dioxins, have been introduced. Additionally, for soot and dust (fly ash and soot) that are generated in the course of incineration, dioxins criteria (3 ng-TEQ/g or less) have been established. To achieve this, technology has been introduced that heats fly ash from 350 to 450°C in oxygen deficient conditions to pyrolytically decompose dioxins.

## (3) PCB

PCB (polychlorinated biphenyl) is an industrially synthesized compound that is less susceptible to thermal decomposition and has other excellent properties, such as high electric insulation and chemical stability. So, it has been used as insulating oil in electric equipment, such as high-voltage transformers, high-voltage capacitors and ballast and as a heating medium in heat exchangers, etc. (Fig. 2-18). However, the Kanemi Oil Poisoning Incident of 1968 brought its toxicity to light and led to a ban on the production, import and use of PCBs in 1974. After that, although the treatment standard by high-temperature incineration was established in 1976, there was no progress in its treatment, except in some areas, due to objections by residents. So, waste PCBs continued to be stored in enterprises for more than 30 years. There was anxiety that waste PCBs, as a negative legacy, could go missing or leak out during long-term storage and cause environmental pollution.

On the other hand, activities against organic pollutants were progressing internationally and the Stockholm Convention on Persistent Organic Pollutants (POPs Convention) took effect in May 2004 (Japan ratified the Convention in August 2002). Concerning PCBs, the Convention requires a ban on their use by 2025 and appropriate treatment of these substances by 2028.

In these circumstances, the Law Concerning Special Measures against PCB Waste (PCB Special Measures Law) was enacted in 2001, requiring enterprises to dispose of their PCB waste by 2016. Therefore, a nationwide PCB waste management system based on regional disposal facilities is now being established, utilizing the Japan Environmental Safety Corporation. As technologies for safely and surely disposing of PCBs, five methods (dechlorination decomposition, hydrothermal oxidation decomposition,

Fig. 2-18 Chemical structure of polychlorinated biphenyl (PCB)

Note: Chlorine atom is bound to the numbered section.

reductive thermochemical decomposition, photodecomposition and plasma decomposition) are stipulated, in addition to high-temperature incineration (Table 2-3).

As a pioneer project in Japan, in the Kitakyushu PCB waste management facility (first phase) of the Japan Environmental Safety Corporation, which started operation in December 2004, the decomposition of PCBs by the dechlorination decomposition method and, as its pretreatment, solvent cleaning and vacuum heating separation for removing PCBs from transformers, etc., have been enacted for electric equipment, such as high-voltage transformers and

Table 2-3 PCB treatment methods

Name	Method	Features
High-temperature incineration	PCB is made into fine droplets to be sprayed in a furnace and incinerated.	Cost-effective method but combustion gas is generated by incineration.
Dechlorination decomposition	Sufficiently mixed with chemicals, etc. to be decomposed by dechlorination reaction.	Main product is dechlorinated treated oil. This method also includes catalytic decomposition.
Hydrothermal oxidation decomposition	Decomposed in high-temperature high-pressure water	Organic matter containing PCB is decomposed into inorganic substances, i.e. carbon dioxide, water and salts. The main product is treated water.
Reductive thermochemical decomposition	Decomposed in a reducing atmosphere	The main product is reducing gas of methane, carbon monoxide, etc.
Photo-decomposition	Decomposed by photochemical reaction	PCB is low-chlorinated by photodecomposition, and the mixture after reaction is treated by dechlorination decomposition or biological decomposition. The main product is treated oil or treated water.
Plasma decomposition	Decomposed by plasma at high temperature	The main products are carbon monoxide, carbon dioxide, hydrogen chloride, hydrogen, etc.

Source: Ministry of the Environment