2. Destruction and irreversible transformation methods
The following disposal operations, as provided for in Annexes IV A and IV B of the Basel Convention, should be permitted for the purpose of destruction and irreversible transformation of the POP content in wastes when applied in such a way as to ensure that the remaining wastes and releases do not exhibit the characteristics of POPs:
D9 Physico-chemical treatment;
D10 Incineration on land;
R1 Use as a fuel (other than in direct incineration) or other means to generate energy;
R3 Recycling/reclamation of organic substances which are not used as solvents, but restricted to waste-to-gas conversion;
R4 Recycling/reclamation of metals and metal compounds, but restricted to activities of primary and secondary metallurgy described in (k) below.
POPs that are isolated from the waste during pre-treatment should subsequently be disposed of in accordance with operations D9 and D10.
This subsection describes commercially available operations for the environmentally sound destruction and irreversible transformation of the POP content in wastes.32 It should be noted that the pertinent national legislation applies for these operations.
While the information provided within these guidelines regarding vendors of technologies for destruction and irreversible transformation is believed to be accurate, UNEP disclaims any responsibility for possible inaccuracies or omissions and consequences which may flow from them. Neither UNEP nor any individual involved in the preparation of this report shall be liable for any injury, loss, damage or prejudice of any kind that may be caused by any persons who have acted based on their understanding of the information contained within this publication.
Information on the economics of the following technologies can be found in annex IV.
(a) Alkali metal reduction33
Process description: Alkali metal reduction involves the treatment of wastes with dispersed alkali metal. Alkali metals react with chlorine in halogenated waste to produce salts and non halogenated waste. Typically, the process operates at atmospheric pressure and temperatures between 60°C and 180°C.34 Treatment can take place either in situ (e.g., PCB contaminated transformers) or ex situ in a reaction vessel. There are several variations of this process.35 Although potassium and potassium-sodium alloy have been used, metallic sodium is the most commonly used reducing agent. The remaining information is based on experiences with the metallic sodium variation.
Efficiency: Destruction efficiency (DE) values of greater than 99.999 per cent and destruction removal efficiency (DRE) values of 99.9999 per cent have been reported for aldrin, chlordane and PCBs (Ministry of Environment of Japan, 2004). The sodium reduction process has also been demonstrated to meet regulatory criteria in Australia, Canada, Japan, South Africa, the United States of America and the European Union for PCB transformer oil treatment, i.e., less than 2 ppm in solid and liquid residues.36
Waste types: Sodium reduction has been demonstrated with PCB-contaminated oils containing concentrations up to 10,000 ppm.37 Some vendors have also claimed that this process is capable of treating whole capacitors and transformers.38
Pre-treatment: Ex-situ treatment of PCBs can be performed, however, following solvent extraction of PCBs. Treatment of whole capacitors and transformers could be carried out following size reduction through shearing.39 Pre-treatment should include dewatering to avoid explosive reactions with metallic sodium.
Emissions and residues: Air emissions include nitrogen and hydrogen gas. Emissions of organic compounds are expected to be relatively minor.40It has been noted, however, that PCDDs and PCDFs can be formed from chlorophenols under alkaline conditions at temperatures as low as 150°C (Weber, 2004). Residues produced during the process include sodium chloride, sodium hydroxide, polyphenyls and water.41 In some variations, a solidified polymer is also formed.42
Release control and post-treatment: After the reaction, the by-products can be separated out from the oil through a combination of filtration and centrifugation. The decontaminated oil can be reused, the sodium chloride can either be reused or disposed of in a landfill and the solidified polymer can be disposed of in a landfill.43
Energy requirements: Immediate energy requirements are expected to be relatively low owing to the low operating temperatures associated with the sodium reduction process.
Material requirements: Significant amounts of sodium are required to operate this process.44
Portability: The process is available in transportable and fixed configurations.45
Health and safety: Dispersed metallic sodium can react violently and explosively with water, presenting a major hazard to operators. Metallic sodium can also react with a variety of other substances to produce hydrogen, a flammable gas that is explosive in admixture with air. Great care must be taken in process design and operation absolutely to exclude water (and certain other substances, e.g., alcohols) from the waste and from any other contact with the sodium. In the past, a facility in Delfzijl, the Netherlands, was severely damaged by a fire.
Capacity: Mobile facilities are capable of treating 15,000 litres per day of transformer oil.46
Other practical issues: Sodium reduction used for in-situ treatment of PCB contaminated transformer oils may not destroy all the PCBs contained in the porous internals of the transformer. Some authors have noted that there is a lack of information on the characterization of residues.47
State of commercialization: This process has been used commercially for approximately 20 years.
(a) Dr. Bilger Umweltconsulting GmbH – www.bilgergmbh.de;
(b) Decoman srl, Italy – www.decoman.it;
(c) Envio Germany GmbH & Co. KG – www.envio-group.com;
(d) Kinectrics Inc. – www.kinectrics.com;
(e) Nippon Soda Co. Ltd. – www.nippon-soda.co.jp;
(f) Orion BV, Netherlands – www.orionun2315.nl/en/index.php.
(g) Powertech Labs Inc. – www.powertechlabs.com;
(h) Sanexen Environmental Services Inc. – www.sanexen.com.
(b) Base-catalysed decomposition (BCD)48
Process description: The BCD process involves treatment of wastes in the presence of a reagent mixture consisting of hydrogen-donor oil, alkali metal hydroxide and a proprietary catalyst. When the mixture is heated to above 300°C, the reagent produces highly reactive atomic hydrogen. The atomic hydrogen reacts with the waste to remove constituents that confer the toxicity to compounds.
Efficiency: DEs of 99.99–99.9999 per cent have been reported for DDT, PCBs, PCDDs and PCDFs.49 DEs of greater than 99.999 per cent and DREs of greater than 99.9999 per cent have also been reported for chlordane (Ministry of the Environment of Japan, 2004). It has also been reported that reduction of chlorinated organics to less than 2 mg/kg is achievable.50
Waste types: BCD should be applicable to other POPs in addition to the waste types listed above.51 BCD should be capable of treating wastes with a high POP concentration, with demonstrated applicability to wastes with a PCB content of above 30 per cent.52 It was believed that in practice, the formation of salt within the treated mixture could limit the concentration of halogenated material able to be treated.53 However, the vendor has indicated that the build-up of salt within the reactor simply limits the amount of waste that can be fed to the reactor and that this problem does not appear unsolvable. Applicable waste matrices include soil, sediment, sludge and liquids. The company BCD Group also claims that the process has been shown to destroy PCBs in wood, paper and metal surfaces of transformers.
Pre-treatment: Soils may be treated directly. Different types of soil pre-treatment may be necessary:
(a) Larger particles may need to be removed by sifting and crushed to reduce their size; or
(b) pH and moisture content may need to be adjusted.
Thermal desorption has also been used in conjunction with BCD to remove POPs from soils prior to treatment. In these situations, the soil is pre-mixed with sodium bicarbonate prior to being fed into the thermal desorption unit.54 Water will need to be evaporated from aqueous media, including wet sludge, prior to treatment. Capacitors can be treated following size reduction through shredding.55 If volatile solvents are present, such as occurs with pesticides, they should be removed by distillation prior to treatment.56
Emissions and residues: Air emissions are expected to be relatively minor. The potential to form PCDDs and PCDFs during the BCD process is relatively low. However, it has been noted that PCDDs can be formed from chlorophenols under alkaline conditions at temperatures as low as 150°C (Weber, 2004). Other residues produced during the BCD reaction include sludge containing primarily water, salt, unused hydrogen-donor oil and carbon residue. The vendor claims that the carbon residue is inert and non-toxic. For further details, users are referred to the literature produced by BCD Group, Inc.
Release control and post-treatment: Depending on the type of hydrogen-donor oil used, the slurry residue may be treated in different ways. If No. 6 fuel oil has been used, the sludge may be disposed of as a fuel in a cement kiln. If more refined oils are used, these may be removed from the sludge by gravity or centrifuge separation. The oils can then be reused and the remaining sludge can be further treated for use as a neutralizing agent or disposed of in a landfill.57 In addition, BCD plants are equipped with activated carbon traps to minimize releases of volatile organics in gaseous emissions.
Energy requirements: Energy requirements are expected to be relatively low owing to the low operating temperatures associated with the BCD process.
(a) Hydrogen-donor oil, such as No. 6 fuel oil or Sun Par oils No. LW-104, LW-106 and LW 110;
(b) Alkali or alkaline earth metal carbonate, bicarbonate or hydroxide, such as sodium bicarbonate. The amount of alkali required is dependent on the concentration of the halogenated contaminant contained in the medium.58 Amounts range from 1 per cent to about 20 per cent by weight of the contaminated medium; and
(c) Proprietary catalyst amounting to 1 per cent by volume of the hydrogen donor oil.
The equipment associated with this process is thought to be readily available.59
Portability: Modular, transportable and fixed plants have been built.
Health and safety: In general, the health and safety risks associated with operation of this technology are thought to be low,60 although a BCD plant in Melbourne, Australia, was rendered inoperable following a fire in 1995. The fire is thought to have resulted from the operation of a storage vessel without a nitrogen blanket.61 Some associated pre-treatments such as alkaline pre-treatment of capacitors and solvent extraction have significant fire and explosion risks, although they can be minimized through the application of appropriate precautions.62
Capacity: BCD can process as much as 2,600 gallons per batch, with a capability of treating two–four batches per day.63
Other practical issues: Since the BCD process involves stripping chlorine from the waste compound, the treatment process may result in an increased concentration of lower-chlorinated species. This can be of potential concern in the treatment of PCDDs and PCDFs, where the lower chlorinated congeners are more toxic than the higher-chlorinated congeners. It is therefore important that the process be appropriately monitored to ensure that the reaction continues to completion. In the past, it has been reported that the BCD process was unable to treat high-concentration wastes because of salt build-up.64 More recently, however, it has been reported that this problem has been overcome.65
State of commercialization: BCD has been used at two commercial operations within Australia, with one still operating. Another commercial system has been operating in Mexico for the past two years. In addition, BCD systems have been used for short-term projects in Australia, Spain and the United States of America. A BCD unit for the treatment of both soil and pesticide wastes contaminated with PCDDs and PCDFs is now under construction within the Czech Republic.
Vendors: The patent for this technology is held by BCD Group, Inc., USA (www.bcdinternational.com). BCD Group, Inc. sells licences to operate the technology. Currently, licences are held by companies based in Australia, the Czech Republic, Japan, Mexico and the United States of America.
(c) Catalytic hydrodechlorination (CHD)
Process description: CHD involves the treatment of wastes with hydrogen gas and palladium on carbon (Pd/C) catalyst dispersed in paraffin oil. Hydrogen reacts with chlorine in halogenated waste to produce hydrogen chloride (HCl) and non-halogenated waste. In the case of PCBs, biphenyl is the main product. The process operates at atmospheric pressure and temperatures between 180°C and 260°C (Sakai, Peter and Oono, 2001; Noma, Sakai and Oono, 2002; and Noma, Sakai and Oono, 2003a and 2003b).
Efficiency: DEs of 99.98–99.9999 per cent have been reported for PCBs. It has also been reported that a reduction of the PCB content to less than 0.5 mg/kg is achievable.
Waste types: CHD has been demonstrated with PCBs removed from used capacitors. PCDDs and PCDFs contained in PCBs as impurities have also been dechlorinated. A vendor has also claimed that chlorinated wastes in liquid state or dissolved in solvents can be treated by CHD.
Pre-treatment: PCBs and PCDDs/PCDFs must be extracted using solvents or isolated by vaporization. Substances with low boiling points such as water or alcohols should be removed by distillation prior to treatment.
Emission and residues: No emissions would occur during the dechlorination reaction because it takes place in the closed hydrogen circulation system. HCl is not discharged from the reaction because it is collected with water as hydrochloric acid within the circulation system. Biphenyl isolated after the reaction by distillation does not contain any toxic materials.
Release control and post-treatment: Biphenyl, the main product, is separated out from the reaction solvent by distillation after the reaction, and the catalyst and reaction solvent are reused for the next reaction.
Energy requirements: Energy requirements are expected to be relatively low owing to the low operating temperatures associated with the CHD process.
Material requirements: The CHD process requires the same number of atoms of hydrogen as those of chlorine in the PCBs, and also 0.5 per cent by weight of catalyst.
Portability: CHD is available in fixed and transportable configurations depending on the volume of PCBs to be treated.
Health and safety: The use of hydrogen gas requires adequate controls and safeguards to ensure that explosive air-hydrogen mixtures are not formed.
Capacity: In Japan, a plant which is capable of treating 2 Mg PCB per day using the CHD process is currently being designed and will be constructed in two years.
Other practical issues: There are many reports about PCB dechlorination by using CHD. Generally, Pd/C catalyst shows the largest degradation rate compared to the other supported metal catalysts. Reaction temperature can be increased to 260°C when paraffin oil is used as reaction solvent.
State of commercialization: A company in Japan started to treat capacitors containing or contaminated with PCBs using a CHD plant in 2004. A commercial-scale CHD plant will be in operation in two years in Japan.
Vendor(s): The patent for this technology is held by Kansai Electric Power Co and Kanden Engineering Co. (www.kanden-eng.co.jp).
Additional information: For further information, see the Technical Guideline for Treatment of PCBs in Japan (Japan Industrial Waste Management Foundation, 1999).