Results from PCB destruction tests submitted to regulatory officials in Ontario for review in March 1982 are available. "Tests on Aroclor and Askarel with a chlorine content up to 58 percent, show destruction efficiencies in excess of 99.9999 percent with no by-product dioxin detected. These results were corroborated by Laboratory Services of Environment Canada."
References: (Dobson, 1980; EPRI, 1981).
Figure 12 Reaction Vessel Schematic (Royal Military College, March, 1982)
Click image to view a full size version.
4.4.2.3 Catalyzed Microwave Process
Queen's University
Department of Chemistry
Kingston, Ontario
Contact: Dr. J. Wan
613) 547-6180
The catalyzed microwave process for PCB destruction makes use of short duration high energy pulses of microwave energy to activate oxygen and PCB molecules at a metal surface. The molecules react to produce CO2, H2O and a metal chloride.
The key to the process is the metal catalysts. The process is being patented so the exact nature of the catalysts was not disclosed. The catalysts are suspended in a fluid bed fluidized by recirculating pure oxygen or air (two atmospheres). PCBs are introduced into the system and largely remain coating the catalyst surface. Short pulses (<I second) of high energy microwaves (>2 kW) are focused on the catalyst bed. The energy is absorbed at the surface and is transferred to adsorbed O2 and PCB molecules, activating them, and promoting their reaction to the products. There is a pause of 10-15 seconds between pulses so the entire process temperature rises only 10-15°C above ambient. The energy usage was said to be 50% efficient.
The process is in the laboratory evaluation stage. The PCB destruction efficiency observed at this time is >90% based on recovered chloride. The process will be developed further at Queen's University to refine the engineering details. The technology is being developed to recover hydrocarbons from tar sands; as such the engineered units will have to handle solids. Thus the potential for this process to treat solid PCB wastes will be seriously considered.
As this is a very new technology with little work done outside of laboratory studies it is too early to assess environmental impacts and determine regulatory views. Similarly cost and engineering considerations remain to be developed through pilot scale studies.
References: (Spencer, 1982; Wan, pers. comm., 1982).
4.4.2.4 Microwave Plasma Process
Chemistry Research
Lockheed Palo Alto Research Laboratory
Orgn. 52-35, Bldg. 204
3251 Hanover Street
Palo Alto, California 94304
Contact: Dr. E.L. Littauer, Manager
(415) 493-4411
Lockheed has been developing the microwave plasma technology with funding support from the US EPA and the Canadian Electrical Association but the recent funding cut backs have affected these studies. Lockheed has stopped work on the process and does not intend to pursue it on its own.
The Lockheed Microwave Plasma process has been widely discussed in the PCB destruction field. As a result this short note is included for completeness.
Their process involves continuous irradiation and activation of low pressure oxygen (0.1 atm) with microwave energy. PCBs introduced into the radiation zone combine with the active oxygen to produce CO2, HC1 and H2O.
4.4.2.5 Light Activated Reduction of Chemicals (LARC) Process
Atlantic Research Corporation
Alexandria, Virginia
Contact: Judith F. Kitchens
Manager Environmental Sciences
and Engineering Division
Light Activated Reduction of Chemicals (LARC) is a patented (U.S. Pat. 4 144 152) process for the destruction of halogenated organics by ultraviolet light. The process uses UV light in the 1850-4000  region in combination with hydrogen gas to affect the dehalogenation of the chlorinated organic molecules.
Two LARC reactors were used in research; a single lamp tube reactor and a 64-lamp pilot unit. Both reactors contain low pressure UV lamps with 95% of their output at 2537 . The hydrogen gas is introduced into the reactor via 2.0 u fritted stainless steel spargers.
Table 8 Pertinent Reactor Parameters
| |
Tube Unit |
Pilot Unit |
| Number of Lamps |
1 |
64 |
| Capacity |
600 mL |
40 L |
| Light Path Length |
3.33 mm |
6.35 mm |
| Radiant Energy at Lamp Sleeve Surface |
36 300 µW/cm2 |
29 400 µW/cm2 |
| Hydrogen Flow Rate |
0.26 L/min |
1.9 L/min |
| Type of Operation |
- flow through or batch recycle |
- flow through or batch recycle |
The ultraviolet light initiates a photochemical process by homolytic cleavage of the carbon-chlorine bond in the PCB molecule. Optimal conditions to maximize this cleavage and the resultant formation of a carbon-hydrogen bond include the use of shorter wavelength UV, higher temperature and increased hydrogen flow and turbulance. PCBs are fed to the reactor and held for a >20 minute reaction time. The fluid is then analyzed by gas chromatography to determine PCB degradation. The reaction continues until the required dechlorination is met.
The LARC is capable of dechlorinating PCBs, PCB-contaminated waste oil and Aroclors extracted from soil by isopropanol. Degradation products of the LARC process include hydrogen chloride and biphenyl. Large concentrations of biphenyl appear to inhibit the reaction; however, both the hydrogen chloride and biphenyl can be removed by distillation.
In a test involving Aroclor 1254 and 1260 a trend of increasing initial degradation rate with increased chlorination was shown. The pilot unit demonstrated increased degradation over the single lamp reactor due to higher light flux and optimized temperature and flow pattern. These initial rates dropped off over the reaction period due to the formation of biphenyl which competed for the UV. In a commercial process the biphenyl would have to be removed to improve reaction efficiency to greater than the 85% destruction shown in these tests. The tests showed that the maximum initial concentration of PCBs that can be destroyed by this method is 3500 ppm.
Before treatment of PCB-contaminated waste oils can be affected by the LARC process the UV-absorbing oil degradation products in the fluid must be removed. Fuller's Earth or some other chromatographic medium may be used for this purpose. A diluent must then be added to lower the oil viscosity aiding hydrogen gas dispersion in the oil.
Tests were conducted using fluid containing 1000-2000 ppm PCB. All diluents resulted in faster PCB destruction than for PCBs in oil alone. An oil/tetrahydrofuran/isopropanol diluent mixture resulted in the highest initial degradation rate.
The pilot facility is still in its middle stages of development and more testing and feasibility studies are required prior to full scale up. A low to middle level of operator skill can be anticipated due to the simple batch nature of this process, although this technology could become quite sophisticated technically if the operation was continuous.
Costing figures could only be estimated as process descriptions were sketchy and not well defined. Tankage, pumps, conveyor systems, mixers, hopper bins, a distillation column and the reactor itself can be expected to cost just over $1 000 000 if the pilot plant is duplicated for production destruction of PCBs. This figure would include associated piping and instrumentation but no land costs.
Operating costs, again an estimate, would be approximately $1 200 000. Operation at 85% utilization, 24 h/day and 310 days a year, would give an estimated unit cost of $1.38/kg of PCB destroyed.
Further analysis of the LARC process on a commercial scale must be made before an environmental impact assessment can be made.
The process has been patented in the United States and the company is testing on a pilot scale. The process is not yet available commercially and status with the US EPA is unknown.
References: (Kitchens et al., EPRI, 1981).
4.4.2.6 Other UV Light Degradation Techniques
Several other companies have attempted to use UV light as a method for photochemically dechlorinating PCBs. In all cases it was found that UV alone was not efficient enough to completely dechlorinate PCBs to meet government requirements.
Vertac Chemical Company, Memphis, Tennessee. Vertac has developed an ultraviolet photolysis process for destroying 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) contaminated wastes. They found that this process can also be used to dechlorinate PCBs. Work on the process has stopped, however, pending a review of an EPA order to stop all work and research into the process.
References: (EPA, 1982; Weitzman and Pruce, 1981).
Pure Water Systems Inc.
Pure Water Systems Inc.
4 Edison Place
Fairfield, N.J. 07006
Contact: Tom Creeden
(201) 575-8750
Pure Water Systems (PWS) recently completed laboratory tests which suggest that their ultraviolet purification system may provide an efficient and inexpensive way to degrade PCBs. PWS has patented treatment equipment which maximizes the intensity of the UV source using thin films and automatic cleaning devices on the UV lamps.
By using small volumes of contaminated material and repeated recycling through the system, the process can dehalogenate a 1000 ppm PCB solution to <50 ppm. The waste by-product produced is biphenyl and 380 L of PCB-contaminated liquid can be treated for <$10.
The company plans to mount the system on a mobile platform to preclude transport of PCBs to the main PWS facility.
Reference: (Hazardous Materials Intelligence Report, 1982).
The Oxyphoton Process
Bioferm International
Medford Medical Bldg.,
Stokes Road
Medford, New Jersey 08055.
Contact: Howard E. Worne
(609) 953-1125
In the Oxyphoton® system PCB-contaminated waste liquid containing a special catalyst is spray-atomized and premixed under pressure with an oxygen stream containing 1-2% ozone. It then passes through a high-intensity, 2300 to 2750, UV plasma. The photo-oxidation catalyst causes a series of chemical reactions and breaks the PCB into low molecular weight fragments. As a final step, the effluent is adjusted to pH 6.8-7.2 It is then fed to a normal biological waste treatment facility for final disposal.
The exact stage of development of the Oxyphoton® process is not known, nor is the concentration of PCBs in a waste oil solution which would be treatable.
References: (Worne Biochemicals Inc.; Eco/log Week, 1981).
4.4.3 Oxidation Processes
The oxidation of PCBs to CO2, H2O and HCI is the process involved in conventional and novel incineration. Oxidation at lower temperature does take place to a greater or lesser extent depending on the temperature, solubility of PCB in solvent and the solubility of the oxidant.
Given the chemical stability of PCB it is not surprising that the solvent selection is limited to water and the oxidant to oxygen. There has been some work in Europe on the use of chlorine as an oxidant (producing by-product CCI4) but this concept has apparently not been applied in North America.
As the processes go to lower operating temperatures it becomes more difficult to destroy PCBs, catalysts are required or protracted residence times are needed. One process that is reported to have worked most successfully is described in detail; the Modar Inc., supercritical water process. The others are described in general. The costs are assumed to be similar among these processes. The cost advantage of complete destruction and short residence time offered by Modar may be offset by the need for more robust process equipment.
4.4.3.1 Modar Supercritical Water Process
Head Office: Modar Incorporated
14 Tech Circle
Natick, MA 01760
Contact: Michael Modell
(617) 655-7741
The MODAR Supercritical Water Process (SWP) makes use of air or oxygen as oxidant in an aqueous medium at temperatures above the critical temperature of water, 374°C, and pressures above the critical pressure of water, 218 atmospheres. Under these conditions hydrocarbons and oxygen are almost completely miscible with water and inorganics are generally insoluble.
The MODAR concept, which has only been tested in the laboratory, involves slurrying the waste and pressurizing it for education into the SWP reactor (see Figure 13). The heat generated during oxidation provides motive power to induct waste into the reactor and provide steam to assist the feed and oxidant pressurization. Although not shown on this diagram, a base is added to the system so that anions (such as Cl, P, S) can be reacted to salts and rejected in a salt separator. Residence times of less than 1 minute in the oxidizer are reported with destruction efficiencies of greater than 99.99% for typical hydrocarbons |
