ENVE 436

UV/OZONE/PEROXIDE TREATMENT



 
 
 

Group Members:  Jeffrey Clarin
Martin Fletcher
Donna Reichardt


The first use of ozone was in 1906 in France. It was used as an oxidizing agent to disinfect water. After 70 years of advancement in wastewater treatment technology, the synergistic effects of UV light, ozone, and hydrogen peroxide were finally discovered in 1976. During the years before this finding, technology was created combining ultraviolet light (UV) with ozone and UV with hydrogen peroxide. Following the discovery of treatment technology combining these three components, Ultrox International of Santa Ana, California built a system to treat wastewater using UV, ozone, and peroxide in 1984 (1).

UV/Ozone/Peroxide treatment is an ultraviolet radiation and oxidation technology. As the name implies UV/Ozone/Peroxide treatment is comprised of three individual components: ultraviolet radiation, ozone gas, and hydrogen peroxide solution. The components together use radiation and chemical oxidation to disinfect and destroy a wide range of contaminants. To understand how the UV/Ozone/Peroxide treatment works it is necessary to understand the individual components. Together ozone and hydrogen peroxide comprise the chemical oxidation aspect of UV/Ozone/Peroxide treatment while ultraviolet light makes up the radiation aspect.


CHEMICAL OXIDATION

Chemical oxidation is a process by which compounds, such as waste products are oxidized to a more environmentally benign state. Waste products that can be destroyed by oxidation include organic molecules, chlorinated VOCs, mercaptans, phenols, and some inorganics. Cyanide (NaCN) is one such product, which can be oxidized in the presence of ozone to a safer state (2):

O3 + NaCN --> NaCNO + O2

Oxidation and reduction equations occur in pairs to make up an overall redox equation. The governing factor behind oxidation is the standard electrode potentials of the chemicals involved. Chemicals, which have high positive values for electrode potential, such as hydrogen peroxide and ozone, spontaneously react with other chemicals. Ozone is commonly used in water and wastewater applications as a disinfectant because it is a powerful oxidant, and reacts with most toxic organics. Ozone reacts with organic molecules in many ways: inserting an oxygen into a benzene ring, breaking double bonds to form aldehydes and ketones, reacting with alcohol to form organic acids (2).

Hydrogen peroxide is used to treat liquid and solid hazardous wastes because it readily reacts with organic chemicals to form carbon dioxide and water. Chemicals that are reactive with hydrogen peroxide are as follows: nitriles, aldehydes, alcohols, amines, metals, alkylboranes, azo-compounds, cyanides, phenols, sulfides, and chromium (1). But, it is not necessarily hydrogen peroxide or ozone which reacts with a reducing agent. Ozone decomposes in a solution of water and hydrogen peroxide decomposes in the presence of an iron catalyst to create a large number of hydroxyl radicals (OH-). It is the hydroxyl radicals that react with compounds at a much higher rate than the parent compound. Another way to enhance the oxidation reactions for both ozone and hydrogen peroxide is through the use of ultraviolet radiation.


RADIATION

Radiation is a process by which energy is transferred from one location to another. One such form of radiation is ultraviolet light. Ultraviolet light is often used as a disinfectant in water and wastewater treatment. Radiation in high doses can permanently damage the building blocks of life. It is with this method that ultraviolet light is used to kill microorganisms and disinfect water. Ultraviolet radiation is powerful enough to break many covalent bonds. Alone it can degrade PCBs, dioxins, polyaromatic compounds, and BTEX (1). UV light has another affect; it enhances chemical oxidation. The way ultraviolet light enhances chemical oxidation is somewhat of mystery. One theory is that organic compounds absorb light energy at visible or ultraviolet wavelengths and as a result are easier to destroy. In short, UV/Ozone/Peroxide treatment is combination of the above technologies. In combining several oxidation methods with a source of radiation energy, the limitations of the individual components are reduced.

A full scale UV/Ozone/Peroxide treatment system treats contaminated groundwater, industrial wastewater, and leachates containing chemicals such as: halogenated solvents, phenol, pentachlorophenol, pesticides, PCB's, explosives, BTEX, MTBE, and many other organic compounds. The UV radiation and oxidation system consists of a UV/Oxidation reactor, an air compressor with an ozone generator module, and a hydrogen peroxide feed system. A common UV/Ozone/Peroxide process is shown below in Figure 1(3):

Figure 1: UV/Ozone/Peroxide Process Schematic
 


ADVANTAGES

The advantages of a treatment process using ultraviolet light, ozone, and hydrogen peroxide are numerous. The first one involves the actual treatment technology. A UV/Ozone/Peroxide system is a destruction process, and the final products are only carbon dioxide, water, and inert salts (4,5). Therefore, the process residuals do not require any additional treatment, as they might in conventional systems.

In the UV/Ozone/Peroxide process, ozone is used as an oxidant, instead of the more conventional use of chlorine. Ozone is a better disinfectant than chlorine and is not known to produce toxic or mutagenic substances (1). Also, because ozone must be generated on site and used immediately, no storage area is required for the oxidant (6).

The costs involved with the UV/Ozone/Peroxide process are lower than the costs for a system utilizing only ultraviolet light and ozone, because the addition of hydrogen peroxide allows the use of a smaller ozone generator and less oxidants (1). Also, the residence times needed to decrease the concentration of a contaminant to a certain level are lower for the UV/Ozone/Peroxide system than for ozone alone, UV/Ozone, or UV/Peroxide processes (2).

The final advantage of this treatment technology is the wide variety of contaminants and concentrations that can be treated. The limitations of ultraviolet light, ozone, and hydrogen peroxide alone are overcome by combining the three constituents. Finally, the oxidants and the Ultrox International system are becoming readily available (1,4).
 


DISADVANTAGES

There are still a few limitations and dangers involved with the UV/Ozone/Peroxide treatment technology. High turbidity, solid particles, and heavy metal ions in the aqueous stream are all interferences that reduce the effectiveness of the treatment (4). Because these substances must be removed to ensure good treatment, the aqueous stream may need pretreatment.

Unfortunately, the equipment needed for this new treatment process can be expensive and require a large amount of space. The energy required for the process is high resulting in large costs (1,4). Also, capital costs are higher for the UV/Ozone/Peroxide system than for conventional systems, but operating costs are lower (1). Ozone can also be costly, because it must be generated and immediately applied at the treatment location (2). Finally, large areas are needed for the many ultraviolet lamps required in this process (5).

Each of the constituents in the UV/Ozone/Peroxide process has dangers. Ozone is explosive, toxic, and an irritant to the skin, eyes, respiratory tract, and mucous membrane (7). Hydrogen peroxide is an irritant, can cause chemical burns, and is an explosive hazard (1). Ultraviolet light can burn unprotected skin and the mercury in UV lamps can damage the central nervous system, along with inflaming the nose and throat area (4).

Ozone is also a significant air pollutant and monitoring must be completed to ensure that ozone levels are not exceeding regulatory concentrations (2). Lastly, the UV/Ozone/Peroxide process mechanisms are still not totally understood.
 
 


CASE STUDY(8)

In developing any new treatment technology, case studies are a must in determining their capability of treating a contaminant. One of the first case studies for UV/Ozone/Peroxide treatment was done for the US Department of Energy Kansas City Plant (KCP) in Kansas City, Missouri. The main source of contamination was volatile organic compounds (VOCs) and the identified surrogate chemicals were PCE, TCE, 1,2-DCEs and Vinyl Chloride. The field application used was a pump and treat system that extracted contaminated groundwater for remediation. The remediation treatment was through advanced oxidation processes (AOP), using a UV/Ozone/Peroxide treatment system, which ran from May 1988 to May 1993. When the UV/Ozone/Peroxide system was initiated in 1988, it was one of the first full-scale operating AOP of its kind. For the first 4 years, close monitoring of the treatment system to develop pilot studies to verify this new treatment was performed for regulators to see. At the end of the 4 years, an improved UV/Peroxide system was implemented (currently on going) from the previous 4-year pilot study and is shown below in Figure 2:


Figure 2: Modified UV/Peroxide Treatment Schematic



The results below illustrate the effectiveness of the treatment at the KCP site:

Table 1: Final Concentrations of the KCP UV/Ozone/Peroxide Treatment Process

Treatment Process
Contaminant
Influent Contaminant Concentration, m g/l
Effluent Contaminant Concentration, m g/l
Percent Removal
Percent Detected in Ambient Air
Percent Detected in Sewer Discharge
             
Initial UV/O3/H2O2
VOCs
-
-
@ 94.6%
@ 3.7%
@ 1.7%
Modified UV/ H2O2
VOCs
-
-
>99.95%
0.00 %
<0.05%
Modified UV/ /H2O2
PCB
0.3
0.0
100 %
0.00%
0.00%

 

Based on these results the use of the UV/Ozone/Peroxide, especially the modified UV/Peroxide system, proved an effective process for removing and containing VOC contamination in the groundwater. The system was designed to treat 30,000 m g/l and the average influent was 25,00 m g/l. Along with the high contaminant removal, the system design conditions were met. The modified UV/Peroxide process replaced the UV/Ozone/Peroxide system, because the initial system, containing ozone, required lots of maintenance on the ozone generator and the delivery system. Ozone leaks were discovered (causing downtime) and the residual ozone proved to be corrosive in the reaction chamber. Several other improvements were made to the initial UV/Ozone/Peroxide process because serious downtime was encountered for acid cleaning of the filters, UV lamp sheathes, and ozone sparger tubes. The modified system took this into account and added a pH adjustment before the UV/Peroxide treatment and therefore lessened the chance of fouling due to the oxidation of organics.

Overall, the research procedure was deemed very useful. An initial design was tested, and based on the results a modified system was implemented, which is the whole basis of research. The initial UV/Ozone/Peroxide demonstration system served as a stepping stone in developing the modified UV/Peroxide process and clearly treated the saturated hydrocarbon contamination.

As with most ex-situ treatment processes, especially pump and treat methods, much of the VOC mass is removed from the subsurface and treated with UV/Peroxide or UV/Ozone/Peroxide, but there is still some in-situ groundwater VOC concentrations that will remain untreated. This therefore limits most ultraviolet treatment systems, unless improved extraction procedures are utilized.


FUTURE CONSIDERATIONS

The future of this treatment technology includes continuing to learn more about the process and how to improve it. Higher intensity ultraviolet lamps are already being produced to reduce the space and cost requirements for this process (5). Another innovation currently being studied is a way to reduce the number of solid particles in the aqueous stream, so the amount of UV light reaching the particles is greater. An electron-beam accelerator can be used to "zap" the aqueous stream and oxidize organic contaminants to form harmless substances, like carbon dioxide and salts (8). The UV/Ozone/Peroxide treatment technology is still new and advances are constantly being discovered to improve the process.


REFERENCES CITED

1. O’Brien & Gere Engineers, Inc. Innovative Engineering Technologies for Hazardous Waste Remediation. New York: Van Nostrand Reinhold; 1995.

2. LaGrega, M.; Buckingham, P.; Evans, J. Hazardous Waste Management. New York: McGraw-Hill, Inc.; 1994.

3. U.S. Filter/Zimpro, Inc. (Ultraviolet Radiation and Oxygen).
http://clu- in.com/site/complete/democomp/usfilzim.htm

4. Ultraviolet (UV) Oxidation. http://www.frtr.gov/matrix2/section4/4_56.html

5. Chin, K.; Fouhy, K.; Kamiya, T. Chemical Engineering. "Advanced Oxidation Mission: Search and Destroy;" July 1997.

6. Encyclopedia of Environmental Science and Engineering. 3rd edition. Vol. 2. Philadelphia: Gordon and Breach Science Publishers; 1992.

7. The New Encyclopedia Britannica. 15th edition. Vol. 2. Chicago: Encyclopedia Britannica, Inc.; 1998.

8. Pump and Treat of Contaminated Groundwater at U.S. Department of Energy, Kansas City Plant, Kansas City, Missouri.
http://denix.cecer.army.mil/denix/library/Remedy/Kansas/ksplnt02.html

9. Black, P. Business Week. "Zapping Toxic Waste with 1.5 Million Volts," February 3, 1992.
 
 

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