oxidation pro- cess Is designed to destroy VOGs, Including dichioroethylene (DCE), t»!rachtoroethyiene (PCE), trtchtaroethylene (TOE), and vinyl chlorMe volatilized from soil or groundwater. Other VOCs, such as hanzene, carbon tetrachforkte, and 1,1,1-trichIoroethane, «r» being Investigated. Teat Resullst A fuB-scale field test began fn October, 1991, and W@® completed fn July, 1992, The results are listed in table 1. The test was conducted at the Lawrence Livermore National Labora- tory Superfiirtd site 300r about 15 miles east of Livermore, GA. Th® «h« contains soil zones highly contaminated with TCE. A vacuum extraction system delivered contaminated air to the Purus Unit at air Hows of up to 500 cubic feet per minute (cfm). Initial ooncenfraUons of TCE in the air were approximately 250 parts per million by volume. The contaminant removal goal for the treat- ment was 99%. Vapor phase carbon filters were placed down- stream of the Purus unit to comply with the California Air Quality ©mmtesforts control standards during the field test. The low-wavelength UV emissions allowed direct photolysis of many VOCs, particularly chlorinated compounds and freons, that would not have been possible with commercial mercury lamps. Very rapid and efficient destruction was observed for TCE, PCE, and DCE, Some VOCs required either pholo-sensitizatfon or a lower-wavelength light source for rapid photolysis. The TGE removal resulted in undesirable intermediates. The main product (greater than 85%) from the chain photo-oxidation of TCE is dichloraacetyl chloride (DCAG). Further oxidation of DCAO is about 100 times slower than the photolysis of TCE and forms dichloroeaibonyl (DOG) fn about 20% yield. At this level of treatment, the DGC concentration may be excessive, requiring additional treatment Further studies should focus on the effec- tiveness of dry or wet scrubbers for removing acidic photo- oxMatfon products, developing thermal or other methods for post-treatment of products, and examing the use of shorter- Wavelength UV lamps or catalysis, to treat a broader range of VOCs, Parus will examine several of these issues with Argonne National Laboratory in continued demonstrations at the Depart- ment of Energy Savannah River site. A paper and project summary have been submitted for printing and will be available in the near future. T*&f* 1. Suttwaty o/ Field Resute with tfta Air-3 Photoreacior* No, of tfss, TOE CMorfna SJXW Time Dostfuctton Mote % Mole % Mote % Balance Lamps fsac/ #y DOC* DGA&* C{- m 30 30 m 16 m s & 1 i 4 4 4 2 4 2 4 2 4 S &,& 10,1 10,4 4.6 1O,i 4,8 10.4 4,8 9,3 4,S £99,89 &3&S9 £99.99 99.92 ZS9.99 299.99 L-99.93 fesass 9B.16 88,57 ndf 19.6 2&.O 17.3 21.8 12.4 8.3 9.3 12.3 6,9 25.8 24.4 34.6 S3.7 nd 64.5 72.2 75.2 91.8 86.2 61.6 89.9 91.4 65.3 682 43.2 41.9 38.6 35.8 35.8 78.8 106.2 114.5 91.1 nd 86.2 90.0 88.8 90.3 93.3 Dictihtoaegtyl efcfo/Jefe * Not detected* *Dkhlorocarbonyl(phosgene). For Further Information:: EPA Project Manager: Norma M. Lewis U.S. EPA Risk Reduction Engineering Laboratory 26 West Martin Luther King Drive Cincinnati, OH 45268 (513) 569-7685 FAX (513) 569-7620 Technology Developer Contact: Paul Blystone Purus, inc. 2150 Paragon Dr. San Jose, CA 95131 (408) 453-7804 FAX (408) 453-7988 Untied States Environmental Protection Agency Center for Environmental Research Information Cincinnati, OH 45268 Official Business Panaliy for Private Use $300 BULK RATE POSTAGES FEES PAID EPA PERMIT Mo. G-35 ------- |