Ultraviolet Radiation And Oxidation For Groundwater Decontamination

This ultraviolet (UV) radiation and oxidation process uses UV radiation, ozone, and hydrogen peroxide to destroy toxic organic compounds, particularly chlorinated hydrocarbons, in contaminated groundwater. The process oxidizes compounds that are toxic or refractory (resistant to biological oxidation) to parts per million (ppm) or parts per billion (ppb) levels.

The UV radiation and oxidation system (Fig. 11) consists of a treatment tank module, an air compressor and ozone generator module, and a hydrogen peroxide feed system. The system can be skid-mounted and portable, and may permit onsite treatment of a wide variety of liquid wastes, such as industrial wastewater, groundwater, and leachate. Treatment tank size is determined by the expected wastewater flow rate and the necessary hydraulic retention time needed to treat the contaminated water. The approximate UV intensity, and ozone and hydrogen peroxide doses, are determined by pilot-scale studies [61,62].

Treatment tank influent is simultaneously exposed to UV radiation, ozone, and hydrogen peroxide to oxidize the organic compounds. Off-gas from the treatment tank passes through an ozone destruction unit, which reduces ozone levels before air venting. The ozone destruction unit also destroys VOC stripped off in the treatment tank. Effluent from the treatment tank is tested and analyzed before disposal.

The UV radiation and oxidation system treats contaminated groundwater, industrial wastewaters, and leachates containing halogenated solvents, phenol, penta-chlorophenol, pesticides, polychlorinated biphenyls, explosives, benzene, toluene, ethyl-benzene, xylene, methyl tertiary butyl ether, and other organic compounds. The system also removes low-level total organic compounds, chemical oxygen demand, and biochemical oxygen demand.

A field-scale demonstration was completed in March 1989 at the Lorentz Barrel and Drum Company site in San Jose, CA, United States, under the supervision of the USEPA. The test program was designed to evaluate system performance for several combinations of five operating parameters: (a) influent pH, (b) retention time, (c) ozone dose, (d) hydrogen peroxide dose, and (e) UV radiation intensity [11,12].

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Figure 11 Ultraviolet radiation and chemical oxidation system. (Courtesy of USEPA.)

The UV radiation and oxidation technology is fully commercial, with over 30 systems installed. Flow rates ranging from 5 gallons per minute (gpm) to 1050 gpm are in use at various industries and site remediations, including aerospace, US Department of Energy, US Department of Defense, petroleum, pharmaceutical, automotive, wood-treating, and municipal facilities.

Such UV oxidation technology has been included in Records of Decision for several Superfund sites where groundwater pump-and-treat remediation methods will be used. Contaminated groundwater treated by the system met regulatory standards at the appropriate parameter levels. Out of 44 VOCs in the wastewater, trichloroethene, 1,1-dichloroethane, and 1,1,1-trichloroethane were chosen as indicator parameters. All three are relatively refractory to conventional oxidation.

The ozone destruction unit reduced ozone to less than 0.1 ppm, with efficiencies greater then 99.99%. The VOCs present in the air within the treatment system were not detected after passing through the ozone destruction unit. The UV/oxidation reactor system produced no harmful air emissions. Total organic carbon removal was low, implying partial oxidation of organics without complete conversion to carbon dioxide and water. The UV itself is also an effective chemical reduction process (e.g., dechlorination process) in case the groundwater is contaminated by chlorine or similar oxidizing chemicals [47].

Energy and Environmental Engineering, Inc, East Cambridge, MA, has applied the principles of chemical oxidation, UV radiation, and photocatalysts, and developed a commercial process known as the PhotoCat process. Table 2 shows some representative

Table 2 Removal of Organic Contaminants From Groundwater Using a Peroxide Oxidation-UV Radiation Process

Contaminant

Molecular

Feed concn.

Equivalence

Resistance time

Product

species

weight

(ppm)

ratio

(seconds)

cone C/C0

Chlorobenzene

112

50

3.3

3.7

0.04

Benzene/toluene

78/93

100/100

3.5

3.8

0.4/0.4

Yellow 106

1374

110

4.2

7.7

0.08

Yellow 49

438

110

1.0

23.0

0.007

Blue 41

463

115

0.6

11.5

0.001

Red 83

1025

140

1.0

7.7

0.008

ppm, parts per million by weight. Source: Courtesy of USEPA.

ppm, parts per million by weight. Source: Courtesy of USEPA.

results from groundwater decontamination projects using the UV lamp and hydrogen peroxide system.

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