Fig. 2-17 Trend in the amount of dioxins emitted from waste incineration plants

Note: 2004 value and target value of reduction are percentages with respect to 2003. Source: Ministry of the Environment

measures against dioxins, and regulations on exhaust gas and waste water and measures for contaminated soil were stipulated. For example, for dioxins generated in a waste incinerating facility, the emission standard was determined to be $ 0.1 \, ng-TEQ/m^{3}N $ (for incinerators with a 4 t/h or larger capacity). To meet these regulations, various activities have been conducted and the amount of dioxins emitted in 2003 from waste incinerating facilities has been reduced by approximately 98%, compared to 1997 figures (Fig. 2-17).

The development and introduction of excellent technology in harmony with institutional reinforcement has greatly reduced the generation of dioxins. Dioxins are thought to be generated when carbon compounds that remain as unburned material react with chlorine in the course of combustion. For their reduction, it is necessary to keep combustion temperatures at $ 800^{\circ} $ C or higher and make combustion as complete as possible.

The aforesaid new guidelines require new furnaces to maintain a combustion temperature of $ 850^{\circ} $ C or higher for two seconds or longer. According to this requirement, the introduction of full continuous type incineration plants, which can maintain high-temperature combustion for a long period of time, have been promoted, in order to reduce the dioxins generated. Because dioxins are generated at a temperature of about $ 300^{\circ} $ C, under the catalytic action of copper, etc., contained in fly ash, a method is applied that quickly cools exhaust gases from $ 800^{\circ} $ C or higher to $ 200^{\circ} $ C or lower and collects dust in a bag filter. In addition, the technology of spraying activated carbon powder in the inlet of bag filters to adsorb dioxins on the surface of the activated carbon and the technology of letting the exhaust gas flow through a tower filled with activated carbon powder after dust collection to adsorb

## Column: Coexistence of the Reduction of Dioxins and Power Generation from Waste

While it is necessary to reduce the amount of dioxins emitted from waste incinerating facilities, it is also necessary to introduce and expand power generation from waste as a way to cut $ CO_{2} $ emissions. Various measures are being taken, including power utilities' purchasing surplus power of waste power generation and the introduction of the RPS system (the Special Measures Law for the Utilization of New Energy, etc. by Electric Power Suppliers).

To prevent dioxins at waste incinerating facilities, rapid cooling to $ 300^{\circ} $ C is needed, in addition to increasing the combustion temperature and securing the retention time. There was concern that the slow cooling of exhaust gas by the boiler, which is necessary for power generation, may cause the re-synthesis of dioxins, but this problem has been solved by spraying activated carbon in the after-flow, installing a catalytic reaction tower, etc. Today, high-efficiency power generation is possible while reducing dioxins.

Thanks to these measures, the amount of dioxins emitted in 2004 from waste incinerating facilities in Japan was reduced by 98% or more, compared with 1997, while the electricity generated from waste increased 2.2 times. These new technologies are the core 3R technologies for waste management in Japan, where municipal waste is mostly incinerated, and are attracting attention worldwide.